WO2021156026A1 - Method for calibrating the extrinsic characteristics of a lidar - Google Patents

Method for calibrating the extrinsic characteristics of a lidar Download PDF

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Publication number
WO2021156026A1
WO2021156026A1 PCT/EP2021/050518 EP2021050518W WO2021156026A1 WO 2021156026 A1 WO2021156026 A1 WO 2021156026A1 EP 2021050518 W EP2021050518 W EP 2021050518W WO 2021156026 A1 WO2021156026 A1 WO 2021156026A1
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WO
WIPO (PCT)
Prior art keywords
lidar
vehicle
yaw
angle
pitch
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PCT/EP2021/050518
Other languages
French (fr)
Inventor
Gatien FERRET
Lucien Garcia
Boris Lugez
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Continental Automotive Gmbh
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Publication date
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Publication of WO2021156026A1 publication Critical patent/WO2021156026A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/497—Means for monitoring or calibrating
    • G01S7/4972—Alignment of sensor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/93—Lidar systems specially adapted for specific applications for anti-collision purposes
    • G01S17/931—Lidar systems specially adapted for specific applications for anti-collision purposes of land vehicles

Definitions

  • the present invention relates to a method for calibrating the extrinsic characteristics of a laser telemetry mapping system on board a motor vehicle. More particularly, the invention relates to a method for calibrating the extrinsic characteristics of a Lidar (acronym for "Light Detection and Ranging" in English) intended to be mounted on a motor vehicle.
  • a Lidar ascronym for "Light Detection and Ranging" in English
  • ADAS Advanced Driver Assistance System
  • a Lidar for example mounted on the vehicle, which makes it possible to generate a dense point cloud representing the environment of the vehicle.
  • a processing unit in order to assist the driver, for example by detecting an obstacle.
  • the information given by the images acquired by the lidar must therefore be sufficiently reliable and relevant to allow the system to assist the driver of the vehicle.
  • the lidar calibration operation To use the information contained in these three-dimensional images, it is necessary to first carry out the lidar calibration operation to find a relationship between the spatial coordinates of a point in space with the associated point in the image taken by the Lidar as well as the spatial relationship between the Lidar and the vehicle.
  • This spatial relationship makes it possible to go from a point of the reference frame associated with the vehicle to a point of the image which depends in a known manner on intrinsic parameters specific to the lidar and on extrinsic parameters.
  • the intrinsic parameters consist, for example, of the focal length, the enlargement factors of the Lidar image, the factors of the distortion model and the position of the central point.
  • the extrinsic parameters are related to the position and orientation of the lidar relative to the vehicle. These parameters include a rotation matrix representative of the orientation of the lidar and the translation vector making it possible to go from the reference mark associated with the vehicle to the reference mark associated with the lidar.
  • the extrinsic parameters therefore include the three translations and the three roll, pitch and yaw angles (respectively "roll”, “pitch” and “yaw” in English) according to a formalism known to those skilled in the art.
  • the Lidar is a long-range Lidar whose field of view is relatively small, typically of the order of +/- 9 ° in the horizontal direction and +/- 4.5 ° in the vertical direction and the viewing distance which can go up to 200 m, the positioning errors of the Lidar are particularly critical and can have a direct impact on the quality of detection.
  • the calibration of the extrinsic parameters is carried out a first time in the factory at the end of the vehicle manufacturing process and is then generally repeated subsequently, for example at a garage or a dealer during a maintenance session, in order to compensate only the values of the extrinsic parameters of the lidar.
  • the calibration method consists in positioning the vehicle in front of a calibration support also called a "test pattern" and in acquiring images of the landmarks of this test target while maintaining the vehicle. static during image acquisition. The images are then processed to determine the values of the extrinsic parameters.
  • Such a calibration support comprises a mark or a plurality of calibration marks.
  • a first step it is necessary to align as precisely as possible the vehicle facing the calibration support by means of a laser system so that their respective three-dimensional reference frames are parallel so as to cancel the rotation values while fixing the translation values in three dimensions between the vehicle and the calibration support. This alignment should be done so that the alignment error is less than the calibration tolerance.
  • the lidar acquires at least one image of the calibration medium as a whole in order to determine the values of rotation and translation between the lidar and the calibration marks of the calibration medium.
  • Such a method therefore requires precise alignment of the vehicle facing the calibration support or a measurement of the position of the calibration support relative to the vehicle, which requires time and expensive implementation means such as specific alignment platform, lasers.
  • Using a specific alignment platform requires moving the vehicle off the production line, which leads to increased implementation costs.
  • the proposed solution makes it possible to overcome costly technical constraints such as the use of a laser system to produce a precise alignment between the vehicle and the calibration bracket or a measurement of the position of the calibration bracket relative to the vehicle.
  • the invention relates to a method for calibrating a Lidar, from a calibration test chart, said Lidar being mounted on an area of the motor vehicle, with a view to acquiring three-dimensional images of the staff positioned on flat ground, said calibration comprising the determination of the values of the extrinsic parameters of the three components of rotation comprising the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the angle yaw (yaw_L / V) between the mark linked to the lidar (RL) and the mark linked to the vehicle (Rv), the calibration process comprising the following steps:
  • step (E1) positioning the target on the flat ground, said target comprising at least three non-collinear reference points, said reference points being arranged in a reference frame associated with the target (RM);
  • step (E2) moving the vehicle along a substantially rectilinear path in the direction of the test pattern and simultaneously capturing by means of said Lidar a series of images of the landmarks;
  • step (E3) determine a value of the three translation components and a value of the roll angles (roll_L / M), pitch (pitch_L / M) and yaw (Yaw_L / M) between the reference associated with the Lidar (RL) and the mark associated with the test pattern (RM) from an image or a set of images extracted from said series of images;
  • step (E4) construct the trajectory of the vehicle in the frame of reference associated with the test pattern from a set of values of the three translation components determined in step (E3) between the frame of reference associated with the lidar (RL) and the mark associated with the staff (RM);
  • yaw_V / M a value of the yaw angle (yaw_V / M) between the mark associated with the vehicle (Rv) and the mark associated with the test pattern (RM) from the trajectory of the vehicle in the mark associated with the staff (RM);
  • a value of the yaw angle (yaw_L / V) between the mark associated with the lidar (RL) and the mark associated with the vehicle (Rv) from the difference between the value of l 'yaw angle (yaw_V / M) determined in step (E5) and the value of the yaw angle (yaw_L / M) determined in step (E3) from a image or a set of images extracted from said series of images;
  • step (E7) deduce the values of the three rotation components of the roll angle (roll_L / V), of the pitch angle (pitch_L / V) and of the yaw angle (yaw_L / V ) between the marker associated with the lidar (RL) and the marker associated with the vehicle (Rv).
  • the vehicle is positioned at an initial distance from the calibration test pattern greater than or equal to a predetermined distance threshold Dmin.
  • the longitudinal distance Lx between two reference points and the lateral distance Ly between two reference points is respectively equal to or greater than a distance threshold predefined by the resolution of said lidar.
  • the Lidar is mounted at the front, rear or side of the vehicle, and the staff is positioned on the level ground so that it is in the field of view of the Lidar.
  • a device for calibrating a Lidar such as a Lidar from a calibration test chart, said Lidar being mounted on an area of the motor vehicle, with a view to to acquire three-dimensional images of the staff positioned on a flat ground
  • said calibration comprising the determination of the values of the extrinsic parameters of the three components of rotation including the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the yaw angle (yaw_L / V) between the reference linked to the lidar (RL) and the reference linked to the vehicle (Rv)
  • said device comprising:
  • test target comprising at least three non-collinear reference points
  • Lidar capable of being mounted on a vehicle and configured to generate a series of three-dimensional images of the test pattern during a rectilinear movement of said vehicle on the portion of flat ground in the direction of the test target;
  • processing unit configured for:
  • FIG. 1 schematically illustrates a top view of the vehicle and of the device for calibrating the extrinsic parameters according to one embodiment of the invention
  • FIG. 2 schematically illustrates the mark (Rv) linked to a vehicle, the mark (RL) linked to the imaging device mounted on the windshield of the vehicle and the mark (RM) linked to the calibration test pattern;
  • FIG. 3 schematically illustrates a top view of the position of the vehicle at two different times during its movement, showing the presence of a yaw angle yaw_V / M between the mark (Rv) linked to the vehicle and the mark (RM ) linked to the calibration target;
  • FIG. 4 schematically illustrates the reconstructed trajectory of the vehicle and the yaw angle yaw_V / M between the vehicle frame and the calibration target mark deduced from the trajectory of the vehicle in the target frame (RM);
  • FIG. 5 Figure 5 schematically illustrates one embodiment of the invention.
  • the calibration device 10 comprises a Lidar 2 positioned here in Figure 1 at the front of the vehicle, at the bumper and a processing unit 4 configured to process three-dimensional images recorded by the Lidar and to determine the extrinsic Lidar calibration parameters.
  • the lidar can also be positioned at the rear of the vehicle.
  • the lidar can also be mounted on the side of the vehicle.
  • the calibration device 10 is intended for use in a driver assistance system mounted in the vehicle in order to assist the driver in his driving.
  • the device 10 of the present disclosure makes it possible to determine the extrinsic Lidar calibration parameters, namely the three components of rotation, the angle of roll, pitch and yaw of the Lidar with respect to the vehicle.
  • the extrinsic parameters determined by the calibration device 10 can also be used to adjust the positioning of the lidar relative to the vehicle at the factory at the end of the vehicle manufacturing process so that it can fulfill the criteria of an operation optimal.
  • optimal operation corresponds to detection of an object located at a distance of 200 m and in a field of view of ⁇ 10 °.
  • the Lidar is mounted in the bumper of the vehicle so as to observe the road on which the vehicle is traveling as well as the environment of the vehicle located in the field of view of the Lidar.
  • the processing unit 4 and the lidar 2 are implemented by the same physical entity.
  • they can each be made up of a separate physical entity, interconnected by a wired link or a communication network.
  • the calibration device comprises a sight 3 which is positioned on the flat ground so as to be in the field of view of the Lidar.
  • the Lidar being at the front of the vehicle
  • the sight is positioned at the front of the vehicle on the ground, and arranged so that the sight extends in a horizontal plane. (XM, YM) forming an orthonormal coordinate system.
