CN116990787B - Scanning platform coordinate system error correction method based on airborne laser radar system - Google Patents
Scanning platform coordinate system error correction method based on airborne laser radar system Download PDFInfo
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- 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
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- G—PHYSICS
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
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Abstract
The invention discloses a scanning platform coordinate system error correction method based on an airborne laser radar system, which belongs to the technical field of laser radar measurement and is used for error correction of the airborne laser radar system, and comprises the steps of carrying the airborne laser radar system on a horizontally advancing crane, enabling the crane to be in a static horizontal suspension state, and vertically calibrating the rotation center of a reflecting mirror downwards; turning on a laser transceiver and a rotating mirror scanning device, reflecting a laser scanning track downwards, and carrying out fixed point calibration on the long and short axis vertexes of the actual oval scanning track according to the actual laser scanning track in a site coordinate system; and processing the rotational distortion, the tensile distortion and the translational distortion to obtain a scanning platform coordinate system error correction formula. The invention corrects the scanning coordinate by the correction equation, thereby realizing the correction and compensation of the influence of the structural error, and the coordinate precision of the laser foot point space coordinate obtained under the corrected scanning platform coordinate system is improved.
Description
Technical Field
The invention discloses a scanning platform coordinate system error correction method based on an airborne laser radar system, and belongs to the technical field of laser radar measurement.
Background
With the expansion of social demands and the breakthrough of laser radar related technologies, airborne laser radar detection has been developed into an emerging high-tech. The airborne laser radar detection system is used as a complex system with high integration of multiple sensors, can be carried on an unmanned plane platform, and can realize three-dimensional inversion of topography and topography by carrying out fusion processing on data acquired by the multiple sensors. The advantages of short working period and less detection scene limit of the airborne laser radar are that the detection work in shallow sea, island or ship can not enter the sea area is incomparable. In order to be better applied to practical scenes, the circular mirror off-axis type ocean laser radar is used for carrying out scanning detection work, and a detection system of the circular mirror off-axis type ocean laser radar is more prone to be miniaturized and light in development direction, so that all mechanical devices are required to be installed by fully utilizing the inner space. However, in the process of machining and device installation, some systematic errors are inevitably caused, so that errors exist between the actual laser reflected light direction and the design direction, errors exist in the generated laser foot points and point cloud coordinates, and the accuracy of inverted three-dimensional topographic data is affected. In the currently disclosed airborne laser radar error checking literature, most of the error checking literature is used for checking the largest systematic error source placement error, and the error of a sighting axis caused by the installation of a rotating shaft of a driving motor and a scanning rotating mirror is rarely checked, or the error of an airborne laser scanning platform is rarely checked. However, the alignment axis error generated by the installation is fixed and unchanged, and the influence on the detection precision of the airborne laser radar is increased along with the increase of the working height of the laser radar. In order to fully improve the detection precision of the laser radar and generate accurate point cloud data, the calibration of the collimation axis error is necessary and has important significance.
In a circular mirror off-axis type ocean laser radar device, an included angle between a normal line of a reflecting mirror and a rotating shaft of a driving motor is usually designed to be 7.5 degrees, an included angle between the rotating shaft of the driving motor and a horizontal line is designed to be 45 degrees, and laser is horizontally incident and is positioned on or parallel to a vertical plane where the rotating shaft of the driving motor is positioned. However, when the mechanical device is installed, the installation included angle and the parallel precision of incident light cannot be strictly controlled, and the error of the actual installation angle and the position leads to the error between the laser foot point coordinate obtained under the actual scanning platform coordinate system and the laser foot point coordinate obtained under the ideal scanning platform coordinate system, so that the distortion of the point cloud is finally caused. Most laser radar error checking is to check the largest systematic error placement error, and the calibration axis error caused by mechanical installation is rarely checked, however, the data error caused by the calibration axis error cannot be corrected through the placement error checking procedure. Based on the method, the calibration of the alignment axis error is needed before the test, the alignment axis error of the detection system is reversely calculated through the distortion analysis of the actual scanning track and the theoretical track, a scanning platform error equation is constructed to calibrate the scanning platform coordinate, and the accurate laser foot point coordinate is generated under the corrected scanning coordinate system.
Disclosure of Invention
The invention aims to provide a scanning platform coordinate system error correction method based on an airborne laser radar system, so as to solve the problem of placement errors of the airborne laser radar system in the prior art.
The scanning platform coordinate system error correction method based on the airborne laser radar system comprises the following steps:
B1. the method comprises the steps of carrying an airborne laser radar system on a horizontally advancing crane, wherein the crane is in a static horizontal suspension state, and vertically calibrating the rotation center of a reflector downwards;
B2. turning on a laser transceiver and a rotating mirror scanning device, reflecting a laser scanning track downwards, and carrying out fixed point calibration on the long and short axis vertexes of the actual oval scanning track according to the actual laser scanning track in a site coordinate system;
B3. processing rotational distortion;
B4. processing stretching distortion;
B5. processing translational distortion;
B6. and obtaining a scanning platform coordinate system error correction formula.
B1 bagThe method comprises the following steps: calibration point as origin of coordinates O 2 The straight line along the horizontal advancing direction of the crane is Y 2 An axis passing through the origin and perpendicular to Y 2 The straight line of the axis is X 2 The straight line of the axis, the origin and the rotation center of the reflector is Z 2 Shaft, build O 2 -X 2 Y 2 Z 2 A field coordinate system, a laser scanning track is in Y 2 The axis is a long axis b, and the Y positive half axis is b 1 The negative half shaft is b 2 At X 2 The axis is a short axis a, and the X positive half axis is a 1 The negative half shaft is a 2 。
B2 comprises:
the long axis of the actual scanning track is measured as b ', the short axis is measured as a', and the intersection point of the long axis and the short axis is measured as the actual origin O 2 ' obtaining the origin coordinate in the site coordinate systemTwo long