  • a frame of reference linked to the test pattern here called a target mark Rm is defined by three axes XM, YM and ZM.
  • the axes of the sight are practically aligned to a few degrees of close relative to the axes of the reference mark associated with the vehicle defined below.
  • the ZM axis of the staff and the Zv axis of the vehicle are parallel.
  • the target comprises a network of at least three benchmarks 5 arranged at regular intervals aligned along the axis (XM) and along the axis (YM), in the frame associated with the target.
  • the longitudinal distance Lx between two reference points along the axis (XM) and the lateral distance Ly between two reference points along the axis (Y) are respectively equal to or greater than a threshold distance predefined according to the resolution of the imaging device.
  • the lateral distance Ly between two points is 0.5m and the longitudinal distance Lx between two points is 1.5m.
  • the calibration target is positioned at an initial distance D relative to the front of the vehicle which is equal to or greater than a predetermined distance threshold Dmin.
  • This distance threshold is determined so that the point of view closest to the vehicle is in the field of view of the Lidar.
  • the value of this distance threshold varies between 4.2 m and 12.5 m when the lidar is rotated vertically by an angle of 4.5 ° and positioned at a height of 0.5 m by relative to the ground.
  • the test chart 3 remains fixed for the duration of the calibration of the lidar 2.
  • a mark is also linked to the vehicle Rv, here called a vehicle mark which is defined by three axes Xv, Yv and Zv.
  • the Xv axis corresponds to the longitudinal horizontal direction of the vehicle facing the front of the vehicle
  • the Yv axis corresponds to the transverse horizontal direction of the vehicle
  • a third Zv axis corresponds to the vertical direction of the vehicle.
  • the axes Xv, Yv and Zv originate from the ground by convention.
  • An RL frame specific to the Lidar is defined by three axes XL, YL and ZL.
  • the XL axis is the optical axis of the Lidar and is practically parallel to the Xv axis.
  • the YL axis is practically parallel to the Yv axis and the ZL axis is practically parallel to the Zv axis.
  • this alignment condition is not necessary, it suffices to position the lidar with respect to the vehicle so that the target is in the field of view of the lidar.
  • the method according to the present disclosure aims to determine the three angles of rotation making it possible to go from the Lidar RL marker to the Rv vehicle marker.
  • the angles of rotation therefore include the roll angle, the pitch angle and the yaw angle which correspond respectively to the angle of rotation around the X axis, the angle of rotation around the Y axis and the angle of rotation about the Z axis.
  • the lidar is mounted on a support comprising a motorized axis for vertically pivoting along the YL axis the direction of acquisition of images of the lidar.
  • the Lidar is configured to generate a series of images of the calibration pattern, in particular during a rectilinear movement of the vehicle on a portion of flat ground in the direction of the pattern.
  • a series of images therefore includes a succession of images acquired by the Lidar while causing the vehicle to move in a rectilinear movement.
  • the series of images comprises for example a first image taken at time t by the Lidar after a first movement of the vehicle, a second image taken at time t + 1 by the Lidar after a second movement of the vehicle .
  • the processing unit 4 is configured to receive a series of images of the test pattern 3 of the vehicle acquired by the Lidar and to determine the extrinsic parameters of the Lidar calibration.
  • the processing unit is configured to determine from at least two images extracted from the series of images the values of the extrinsic parameters of the three components of rotation, namely the roll angle (roll_L / V), the pitch angle (pitch_L / V) and yaw angle (yaw_L / V) to go from the Lidar reference (RL) to the reference linked to the vehicle (Rv).
  • the processing unit is configured to determine the values of the three translation components and the values of the roll angles (roll_L / M), pitch (pitch_L / M) and yaw (yaw_L / M) between the reference mark associated with the Lidar (RL) and the mark associated with the test pattern (RM) for each of the images extracted from the series of images of the calibration test pattern. These values are determined using a minimization method.
  • the method of determining the values comprises the following steps:
  • the parameters are determined from a Levenberg-type gradient descent algorithm.
  • the roll angle (roll_L / M) between the Lidar mark and the target mark and the roll angle ( roll_L / V) between the lidar marker and the vehicle marker have the same value.
  • the pitch angle (pitch_L / M) between the Lidar coordinate system and the target mark and the pitch angle (pitch_L / V) between the Lidar coordinate system and the vehicle coordinate system have the same value. It is noted here that the rectilinear movement of the vehicle in the direction of the target does not necessarily mean that the movement of the vehicle is parallel to an alignment of reference points 5 of the target.
  • the processing unit 4 is configured to build the trajectory of the vehicle in the frame associated with the test pattern (RM) from a set of values of the three translation components determined to go from the frame associated with the lidar (RL ) to the mark associated with the staff (RM). 3D linear regression was used.
  • FIG. 4 illustrates an example of a straight line representative of the trajectory of the vehicle in the target mark.
  • the transverse coordinates Y are represented on the abscissa and the longitudinal coordinates X are represented on the ordinate.
  • the different points represent the positions of the vehicle at different times. It is thus possible to deduce the yaw angle (yaw_V / M) between the vehicle frame and the target frame. This deduction is based on the fact that when the vehicle has a straight rectilinear motion, the direction of motion is collinear with the Xv axis. Thus, the yaw angle between the XM axis and the vehicle path corresponds to the yaw angle between the XM axis and the Xv axis.
  • This angle is also shown in Figure 3 which illustrates the position of the vehicle in the target mark at two times during its movement along a rectilinear path. This is the angle between the line (di) parallel to the longitudinal axis (XM) of the target mark and the line (d2) representative of the direction of movement of the vehicle which is parallel to the Xv axis.
  • the processing unit 4 can then determine a value of the yaw angle (yaw_L / V) between the mark associated with the lidar (RL) and the mark associated with the vehicle (Rv) from the difference between the value of the yaw angle (yaw_V / M) between the vehicle reference and the target mark and the value of the yaw angle (yaw_L / M) between the lidar reference and the target mark.
  • the value of the yaw angle (yaw_L / M) between the Lidar frame and the target frame is determined from an image or a set of images extracted from the series of images acquired by the Lidar. According to an advantageous embodiment, it is possible to obtain an average value of the yaw angle (yaw_L / M) between the Lidar frame and the target frame from a set of images extracted from the series of images to improve the accuracy of the value.
  • the processing unit makes it possible to deduce the values of the three components of rotation of the roll angle (rollJ V), of the pitch angle (pitch_L / V) and of the yaw angle (yaw_L / V) between the Lidar marker (RL) and the marker associated with the vehicle (Rv).
  • the calibration target is positioned in front of the vehicle.
  • the calibration target is positioned at the end of the vehicle's production line on level ground.
  • the positioning of the sight is carried out so that the vehicle mark is substantially aligned with respect to the sight mark as illustrated in FIG. 1 and that the sight is in the field of view of the Lidar.
  • a step E2 the vehicle 1 moves along a rectilinear path over a portion of flat ground in the direction of the sight along the axis (XM) and the Lidar simultaneously captures a series of images of the landmarks of the sights.
  • a step E3 one determines according to a known minimization method from an image the values of the three components of translation and the values of rotation of the angles of roll (roll_L / M), of pitch (pitch_L / M ) and yaw (yaw_L / M) between the reference associated with the lidar (RL) and the reference associated with the test pattern (RM).
  • roll_L / M the values of the angles of rotation determined between the lidar frame and the target frame are constant. Due to the flatness of the ground, the values of the pitch and roll rotation angles between the lidar frame and the target frame are also those of the pitch and roll rotation angles between the lidar frame and the vehicle frame.
  • step E3 is performed only for an image extracted from said series of images.
  • this image can be the image acquired by the vehicle in its initial position located at a distance D greater than or equal to Dmin relative to the vehicle.
  • step E3 is repeated and carried out for each of the images extracted from said series of images. We then obtain a set of values of the three translations and the three rotations. From this set of values, it is therefore possible to calculate the average of the values of the three angles of rotation.
  • a step E4 the trajectory of the vehicle is constructed in the frame associated with the test pattern from a set of values of the three translation components determined between the Lidar frame (RL) and the frame associated with the pattern ( RM) determined in step E3 from at least two images.
  • This trajectory is represented through a set of points representative of the positions of the vehicle during its movement in the target mark as illustrated in Figure 4.
  • a value of the yaw angle (yaw_V / M) is determined between the mark associated with the vehicle (Rv) and the mark associated with the test pattern (RM) from the trajectory of the vehicle constructed in step E4.
  • a value of the yaw angle (yaw_LA /) is determined between the mark associated with the lidar (RL) and the mark associated with the vehicle (Rv) from the difference between the value of the yaw angle (yaw_V / M) determined in step (E5) and a value of the yaw angle (yaw_L / M) determined in step (E3) for each of the images extracted from said series of images;
  • the values of the three rotation components are deduced from the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the yaw angle ( yaw_L / V) between the reference associated with the lidar (RL) and the reference associated with the vehicle (Rv).
  • the values of the three components of rotation reflect a misalignment between the lidar frame and the vehicle frame. Knowing these values makes it possible to adjust the positioning of the lidar in relation to the vehicle.
  • the calibration process can advantageously be carried out in the factory, at the end of the production line by causing the vehicle to move in the direction of the target only over a few meters.
  • the invention makes it possible to determine the extrinsic parameters of a lidar quickly by means of a test chart, easily and reliably.
  • the implementation of the calibration process does not require the use of a laser system to achieve precise alignment between the vehicle and the staff or to measure the position of the staff relative to the vehicle.
  • the invention may find application in particular in a system for assisting the driving of a motor vehicle. It is also advantageously applicable to the calibration of a camera or a lidar.

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  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
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Abstract

The present invention relates to a method for calibrating a lidar (2), in particular a long range lidar, the purpose of which is to determine the extrinsic parameter values of the three rotational components, the roll angle (roll_L/V), the pitch angle (pitch_L/V) and the yaw angle (yaw_L/V) between the reference frame linked to the lidar (RL) and the reference frame linked to the vehicle (RV), from a series of three-dimensional images of a calibration test pattern (3) positioned on flat ground, the images being acquired by the lidar, which is fitted on a region of the motor vehicle (1), while the vehicle moves towards the test pattern.

Description

Description Description
Titre : Procédé de calibration des caractéristiques extrinsèques d’un Lidar Title: Method for calibrating the extrinsic characteristics of a lidar
Domaine technique Technical area
[0001] La présente invention concerne un procédé de calibration des caractéristiques extrinsèques d’un système de cartographie par télémétrie laser embarqué dans un véhicule automobile. Plus particulièrement, l’invention concerne un procédé de calibration des caractéristiques extrinsèques d’un Lidar (acronyme pour « Light Détection and Ranging » en langue anglaise) destiné à être monté sur un véhicule automobile. The present invention relates to a method for calibrating the extrinsic characteristics of a laser telemetry mapping system on board a motor vehicle. More particularly, the invention relates to a method for calibrating the extrinsic characteristics of a Lidar (acronym for "Light Detection and Ranging" in English) intended to be mounted on a motor vehicle.
Technique antérieure Prior art
[0002] L’état de la technique comprend les documents U S2019/094347 et US2014/347206. [0002] The state of the art includes documents U S2019 / 094347 and US2014 / 347206.
[0003] De nos jours, il est connu d’équiper un véhicule automobile d’un système d’assistance à la conduite appelée communément ADAS (« Advanced Driver Assistance System » en anglais). Un tel System comprend de manière connue un Lidar, par exemple monté sur le véhicule, qui permet de générer un nuage de points dense représentant l’environnement du véhicule. Ces images tridimensionnelles sont ensuite exploitées par une unité de traitement dans le but d’assister le conducteur, par exemple en détectant un obstacle. Les informations données par les images acquises par le lidar doivent donc être suffisamment fiables et pertinentes pour permettre au système d’assister le conducteur du véhicule. [0003] Nowadays, it is known to equip a motor vehicle with a driving assistance system commonly called ADAS ("Advanced Driver Assistance System"). Such a System comprises, in a known manner, a Lidar, for example mounted on the vehicle, which makes it possible to generate a dense point cloud representing the environment of the vehicle. These three-dimensional images are then used by a processing unit in order to assist the driver, for example by detecting an obstacle. The information given by the images acquired by the lidar must therefore be sufficiently reliable and relevant to allow the system to assist the driver of the vehicle.
[0004] Pour exploiter les informations contenues dans ces images tridimensionnelles, il est nécessaire de procéder au préalable à l’opération de calibration du lidar pour trouver une relation entre les coordonnées spatiales d’un point de l’espace avec le point associé dans l’image prise par le Lidar ainsi que la relation spatiale entre le Lidar et le véhicule. Cette relation spatiale permettant de passer d’un point du repère associé au véhicule à un point de l’image qui dépend de manière connue de paramètres intrinsèques propres au Lidar et de paramètres extrinsèques. [0005] Les paramètres intrinsèques sont constitués, par exemple par la distance focale, les facteurs d’agrandissement de l’image du Lidar, les facteurs du modèle de distorsion et la position du point central. To use the information contained in these three-dimensional images, it is necessary to first carry out the lidar calibration operation to find a relationship between the spatial coordinates of a point in space with the associated point in the image taken by the Lidar as well as the spatial relationship between the Lidar and the vehicle. This spatial relationship makes it possible to go from a point of the reference frame associated with the vehicle to a point of the image which depends in a known manner on intrinsic parameters specific to the lidar and on extrinsic parameters. [0005] The intrinsic parameters consist, for example, of the focal length, the enlargement factors of the Lidar image, the factors of the distortion model and the position of the central point.
[0006] Les paramètres extrinsèques sont liés à la position et à l’orientation du Lidar par rapport au véhicule. Ces paramètres comprennent une matrice de rotation représentative de l’orientation du Lidar et le vecteur de translation permettant de passer du repère associé au véhicule au repère associé au Lidar. Les paramètres extrinsèques comprennent donc les trois translations et les trois angles de roulis, de tangage et de lacet (respectivement « roll », « pitch » et « yaw » en anglais) selon un formalisme connu de l’homme du métier. [0006] The extrinsic parameters are related to the position and orientation of the lidar relative to the vehicle. These parameters include a rotation matrix representative of the orientation of the lidar and the translation vector making it possible to go from the reference mark associated with the vehicle to the reference mark associated with the lidar. The extrinsic parameters therefore include the three translations and the three roll, pitch and yaw angles (respectively "roll", "pitch" and "yaw" in English) according to a formalism known to those skilled in the art.
[0007] Il est donc nécessaire de déterminer préalablement les valeurs des paramètres intrinsèques et/ou les valeurs des paramètres extrinsèques qui permettent de compenser à la fois les erreurs de fabrication propres au Lidar et/ou les erreurs de positionnements du Lidar par rapport au véhicule. [0007] It is therefore necessary to determine beforehand the values of the intrinsic parameters and / or the values of the extrinsic parameters which make it possible to compensate both the manufacturing errors specific to the Lidar and / or the positioning errors of the Lidar relative to the vehicle .
[0008] En outre, dans le cas où le Lidar est un Lidar longue portée dont le champ de vue est relativement restreint, typiquement de l’ordre de +/- 9° dans la direction horizontale et +/- 4,5° dans la direction verticale et la distance de vue qui peut aller jusqu’à 200 m, les erreurs de positionnement du Lidar sont particulièrement critiques et peuvent avoir un impact direct sur la qualité de détection. [0008] In addition, in the case where the Lidar is a long-range Lidar whose field of view is relatively small, typically of the order of +/- 9 ° in the horizontal direction and +/- 4.5 ° in the vertical direction and the viewing distance which can go up to 200 m, the positioning errors of the Lidar are particularly critical and can have a direct impact on the quality of detection.
[0009] Ainsi, il est essentiel de pouvoir déterminer les valeurs numériques des paramètres extrinsèques afin de pouvoir corriger éventuellement la position du Lidar lors de son montage en usine à la fin du processus de fabrication du véhicule. [0009] Thus, it is essential to be able to determine the digital values of the extrinsic parameters in order to be able to possibly correct the position of the lidar during its assembly in the factory at the end of the vehicle manufacturing process.
[0010] La calibration des paramètres extrinsèques est réalisée une première fois en usine à la fin du processus de fabrication du véhicule puis est ensuite généralement répétée postérieurement, par exemple chez un garagiste ou un concessionnaire lors d’une séance de maintenance, afin de compenser uniquement les valeurs des paramètres extrinsèques du Lidar. The calibration of the extrinsic parameters is carried out a first time in the factory at the end of the vehicle manufacturing process and is then generally repeated subsequently, for example at a garage or a dealer during a maintenance session, in order to compensate only the values of the extrinsic parameters of the lidar.
[0011] Selon une méthode connue, le procédé de calibration consiste à positionner le véhicule devant un support de calibration encore appelé « mire » et à acquérir des images des points de repères de cette mire tout en maintenant le véhicule statique pendant l’acquisition des images. Les images sont ensuite traitées afin de déterminer les valeurs des paramètres extrinsèques. [0011] According to a known method, the calibration method consists in positioning the vehicle in front of a calibration support also called a "test pattern" and in acquiring images of the landmarks of this test target while maintaining the vehicle. static during image acquisition. The images are then processed to determine the values of the extrinsic parameters.
[0012] Un tel support de calibration comporte un repère ou une pluralité de repères de calibration. Dans une première étape, il est nécessaire d’aligner de manière la plus précise possible le véhicule face au support de calibration au moyen d’un système laser afin que leurs référentiels tridimensionnels respectifs soient parallèles de manière à annuler les valeurs de rotations tout en fixant les valeurs de translation dans les trois dimensions entre le véhicule et le support de calibration. Cet alignement doit être réalisé de sorte que l’erreur d’alignement soit inférieure à la tolérance de calibration. Ensuite, le Lidar acquiert au moins une image du support de calibration dans son ensemble afin de déterminer les valeurs de rotation et de translation entre le Lidar et les repères de calibration du support de calibration. Enfin, connaissant les valeurs de rotation et de translation entre le véhicule et le support de calibration et d’autre part les valeurs de rotation et de translation entre le Lidar et les repères du support de calibration, on en déduit les valeurs des paramètres extrinsèques de calibration du Lidar qui sont ensuite stockées et utilisées par le système d’assistance à la conduite du véhicule afin de compenser en permanence le Lidar lors de son utilisation. [0012] Such a calibration support comprises a mark or a plurality of calibration marks. In a first step, it is necessary to align as precisely as possible the vehicle facing the calibration support by means of a laser system so that their respective three-dimensional reference frames are parallel so as to cancel the rotation values while fixing the translation values in three dimensions between the vehicle and the calibration support. This alignment should be done so that the alignment error is less than the calibration tolerance. Then, the lidar acquires at least one image of the calibration medium as a whole in order to determine the values of rotation and translation between the lidar and the calibration marks of the calibration medium. Finally, knowing the rotation and translation values between the vehicle and the calibration support and on the other hand the rotation and translation values between the lidar and the benchmarks of the calibration support, we deduce the values of the extrinsic parameters of calibration of the Lidar which are then stored and used by the vehicle's driving assistance system in order to permanently compensate the Lidar during its use.
[0013] Une telle méthode impose donc un alignement précis du véhicule face au support de calibration ou une mesure de la position du support de calibration par rapport au véhicule, ce qui nécessite du temps et des moyens de mise en œuvre onéreux tels qu’une plateforme d’alignement spécifique, des lasers. Le fait d’utiliser une plateforme d’alignement spécifique impose à déplacer le véhicule en dehors de la ligne de production, ce qui conduit à augmenter les coûts de mise en œuvre. Such a method therefore requires precise alignment of the vehicle facing the calibration support or a measurement of the position of the calibration support relative to the vehicle, which requires time and expensive implementation means such as specific alignment platform, lasers. Using a specific alignment platform requires moving the vehicle off the production line, which leads to increased implementation costs.
[0014] Par conséquent il existe donc un besoin d’un procédé de détermination des valeurs des paramètres extrinsèques à la fois facile et rapide à mettre en œuvre, et sans ajout de contrainte coûteuse de mise en œuvre, tout ayant une calibration extrinsèque fiable du Lidar de sorte que les informations données par les images acquises par le Lidar soient suffisamment fiables et pertinentes pour permettre au système d’assister le conducteur du véhicule. [0014] Consequently there is therefore a need for a method for determining the values of the extrinsic parameters that is both easy and quick to implement, and without adding costly implementation constraints, while having a reliable extrinsic calibration of the Lidar so that the information given by the images acquired by the Lidar is sufficiently reliable and relevant to allow the system to assist the driver of the vehicle.
[0015] En particulier, la solution proposée permet de s’affranchir des contraintes techniques coûteuses telles que l’utilisation d’un système laser pour réaliser un alignement précis entre le véhicule et le support de calibration ou une mesure de la position du support de calibration par rapport au véhicule. In particular, the proposed solution makes it possible to overcome costly technical constraints such as the use of a laser system to produce a precise alignment between the vehicle and the calibration bracket or a measurement of the position of the calibration bracket relative to the vehicle.
Exposé de l’invention Disclosure of the invention
[0016] A cette fin, l’invention a pour objet un procédé de calibration d’un Lidar, à partir d’une mire de calibration, ledit Lidar étant monté sur une zone du véhicule automobile, en vue d’acquérir des images tridimensionnelles de la mire positionnée sur un sol plat, ladite calibration comprenant la détermination des valeurs des paramètres extrinsèques des trois composantes de rotation comprenant l’angle de roulis (roll_L/V), l’angle de tangage (pitch_L/V) et l’angle de lacet (yaw_L/V) entre le repère lié au Lidar (RL) et le repère lié au véhicule (Rv), le procédé de calibration comprenant les étapes suivantes : [0016] To this end, the invention relates to a method for calibrating a Lidar, from a calibration test chart, said Lidar being mounted on an area of the motor vehicle, with a view to acquiring three-dimensional images of the staff positioned on flat ground, said calibration comprising the determination of the values of the extrinsic parameters of the three components of rotation comprising the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the angle yaw (yaw_L / V) between the mark linked to the lidar (RL) and the mark linked to the vehicle (Rv), the calibration process comprising the following steps:
- dans une étape (E1 ), positionner la mire sur le sol plat, ladite mire comprenant au moins trois points de repères non colinéaires, lesdits points de repères étant agencés dans un repère associé à la mire (RM) ; - in a step (E1), positioning the target on the flat ground, said target comprising at least three non-collinear reference points, said reference points being arranged in a reference frame associated with the target (RM);
- dans une étape (E2), déplacer le véhicule selon une trajectoire sensiblement rectiligne en direction de la mire et capturer simultanément au moyen dudit Lidar une série d’images des points de repères ; - in a step (E2), moving the vehicle along a substantially rectilinear path in the direction of the test pattern and simultaneously capturing by means of said Lidar a series of images of the landmarks;
- dans une étape (E3), déterminer une valeur des trois composantes de translation et une valeur des angles de roulis (roll_L/M), de tangage (pitch_L/M) et de lacet (Yaw_L/M) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) à partir d’une image ou un ensemble d’images extraites de ladite série d’images ;- in a step (E3), determine a value of the three translation components and a value of the roll angles (roll_L / M), pitch (pitch_L / M) and yaw (Yaw_L / M) between the reference associated with the Lidar (RL) and the mark associated with the test pattern (RM) from an image or a set of images extracted from said series of images;
- dans une étape (E4), construire la trajectoire du véhicule dans le repère associé à la mire à partir d’un ensemble de valeurs des trois composantes de translation déterminées à l’étape (E3) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) ; - in a step (E4), construct the trajectory of the vehicle in the frame of reference associated with the test pattern from a set of values of the three translation components determined in step (E3) between the frame of reference associated with the lidar (RL) and the mark associated with the staff (RM);
- dans une étape (E5), déterminer une valeur de l’angle de lacet (yaw_V/M) entre le repère associé au véhicule (Rv) et le repère associé à la mire (RM) à partir de la trajectoire du véhicule dans le repère associé à la mire (RM) ; - in a step (E5), determine a value of the yaw angle (yaw_V / M) between the mark associated with the vehicle (Rv) and the mark associated with the test pattern (RM) from the trajectory of the vehicle in the mark associated with the staff (RM);
- dans une étape (E6), déterminer une valeur de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv) à partir de la différence entre la valeur de l’angle de lacet (yaw_V/M) déterminée à l’étape (E5) et la valeur de l’angle de lacet (yaw_L/M) déterminée à l’étape (E3) à partir d’une image ou un ensemble d’images extraites de ladite série d’images ; - in a step (E6), determine a value of the yaw angle (yaw_L / V) between the mark associated with the lidar (RL) and the mark associated with the vehicle (Rv) from the difference between the value of l 'yaw angle (yaw_V / M) determined in step (E5) and the value of the yaw angle (yaw_L / M) determined in step (E3) from a image or a set of images extracted from said series of images;
- dans une étape (E7), déduire les valeurs des trois composantes de rotation de l’angle de roulis (roll_L/V), de l’angle de tangage (pitch_L/V) et de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv). - in a step (E7), deduce the values of the three rotation components of the roll angle (roll_L / V), of the pitch angle (pitch_L / V) and of the yaw angle (yaw_L / V ) between the marker associated with the lidar (RL) and the marker associated with the vehicle (Rv).
[0017] De préférence, le véhicule est positionné à une distance initiale de la mire de calibration supérieure ou égale à un seuil de distance prédéterminé Dmin. Preferably, the vehicle is positioned at an initial distance from the calibration test pattern greater than or equal to a predetermined distance threshold Dmin.
[0018] De préférence, la distance longitudinale Lx entre deux points de repère et la distance latérale Ly entre deux points de repère est égale ou supérieure respectivement à un seuil de distance prédéfini par la résolution dudit Lidar. Preferably, the longitudinal distance Lx between two reference points and the lateral distance Ly between two reference points is respectively equal to or greater than a distance threshold predefined by the resolution of said lidar.
[0019] De préférence, le Lidar est monté à l’avant, à l’arrière ou sur le côté du véhicule, et la mire est positionnée sur le sol plat de sorte qu’elle soit dans le champ de vision du Lidar. [0019] Preferably, the Lidar is mounted at the front, rear or side of the vehicle, and the staff is positioned on the level ground so that it is in the field of view of the Lidar.
[0020] Selon un aspect de l’invention, il est proposé un dispositif de calibration d’un Lidar, tel qu’un Lidar à partir d’une mire de calibration, ledit Lidar étant monté sur une zone du véhicule automobile, en vue d’acquérir des images tridimensionnelles de la mire positionnée sur un sol plat, ladite calibration comprenant la détermination des valeurs des paramètres extrinsèques des trois composantes de rotation comprenant l’angle de roulis (roll_L/V), l’angle de tangage (pitch_L/V) et l’angle de lacet (yaw_L/V) entre le repère lié au Lidar (RL) et le repère lié au véhicule (Rv), ledit dispositif comprenant : According to one aspect of the invention, there is provided a device for calibrating a Lidar, such as a Lidar from a calibration test chart, said Lidar being mounted on an area of the motor vehicle, with a view to to acquire three-dimensional images of the staff positioned on a flat ground, said calibration comprising the determination of the values of the extrinsic parameters of the three components of rotation including the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the yaw angle (yaw_L / V) between the reference linked to the lidar (RL) and the reference linked to the vehicle (Rv), said device comprising:
- une mire de calibration positionnée sur un sol plat, ladite mire comprenant au moins trois points de repères non colinéaires ; a calibration test chart positioned on flat ground, said test target comprising at least three non-collinear reference points;
- un Lidar apte à être monté sur un véhicule et configuré pour générer une série d’images tridimensionnelles de la mire pendant un déplacement rectiligne dudit véhicule sur la portion de sol plat en direction de la mire; - a Lidar capable of being mounted on a vehicle and configured to generate a series of three-dimensional images of the test pattern during a rectilinear movement of said vehicle on the portion of flat ground in the direction of the test target;
- une unité de traitement configurée pour : - a processing unit configured for:
- capturer au moyen dudit du Lidar une série d’images des points de repères pendant le déplacement du véhicule selon une trajectoire sensiblement rectiligne en direction de la mire ; - capture by means of said lidar a series of images of the landmarks during the movement of the vehicle along a substantially rectilinear trajectory in the direction of the staff;
- déterminer une valeur des trois composantes de translation et une valeur des angles de roulis (roll_L/M), de tangage (pitch_L/M) et de lacet (yaw_L/M) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) à partir d’une image ou un ensemble d’images extraites de ladite série d’images ; - determine a value of the three components of translation and a value of the angles of roll (roll_L / M), of pitch (pitch_L / M) and of yaw (yaw_L / M) between the mark associated with the lidar (RL) and the mark associated with the test pattern (RM) from an image or a set of images extracted from said series of images;
- construire la trajectoire du véhicule dans le repère associé à la mire à partir d’un ensemble de valeurs des trois composantes de translation déterminées entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) ; - construct the trajectory of the vehicle in the frame of reference associated with the pattern from a set of values of the three translation components determined between the frame of reference associated with the lidar (RL) and the frame of reference associated with the pattern (RM);
- déterminer une valeur de l’angle de lacet (yaw_V/M) entre le repère associé au véhicule (Rv) et le repère associé à la mire (RM) à partir de la trajectoire du véhicule dans le repère associé à la mire (RM) ; - determine a value of the yaw angle (yaw_V / M) between the reference associated with the vehicle (Rv) and the reference associated with the test pattern (RM) from the trajectory of the vehicle in the reference associated with the sight (RM );
- déterminer une valeur de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv) à partir de la différence entre la valeur de l’angle de lacet (yaw_V/M) entre le repère associé au véhicule et le repère associé à la mire et la valeur de l’angle de lacet (yaw_L/M) entre le repère associé au Lidar et le repère associé à la mire déterminée à partir d’une image ou un ensemble d’images extraites de ladite série d’images ; - determine a value of the yaw angle (yaw_L / V) between the reference associated with the lidar (RL) and the reference associated with the vehicle (Rv) from the difference between the value of the yaw angle (yaw_V / M) between the mark associated with the vehicle and the mark associated with the test pattern and the value of the yaw angle (yaw_L / M) between the mark associated with the lidar and the mark associated with the test pattern determined from an image or a set of images extracted from said series of images;
- déduire des valeurs des trois composantes de rotation de l’angle de roulis (roll_L/V), de l’angle de tangage (pitch_L/V) et de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (RV). - deduce from the values of the three components of rotation of the roll angle (roll_L / V), of the pitch angle (pitch_L / V) and of the yaw angle (yaw_L / V) between the reference associated with the Lidar (RL) and the mark associated with the vehicle (RV).
Brève description des dessins Brief description of the drawings
[0021] D’autres caractéristiques, détails et avantages de l’invention apparaîtront à la lecture de la description détaillée ci-après, et à l’analyse des dessins annexés, sur lesquels : [0021] Other features, details and advantages of the invention will become apparent on reading the detailed description below, and on analyzing the accompanying drawings, in which:
[0022] [Fig. 1 ] La figure 1 illustre schématiquement une vue de dessus du véhicule et du dispositif de calibration des paramètres extrinsèques selon un mode de réalisation de l’invention ; [0022] [Fig. 1] FIG. 1 schematically illustrates a top view of the vehicle and of the device for calibrating the extrinsic parameters according to one embodiment of the invention;
[0023] [Fig. 2] La figure 2 illustre schématiquement le repère (Rv) lié à un véhicule, le repère (RL) lié au dispositif d’imagerie monté sur le pare-brise du véhicule et le repère (RM) lié à la mire de calibration ; [0023] [Fig. 2] FIG. 2 schematically illustrates the mark (Rv) linked to a vehicle, the mark (RL) linked to the imaging device mounted on the windshield of the vehicle and the mark (RM) linked to the calibration test pattern;
[0024] [Fig. 3] La figure 3 illustre schématiquement une vue de dessus de la position du véhicule à deux instants différents pendant son déplacement, montrant la présence d’un angle de lacet yaw_V/M entre le repère (Rv) lié au véhicule et le repère (RM) lié à la mire de calibration ; [0025] [Fig. 4] La figure 4 illustre schématiquement la trajectoire reconstituée du véhicule et l’angle de lacet yaw_V/M entre le repère véhicule et le repère mire calibration déduit à partir de la trajectoire du véhicule dans le repère mire (RM) ; [0024] [Fig. 3] FIG. 3 schematically illustrates a top view of the position of the vehicle at two different times during its movement, showing the presence of a yaw angle yaw_V / M between the mark (Rv) linked to the vehicle and the mark (RM ) linked to the calibration target; [0025] [Fig. 4] FIG. 4 schematically illustrates the reconstructed trajectory of the vehicle and the yaw angle yaw_V / M between the vehicle frame and the calibration target mark deduced from the trajectory of the vehicle in the target frame (RM);
[0026] [Fig. 5] La figure 5 illustre schématiquement un mode de réalisation de l’invention. [0026] [Fig. 5] Figure 5 schematically illustrates one embodiment of the invention.
Description des modes de réalisation Description of the embodiments
[0027] Les dessins et la description ci-après contiennent, pour l’essentiel, des éléments de caractère certain. Ils pourront donc non seulement servir à mieux faire comprendre la présente invention, mais aussi contribuer à sa définition, le cas échéant. [0027] The drawings and the description below contain, for the most part, elements of a certain nature. They can therefore not only serve to better understand the present invention, but also contribute to its definition, if necessary.
[0028] L’invention va maintenant être décrite en référence aux figures 1 à 5. The invention will now be described with reference to Figures 1 to 5.
[0029] En référence à la figure 1 , le dispositif de calibration 10 comprend un Lidar 2 positionné ici sur la figure 1 à l’avant du véhicule, au niveau du pare-chocs et une unité de traitement 4 configurée pour traiter des images tridimensionnelles enregistrées par le Lidar et pour déterminer les paramètres extrinsèques de calibration du Lidar. Dans une autre forme de réalisation, le Lidar peut également être positionné à l’arrière du véhicule. Selon une autre forme de réalisation, le Lidar peut être également monté sur le côté du véhicule. Referring to Figure 1, the calibration device 10 comprises a Lidar 2 positioned here in Figure 1 at the front of the vehicle, at the bumper and a processing unit 4 configured to process three-dimensional images recorded by the Lidar and to determine the extrinsic Lidar calibration parameters. In another embodiment, the lidar can also be positioned at the rear of the vehicle. According to another embodiment, the lidar can also be mounted on the side of the vehicle.
[0030] Le dispositif de calibration 10 est destiné à être utilisé dans un système d’aide à la conduite monté dans le véhicule afin d’assister le conducteur dans sa conduite. Le dispositif 10 de la présente divulgation permet de déterminer les paramètres extrinsèques de calibration du Lidar, à savoir les trois composantes de rotation, l’angle de roulis, de tangage et de lacet du Lidar par rapport au véhicule. [0030] The calibration device 10 is intended for use in a driver assistance system mounted in the vehicle in order to assist the driver in his driving. The device 10 of the present disclosure makes it possible to determine the extrinsic Lidar calibration parameters, namely the three components of rotation, the angle of roll, pitch and yaw of the Lidar with respect to the vehicle.
[0031] Ces paramètres sont utilisés pour améliorer l’interprétation des images tridimensionnelles acquises par le Lidar et permettent ainsi d’assister la conduite de manière plus faible et plus efficace. [0031] These parameters are used to improve the interpretation of the three-dimensional images acquired by the Lidar and thus make it possible to assist driving in a weaker and more efficient manner.
[0032] Selon la présente divulgation, les paramètres extrinsèques déterminés par le dispositif de calibration 10 peuvent également être utilisés pour ajuster le positionnement du Lidar par rapport au véhicule en usine à la fin du processus de fabrication du véhicule de sorte qu’il puisse remplir les critères d’un fonctionnement optimal. A titre d’exemple, dans le cas d’un Lidar longue portée, le fonctionnement optimal correspond à une détection d’un objet situé à une distance de 200 m et dans un champ de vue de ± 10°. According to the present disclosure, the extrinsic parameters determined by the calibration device 10 can also be used to adjust the positioning of the lidar relative to the vehicle at the factory at the end of the vehicle manufacturing process so that it can fulfill the criteria of an operation optimal. By way of example, in the case of a long-range lidar, optimal operation corresponds to detection of an object located at a distance of 200 m and in a field of view of ± 10 °.
[0033] De manière générale, le Lidar est monté dans le pare-chocs du véhicule de manière à observer la route sur laquelle roule le véhicule ainsi que l’environnement du véhicule situé dans le champ de vision du Lidar. [0033] In general, the Lidar is mounted in the bumper of the vehicle so as to observe the road on which the vehicle is traveling as well as the environment of the vehicle located in the field of view of the Lidar.
[0034] De préférence, l’unité de traitement 4 et le Lidar 2 sont mis en oeuvre par une même entité physique. En variante et comme l’illustre la figure 1 , ils peuvent être chacun constitué par une entité physique distincte, reliées entre elles par un lien filaire ou un réseau de communication. Preferably, the processing unit 4 and the lidar 2 are implemented by the same physical entity. As a variant and as shown in Figure 1, they can each be made up of a separate physical entity, interconnected by a wired link or a communication network.
[0035] En outre, le dispositif de calibration comprend une mire 3 qui est positionnée sur le sol plat de manière à être dans le champ de visée du Lidar. Selon l’exemple illustré sur les figures 1 à 3, le Lidar étant à l’avant du véhicule, la mire est positionnée à l’avant du véhicule sur le sol, et agencée de façon que la mire s’étende dans un plan horizontal (XM, YM) formant un repère orthonormé. [0035] In addition, the calibration device comprises a sight 3 which is positioned on the flat ground so as to be in the field of view of the Lidar. According to the example illustrated in Figures 1 to 3, the Lidar being at the front of the vehicle, the sight is positioned at the front of the vehicle on the ground, and arranged so that the sight extends in a horizontal plane. (XM, YM) forming an orthonormal coordinate system.
[0036] Dans le cadre du procédé, un repère lié à la mire, appelé ici repère mire Rm est défini par trois axes XM, YM et ZM. Lors du positionnement de la mire devant le véhicule, les axes de la mire sont pratiquement alignés à quelques degrés de près par rapport aux axes du repère associé au véhicule défini ci-dessous. Après avoir positionné la mire devant le véhicule, l’axe ZM de la mire et l’axe Zv du véhicule sont parallèles. In the context of the method, a frame of reference linked to the test pattern, here called a target mark Rm is defined by three axes XM, YM and ZM. When positioning the sight in front of the vehicle, the axes of the sight are practically aligned to a few degrees of close relative to the axes of the reference mark associated with the vehicle defined below. After positioning the staff in front of the vehicle, the ZM axis of the staff and the Zv axis of the vehicle are parallel.
[0037] La mire comprend un réseau d’au moins trois points de repère 5 disposés à intervalles réguliers alignés suivant l’axe (XM) et suivant l’axe (YM), dans le repère associé à la mire. The target comprises a network of at least three benchmarks 5 arranged at regular intervals aligned along the axis (XM) and along the axis (YM), in the frame associated with the target.
[0038] Selon une forme de réalisation, la distance longitudinale Lx entre deux points de repère suivant l’axe (XM) et la distance latérale Ly entre deux points de repère suivant l’axe (Y) sont égales ou supérieures respectivement à un seuil de distance prédéfini selon la résolution du dispositif d’imagerie. A titre d’exemple, la distance latérale Ly entre deux points est de 0,5m et la distance longitudinale Lx entre deux points est de 1 ,5m. [0039] La mire de calibration est positionnée à une distance initiale D par rapport à l’avant du véhicule qui est égale ou supérieure à un seuil de distance prédéterminé Dmin. Ce seuil de distance est déterminé de sorte que le point de la mire le plus proche du véhicule soit dans le champ de vue du Lidar. A titre d’exemple, la valeur de ce seuil de distance varie entre 4,2 m et 12,5 m lorsque le lidar est pivoté verticalement d’un angle de 4,5° et positionné à une hauteur de 0,5 m par rapport au sol. According to one embodiment, the longitudinal distance Lx between two reference points along the axis (XM) and the lateral distance Ly between two reference points along the axis (Y) are respectively equal to or greater than a threshold distance predefined according to the resolution of the imaging device. By way of example, the lateral distance Ly between two points is 0.5m and the longitudinal distance Lx between two points is 1.5m. The calibration target is positioned at an initial distance D relative to the front of the vehicle which is equal to or greater than a predetermined distance threshold Dmin. This distance threshold is determined so that the point of view closest to the vehicle is in the field of view of the Lidar. For example, the value of this distance threshold varies between 4.2 m and 12.5 m when the lidar is rotated vertically by an angle of 4.5 ° and positioned at a height of 0.5 m by relative to the ground.
[0040] La mire 3 reste fixe pendant la durée de la calibration du Lidar 2. The test chart 3 remains fixed for the duration of the calibration of the lidar 2.
[0041] Comme l’illustre la figure 2, un repère est également lié au véhicule Rv, appelé ici repère véhicule qui est défini par trois axes Xv, Yv et Zv. Par convention, l’axe Xv correspond à la direction horizontale longitudinale du véhicule orienté vers l’avant du véhicule, l’axe Yv correspond à la direction horizontale transversale du véhicule et un troisième axe Zv correspond à la direction verticale du véhicule. Les axes Xv, Yv et Zv ont par convention pour origine le sol. As shown in Figure 2, a mark is also linked to the vehicle Rv, here called a vehicle mark which is defined by three axes Xv, Yv and Zv. By convention, the Xv axis corresponds to the longitudinal horizontal direction of the vehicle facing the front of the vehicle, the Yv axis corresponds to the transverse horizontal direction of the vehicle and a third Zv axis corresponds to the vertical direction of the vehicle. The axes Xv, Yv and Zv originate from the ground by convention.
[0042] Un repère RL propre au Lidar, appelé repère Lidar est défini par trois axes XL, YL et ZL. L’axe XL est l’axe optique du Lidar et est pratiquement parallèle à l’axe Xv. L’axe YL est pratiquement parallèle à l’axe Yv et l’axe ZL est pratiquement parallèle à l’axe Zv. De manière générale, dans le cadre de la présente divulgation, cette condition d’alignement n’est pas nécessaire, il suffit de positionner le Lidar par rapport au véhicule de sorte que la mire soit dans le champ de vue du Lidar. An RL frame specific to the Lidar, called the Lidar frame, is defined by three axes XL, YL and ZL. The XL axis is the optical axis of the Lidar and is practically parallel to the Xv axis. The YL axis is practically parallel to the Yv axis and the ZL axis is practically parallel to the Zv axis. Generally, in the context of the present disclosure, this alignment condition is not necessary, it suffices to position the lidar with respect to the vehicle so that the target is in the field of view of the lidar.
[0043] Le procédé selon la présente divulgation a pour objectif de déterminer les trois angles de rotation permettant de passer du repère Lidar RL au repère véhicule Rv. Les angles de rotation comprennent donc l’angle de roulis, l’angle de tangage et l’angle de lacet qui correspondent respectivement à l’angle de rotation autour de l’axe X, l’angle de rotation autour de l’axe Y et l’angle de rotation autour de l’axe Z. The method according to the present disclosure aims to determine the three angles of rotation making it possible to go from the Lidar RL marker to the Rv vehicle marker. The angles of rotation therefore include the roll angle, the pitch angle and the yaw angle which correspond respectively to the angle of rotation around the X axis, the angle of rotation around the Y axis and the angle of rotation about the Z axis.
[0044] De manière connue, le Lidar est monté sur un support comprenant un axe motorisé pour faire pivoter verticalement suivant l’axe YL la direction d’acquisition d’images du lidar. In known manner, the lidar is mounted on a support comprising a motorized axis for vertically pivoting along the YL axis the direction of acquisition of images of the lidar.
[0045] Le Lidar est configuré pour générer une série d’images de la mire de calibration, notamment pendant un déplacement rectiligne du véhicule sur une portion de sol plat en direction de la mire. Une série d’images comprend donc une succession d’images acquises par le Lidar tout en faisant déplacer le véhicule suivant un mouvement rectiligne. The Lidar is configured to generate a series of images of the calibration pattern, in particular during a rectilinear movement of the vehicle on a portion of flat ground in the direction of the pattern. A series of images therefore includes a succession of images acquired by the Lidar while causing the vehicle to move in a rectilinear movement.
[0046] La série d’images comprend par exemple une première image prise à l’instant t par le Lidar après un premier déplacement du véhicule, une deuxième image prise à l’instant t+1 par le Lidar après un deuxième déplacement du véhicule. The series of images comprises for example a first image taken at time t by the Lidar after a first movement of the vehicle, a second image taken at time t + 1 by the Lidar after a second movement of the vehicle .
[0047] L’unité de traitement 4 est configurée pour recevoir une série d’images de la mire 3 du véhicule acquises par le Lidar et pour déterminer les paramètres extrinsèques de calibration du Lidar. L’unité de traitement est configurée pour déterminer à partir d’au moins deux images extraites de la série d’images les valeurs des paramètres extrinsèques des trois composantes de rotation, à savoir l’angle de roulis (roll_L/V), l’angle de tangage (pitch_L/V) et l’angle de lacet (yaw_L/V) pour passer du repère Lidar (RL) au repère lié au véhicule (Rv). The processing unit 4 is configured to receive a series of images of the test pattern 3 of the vehicle acquired by the Lidar and to determine the extrinsic parameters of the Lidar calibration. The processing unit is configured to determine from at least two images extracted from the series of images the values of the extrinsic parameters of the three components of rotation, namely the roll angle (roll_L / V), the pitch angle (pitch_L / V) and yaw angle (yaw_L / V) to go from the Lidar reference (RL) to the reference linked to the vehicle (Rv).
[0048] L’unité de traitement est configurée pour déterminer les valeurs des trois composantes de translation et les valeurs des angles de roulis (roll_L/M), de tangage (pitch_L/M) et de lacet (yaw_L/M) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) pour chacune des images extraites de la série d’images de la mire de calibration. Ces valeurs sont déterminées selon une méthode de minimisation. The processing unit is configured to determine the values of the three translation components and the values of the roll angles (roll_L / M), pitch (pitch_L / M) and yaw (yaw_L / M) between the reference mark associated with the Lidar (RL) and the mark associated with the test pattern (RM) for each of the images extracted from the series of images of the calibration test pattern. These values are determined using a minimization method.
[0049] La méthode de détermination des valeurs comprend les étapes suivantes :The method of determining the values comprises the following steps:
- extraire d’une image les points de repère 5 ; - extract the reference points 5 from an image;
- déterminer la position 3D de chaque point de repère par rapport une référence mire dans le repère mire, à titre d’exemple le point 0 qui est le premier ; - determine the 3D position of each benchmark relative to a target reference in the target frame, for example point 0 which is the first;
- faire évoluer les paramètres extrinsèques de la projection de sorte que la position 3D de chaque point de repère se rapproche de la position 2D des points extraits par une méthode de minimisation de l’erreur de projection. - change the extrinsic parameters of the projection so that the 3D position of each reference point approaches the 2D position of the points extracted by a projection error minimization method.
[0050] Les paramètres sont déterminés à partir d’un algorithme de descente de gradient de type Levenberg. The parameters are determined from a Levenberg-type gradient descent algorithm.
[0051] En se basant sur l’hypothèse que le véhicule est déplacé selon une trajectoire rectiligne et sur un sol plat, l’angle de roulis (roll_L/M) entre le repère Lidar et le repère mire et l’angle de roulis (roll_L/V) entre le repère lidar et le repère véhicule ont la même valeur. De même l’angle de tangage (pitch_L/M) entre le repère Lidar et le repère mire et l’angle de tangage (pitch_L/V) entre le repère Lidar et le repère véhicule ont la même valeur. Il est noté ici que le déplacement rectiligne du véhicule en direction de la mire ne signifie pas forcément que le déplacement du véhicule est parallèle à un alignement de points de repère 5 de la mire. Based on the assumption that the vehicle is moved along a straight path and on flat ground, the roll angle (roll_L / M) between the Lidar mark and the target mark and the roll angle ( roll_L / V) between the lidar marker and the vehicle marker have the same value. Likewise the pitch angle (pitch_L / M) between the Lidar coordinate system and the target mark and the pitch angle (pitch_L / V) between the Lidar coordinate system and the vehicle coordinate system have the same value. It is noted here that the rectilinear movement of the vehicle in the direction of the target does not necessarily mean that the movement of the vehicle is parallel to an alignment of reference points 5 of the target.
[0052] L’unité de traitement 4 est configurée pour construire la trajectoire du véhicule dans le repère associé à la mire (RM) à partir d’un ensemble de valeurs des trois composantes de translation déterminées pour passer du repère associé au lidar (RL) au repère associé à la mire (RM). Une régression linéaire 3D a été utilisée. The processing unit 4 is configured to build the trajectory of the vehicle in the frame associated with the test pattern (RM) from a set of values of the three translation components determined to go from the frame associated with the lidar (RL ) to the mark associated with the staff (RM). 3D linear regression was used.
[0053] La figure 4 illustre un exemple d’une droite représentative de la trajectoire du véhicule dans le repère mire. En abscisse sont représentées les coordonnées transversales Y et en ordonnée sont représentées les coordonnées longitudinales X. Les différents points représentent les positions relevées du véhicule à différents instants. Il est ainsi possible de déduire l’angle de lacet (yaw_V/M) entre le repère véhicule et le repère mire. Cette déduction est basée sur le fait que quand le véhicule a un mouvement rectiligne droit, la direction du mouvement est colinéaire à l’axe Xv. Ainsi, l’angle de lacet entre l’axe XM et la trajectoire du véhicule correspond à l’angle de lacet entre l’axe XM et l’axe Xv. FIG. 4 illustrates an example of a straight line representative of the trajectory of the vehicle in the target mark. The transverse coordinates Y are represented on the abscissa and the longitudinal coordinates X are represented on the ordinate. The different points represent the positions of the vehicle at different times. It is thus possible to deduce the yaw angle (yaw_V / M) between the vehicle frame and the target frame. This deduction is based on the fact that when the vehicle has a straight rectilinear motion, the direction of motion is collinear with the Xv axis. Thus, the yaw angle between the XM axis and the vehicle path corresponds to the yaw angle between the XM axis and the Xv axis.
[0054] Cet angle est également représenté sur la figure 3 qui illustre la position du véhicule dans le repère mire à deux instants pendant son déplacement selon une trajectoire rectiligne. C’est l’angle entre la droite (di) parallèle à l’axe longitudinale (XM) du repère mire et la droite (d2) représentative de la direction de déplacement du véhicule qui est parallèle à l’axe Xv. This angle is also shown in Figure 3 which illustrates the position of the vehicle in the target mark at two times during its movement along a rectilinear path. This is the angle between the line (di) parallel to the longitudinal axis (XM) of the target mark and the line (d2) representative of the direction of movement of the vehicle which is parallel to the Xv axis.
[0055] L’unité de traitement 4 peut ensuite déterminer une valeur de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv) à partir de la différence entre la valeur de l’angle de lacet (yaw_V/M) entre le repère véhicule et le repère mire et la valeur de l’angle de lacet (yaw_L/M) entre le repère Lidar et le repère mire. La valeur de l’angle de lacet (yaw_L/M) entre le repère Lidar et le repère mire est déterminée à partir d’une image ou un ensemble d’images extraites de la série d’images acquises par le Lidar. [0056] Selon une forme de réalisation avantageuse, il est possible d’obtenir une valeur moyenne de l’angle de lacet (yaw_L/M) entre le repère Lidar et le repère mire à partir d’un ensemble d’images extraites de la série d’images afin d’améliorer la précision de la valeur. The processing unit 4 can then determine a value of the yaw angle (yaw_L / V) between the mark associated with the lidar (RL) and the mark associated with the vehicle (Rv) from the difference between the value of the yaw angle (yaw_V / M) between the vehicle reference and the target mark and the value of the yaw angle (yaw_L / M) between the lidar reference and the target mark. The value of the yaw angle (yaw_L / M) between the Lidar frame and the target frame is determined from an image or a set of images extracted from the series of images acquired by the Lidar. According to an advantageous embodiment, it is possible to obtain an average value of the yaw angle (yaw_L / M) between the Lidar frame and the target frame from a set of images extracted from the series of images to improve the accuracy of the value.
[0057] De manière similaire, il est également possible d’obtenir une valeur moyenne de l’angle de tangage et de l’angle de roulis entre le repère Lidar et le repère véhicule à partir d’un ensemble d’images extraites de de la série d’image afin d’améliorer la précision de ces valeurs. In a similar manner, it is also possible to obtain an average value of the pitch angle and of the roll angle between the Lidar frame and the vehicle frame from a set of images extracted from de the image series to improve the accuracy of these values.
[0058] Ainsi, en déterminant au préalable les trois translations et les trois rotations permettant de passer du repère Lidar au repère mire pour chacune des images extraites d’une série d’images prises par le Lidar et en connaissant la trajectoire du véhicule dans le repère mire, l’unité de traitement permet de déduire les valeurs des trois composantes de rotation de l’angle de roulis (rollJ V), de l’angle de tangage (pitch_L/V) et de l’angle de lacet (yaw_L/V) entre le repère Lidar (RL) et le repère associé au véhicule (Rv). Thus, by determining beforehand the three translations and the three rotations making it possible to go from the Lidar frame to the target frame for each of the images extracted from a series of images taken by the Lidar and by knowing the trajectory of the vehicle in the target mark, the processing unit makes it possible to deduce the values of the three components of rotation of the roll angle (rollJ V), of the pitch angle (pitch_L / V) and of the yaw angle (yaw_L / V) between the Lidar marker (RL) and the marker associated with the vehicle (Rv).
[0059] L’invention va maintenant être décrite dans sa mise en oeuvre. The invention will now be described in its implementation.
[0060] Dans une première étape E1 , on positionne la mire de calibration devant le véhicule. A titre d’exemple, la mire de calibration est positionnée au bout de la ligne de production du véhicule sur un sol plat. In a first step E1, the calibration target is positioned in front of the vehicle. For example, the calibration target is positioned at the end of the vehicle's production line on level ground.
[0061] Le positionnement de la mire est réalisé de sorte que le repère véhicule est sensiblement aligné par rapport au repère mire comme l’illustre la figure 1 et que la mire est dans le champ de visée du Lidar. The positioning of the sight is carried out so that the vehicle mark is substantially aligned with respect to the sight mark as illustrated in FIG. 1 and that the sight is in the field of view of the Lidar.
[0062] Dans une étape E2, le véhicule 1 se déplace selon une trajectoire rectiligne sur une portion de sol plat en direction de la mire selon l’axe (XM) et le Lidar capture simultanément une série d’images des points de repère de la mire. In a step E2, the vehicle 1 moves along a rectilinear path over a portion of flat ground in the direction of the sight along the axis (XM) and the Lidar simultaneously captures a series of images of the landmarks of the sights.
[0063] Dans une étape E3, on détermine selon une méthode connue de minimisation à partir d’une image les valeurs des trois composantes de translation et les valeurs de rotation des angles de roulis (roll_L/M), de tangage (pitch_L/M) et de lacet (yaw_L/M) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM). [0064] Dans le cadre de la présente divulgation, on fait l’hypothèse que le véhicule se déplace selon une trajectoire rectiligne sur un sol plat. Ainsi, les valeurs des angles de rotations déterminées entre le repère Lidar et le repère mire sont constantes. Du fait de la planéité du sol, les valeurs des angles de rotation de tangage et de roulis entre le repère Lidar et le repère mire sont également celles des angles de rotation de tangage et de roulis entre le repère Lidar et le repère véhicule. In a step E3, one determines according to a known minimization method from an image the values of the three components of translation and the values of rotation of the angles of roll (roll_L / M), of pitch (pitch_L / M ) and yaw (yaw_L / M) between the reference associated with the lidar (RL) and the reference associated with the test pattern (RM). In the context of the present disclosure, the assumption is made that the vehicle moves along a rectilinear path on flat ground. Thus, the values of the angles of rotation determined between the lidar frame and the target frame are constant. Due to the flatness of the ground, the values of the pitch and roll rotation angles between the lidar frame and the target frame are also those of the pitch and roll rotation angles between the lidar frame and the vehicle frame.
[0065] Selon une forme de réalisation, l’étape E3 est réalisée uniquement pour une image extraite de ladite série d’images. Ainsi, cette image peut être l’image acquise par le véhicule dans sa position initiale située à une distance D supérieure ou égale à Dmin par rapport au véhicule. [0065] According to one embodiment, step E3 is performed only for an image extracted from said series of images. Thus, this image can be the image acquired by the vehicle in its initial position located at a distance D greater than or equal to Dmin relative to the vehicle.
[0066] Selon une autre forme de réalisation, l’étape E3 est répétée et réalisée pour chacune des images extraites de ladite série d’images. On obtient alors un ensemble de valeurs des trois translations et des trois rotations. A partir de cet ensemble de valeurs, il est donc possible de calculer la moyenne des valeurs des trois angles de rotation. [0066] According to another embodiment, step E3 is repeated and carried out for each of the images extracted from said series of images. We then obtain a set of values of the three translations and the three rotations. From this set of values, it is therefore possible to calculate the average of the values of the three angles of rotation.
[0067] Dans une étape E4, on construit la trajectoire du véhicule dans le repère associé à la mire à partir d’un ensemble de valeurs des trois composantes de translation déterminées entre le repère Lidar (RL) et le repère associé à la mire (RM) déterminés à l’étape de E3 à partir d’au moins deux images. Cette trajectoire est représentée à travers un ensemble de points représentatifs des positions du véhicule lors de son déplacement dans le repère mire comme l’illustre la figure 4. In a step E4, the trajectory of the vehicle is constructed in the frame associated with the test pattern from a set of values of the three translation components determined between the Lidar frame (RL) and the frame associated with the pattern ( RM) determined in step E3 from at least two images. This trajectory is represented through a set of points representative of the positions of the vehicle during its movement in the target mark as illustrated in Figure 4.
[0068] Dans une étape E5, on détermine une valeur de l’angle de lacet (yaw_V/M) entre le repère associé au véhicule (Rv) et le repère associé à la mire (RM) à partir de la trajectoire du véhicule construite à l’étape E4. In a step E5, a value of the yaw angle (yaw_V / M) is determined between the mark associated with the vehicle (Rv) and the mark associated with the test pattern (RM) from the trajectory of the vehicle constructed in step E4.
[0069] Puis dans une étape E6, on détermine une valeur de l’angle de lacet (yaw_LA/) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv) à partir de la différence entre la valeur de l’angle de lacet (yaw_V/M) déterminée à l’étape (E5) et une valeur de l’angle de lacet (yaw_L/M) déterminée à l’étape (E3) pour chacune des images extraites de ladite série d’images ; [0070] Enfin, dans une étape E7, on déduit des valeurs des trois composants de rotation de l’angle de roulis (roll_L/V), de l’angle de tangage (pitch_L/V) et de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv). [0071] Les valeurs des trois composantes de rotation traduisent un désalignement entre le repère lidar et le repère véhicule. La connaissance de ces valeurs permet d’ajuster le positionnement du lidar par rapport au véhicule. Then in a step E6, a value of the yaw angle (yaw_LA /) is determined between the mark associated with the lidar (RL) and the mark associated with the vehicle (Rv) from the difference between the value of the yaw angle (yaw_V / M) determined in step (E5) and a value of the yaw angle (yaw_L / M) determined in step (E3) for each of the images extracted from said series of images; Finally, in a step E7, the values of the three rotation components are deduced from the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the yaw angle ( yaw_L / V) between the reference associated with the lidar (RL) and the reference associated with the vehicle (Rv). The values of the three components of rotation reflect a misalignment between the lidar frame and the vehicle frame. Knowing these values makes it possible to adjust the positioning of the lidar in relation to the vehicle.
[0072] Le procédé de calibration peut avantageusement être réalisé en usine, au bout de la ligne de production en faisant déplacer le véhicule en direction de la mire seulement sur quelques mètres. The calibration process can advantageously be carried out in the factory, at the end of the production line by causing the vehicle to move in the direction of the target only over a few meters.
[0073] L’invention permet de déterminer les paramètres extrinsèques d’un lidar rapidement au moyen d’une mire, aisément et fiable. La mise en oeuvre du procédé de calibration ne nécessite pas l’utilisation d’un système laser pour réaliser un alignement précis entre le véhicule et la mire ou une mesure de la position de la mire par rapport au véhicule. The invention makes it possible to determine the extrinsic parameters of a lidar quickly by means of a test chart, easily and reliably. The implementation of the calibration process does not require the use of a laser system to achieve precise alignment between the vehicle and the staff or to measure the position of the staff relative to the vehicle.
Application industrielle Industrial application
[0074] L’invention peut trouver à s’appliquer notamment dans un système d’assistance à la conduite d’un véhicule automobile. Il est également applicable avantageusement à la calibration d’une caméra ou d’un lidar. [0074] The invention may find application in particular in a system for assisting the driving of a motor vehicle. It is also advantageously applicable to the calibration of a camera or a lidar.

Claims

Revendications Claims
[Revendication 1] Procédé de calibration d’un Lidar (2), à partir d’une mire de calibration (3), ledit Lidar étant monté sur une zone du véhicule automobile (1 ), en vue d’acquérir des images tridimensionnelles de la mire positionnée sur un sol plat, ladite calibration comprenant la détermination des valeurs des paramètres extrinsèques des trois composantes de rotation comprenant l’angle de roulis (roll_L/V), l’angle de tangage (pitch_L/V) et l’angle de lacet (yaw_L/V) entre le repère lié au Lidar (RL) et le repère lié au véhicule (Rv), le procédé de calibration comprenant les étapes suivantes : [Claim 1] Method for calibrating a Lidar (2), from a calibration target (3), said Lidar being mounted on an area of the motor vehicle (1), with a view to acquiring three-dimensional images of the staff positioned on flat ground, said calibration comprising the determination of the values of the extrinsic parameters of the three components of rotation comprising the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the angle of yaw (yaw_L / V) between the mark linked to the lidar (RL) and the mark linked to the vehicle (Rv), the calibration process comprising the following steps:
- dans une étape (E1 ), positionner la mire sur le sol plat, ladite mire comprenant au moins trois points de repères non colinéaires (5) agencés dans un repère associé à la mire (RM) ; - in a step (E1), positioning the target on the flat ground, said target comprising at least three non-collinear reference points (5) arranged in a frame associated with the target (RM);
- dans une étape (E2), déplacer le véhicule selon une trajectoire sensiblement rectiligne en direction de la mire et capturer simultanément au moyen dudit Lidar une série d’images des points de repères ; - in a step (E2), moving the vehicle along a substantially rectilinear path in the direction of the test pattern and simultaneously capturing by means of said Lidar a series of images of the landmarks;
- dans une étape (E3), déterminer une valeur des trois composantes de translation et une valeur des angles de roulis (roll_L/M), de tangage (pitch_L/M) et de lacet (Yaw_L/M) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) à partir d’une image ou un ensemble d’images extraites de ladite série d’images ;- in a step (E3), determine a value of the three translation components and a value of the roll angles (roll_L / M), pitch (pitch_L / M) and yaw (Yaw_L / M) between the reference associated with the Lidar (RL) and the mark associated with the test pattern (RM) from an image or a set of images extracted from said series of images;
- dans une étape (E4), construire la trajectoire du véhicule dans le repère associé à la mire à partir d’un ensemble de valeurs des trois composantes de translation déterminées à l’étape (E3) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) ; - in a step (E4), construct the trajectory of the vehicle in the frame of reference associated with the test pattern from a set of values of the three translation components determined in step (E3) between the frame of reference associated with the lidar (RL) and the mark associated with the staff (RM);
- dans une étape (E5), déterminer une valeur de l’angle de lacet (yaw_V/M) entre le repère associé au véhicule (Rv) et le repère associé à la mire (RM) à partir de la trajectoire du véhicule dans le repère associé à la mire (RM) ; - in a step (E5), determine a value of the yaw angle (yaw_V / M) between the mark associated with the vehicle (Rv) and the mark associated with the test pattern (RM) from the trajectory of the vehicle in the mark associated with the staff (RM);
- dans une étape (E6), déterminer une valeur de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv) à partir de la différence entre la valeur de l’angle de lacet (yaw_V/M) déterminée à l’étape (E5) et la valeur de l’angle de lacet (yaw_L/M) déterminée à l’étape (E3) à partir d’une image ou un ensemble d’images extraites de ladite série d’images ; - in a step (E6), determine a value of the yaw angle (yaw_L / V) between the mark associated with the lidar (RL) and the mark associated with the vehicle (Rv) from the difference between the value of l 'yaw angle (yaw_V / M) determined in step (E5) and the value of the yaw angle (yaw_L / M) determined in step (E3) from an image or a set of images extracted from said series of images;
- dans une étape (E7), déduire les valeurs des trois composantes de rotation de l’angle de roulis (roll_L/V), de l’angle de tangage (pitch_L/V) et de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv). - in a step (E7), deduce the values of the three components of rotation of the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the yaw angle (yaw_L / V) between the reference associated with the lidar (RL) and the reference associated with the vehicle ( Rv).
[Revendication 2] Procédé selon la revendication 1 , dans lequel le véhicule est positionné à une distance initiale de la mire de calibration supérieure ou égale à un seuil de distance prédéterminé Dmin. [Claim 2] The method of claim 1, wherein the vehicle is positioned at an initial distance from the calibration test pattern greater than or equal to a predetermined distance threshold Dmin.
[Revendication 3] Procédé selon la revendication 1 ou 2, dans lequel la distance longitudinale Lx entre deux points de repère et la distance latérale Ly entre deux points de repère est égale ou supérieure respectivement à un seuil de distance prédéfini par la résolution dudit Lidar. [Claim 3] A method according to claim 1 or 2, wherein the longitudinal distance Lx between two landmarks and the lateral distance Ly between two landmarks is respectively equal to or greater than a distance threshold predefined by the resolution of said Lidar.
[Revendication 4] Procédé selon l’une des revendications 1 à 3, dans lequel le Lidar (2) est monté à l’avant, à l’arrière ou sur le côté du véhicule, et la mire (3) est positionnée sur le sol plat de sorte qu’elle soit dans le champ de vision du Lidar. [Claim 4] Method according to one of claims 1 to 3, wherein the lidar (2) is mounted at the front, rear or side of the vehicle, and the staff (3) is positioned on the flat ground so that it is in the Lidar's field of view.
[Revendication 5] Dispositif de calibration (10) d’un Lidar (2), tel qu’un Lidar à partir d’une mire de calibration (3), ledit Lidar étant monté sur une zone du véhicule automobile (1 ), en vue d’acquérir des images tridimensionnelles de la mire positionnée sur un sol plat, ladite calibration comprenant la détermination des valeurs des paramètres extrinsèques des trois composantes de rotation comprenant l’angle de roulis (roll_L/V), l’angle de tangage (pitch_L/V) et l’angle de lacet (yaw_L/V) entre le repère lié au Lidar (RL) et le repère lié au véhicule (Rv), ledit dispositif comprenant : [Claim 5] Device (10) for calibrating a Lidar (2), such as a Lidar from a calibration target (3), said Lidar being mounted on a zone of the motor vehicle (1), in view of acquiring three-dimensional images of the staff positioned on a flat ground, said calibration comprising the determination of the values of the extrinsic parameters of the three components of rotation including the roll angle (roll_L / V), the pitch angle (pitch_L / V) and the yaw angle (yaw_L / V) between the reference linked to the lidar (RL) and the reference linked to the vehicle (Rv), said device comprising:
- une mire de calibration (3) positionnée sur le sol plat, ladite mire comprenant au moins trois points de repères non colinéaires (5) ; - a calibration target (3) positioned on the flat ground, said target comprising at least three non-collinear reference points (5);
- un Lidar (2) apte à être monté sur un véhicule et configuré pour générer une série d’images tridimensionnelles de la mire pendant un déplacement rectiligne dudit véhicule sur le sol plat en direction de la mire; - a Lidar (2) capable of being mounted on a vehicle and configured to generate a series of three-dimensional images of the staff during a rectilinear movement of said vehicle on the flat ground in the direction of the staff;
- une unité de traitement (4) configurée pour : - a processing unit (4) configured for:
- capturer au moyen dudit du Lidar une série d’images des points de repères pendant le déplacement du véhicule selon une trajectoire sensiblement rectiligne en direction de la mire ; - capture by means of said lidar a series of images of the landmarks during the movement of the vehicle along a substantially rectilinear trajectory in the direction of the staff;
- déterminer une valeur des trois composantes de translation et une valeur des angles de roulis (roll_L/M), de tangage (pitch_L/M) et de lacet (yaw_L/M) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) à partir d’une image ou un ensemble d’images extraites de ladite série d’images ; - determine a value of the three components of translation and a value of the angles of roll (roll_L / M), of pitch (pitch_L / M) and of yaw (yaw_L / M) between the mark associated with the lidar (RL) and the mark associated with the test pattern (RM) from an image or a set of images extracted from said series of images;
- construire la trajectoire du véhicule dans le repère associé à la mire à partir d’un ensemble de valeurs des trois composantes de translation déterminées entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) ; - construct the trajectory of the vehicle in the frame of reference associated with the pattern from a set of values of the three translation components determined between the frame of reference associated with the lidar (RL) and the frame of reference associated with the pattern (RM);
- déterminer une valeur de l’angle de lacet (yaw_V/M) entre le repère associé au véhicule (Rv) et le repère associé à la mire (RM) à partir de la trajectoire du véhicule dans le repère associé à la mire (RM) ; - determine a value of the yaw angle (yaw_V / M) between the reference mark associated with the vehicle (Rv) and the reference mark associated with the sight (RM) from the trajectory of the vehicle in the reference mark associated with the sight (RM );
- déterminer une valeur de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv) à partir de la différence entre la valeur de l’angle de lacet (yaw_V/M) entre le repère associé au véhicule (Rv) et le repère associé à la mire (RM) et la valeur de l’angle de lacet (yaw_L/M) entre le repère associé au Lidar (RL) et le repère associé à la mire (RM) déterminée à partir d’une image ou un ensemble d’images extraites de ladite série d’images ; - déduire des valeurs des trois composantes de rotation de l’angle de roulis- determine a value of the yaw angle (yaw_L / V) between the reference associated with the lidar (RL) and the reference associated with the vehicle (Rv) from the difference between the value of the yaw angle (yaw_V / M) between the mark associated with the vehicle (Rv) and the mark associated with the sight (RM) and the value of the yaw angle (yaw_L / M) between the mark associated with the lidar (RL) and the mark associated with the test pattern (RM) determined from an image or a set of images extracted from said series of images; - deduce the values of the three rotation components of the roll angle
(roll_L/V), de l’angle de tangage (pitch_L/V) et de l’angle de lacet (yaw_L/V) entre le repère associé au Lidar (RL) et le repère associé au véhicule (Rv). (roll_L / V), the pitch angle (pitch_L / V) and the yaw angle (yaw_L / V) between the mark associated with the lidar (RL) and the mark associated with the vehicle (Rv).
PCT/EP2021/050518 2020-02-03 2021-01-13 Method for calibrating the extrinsic characteristics of a lidar WO2021156026A1 (en)

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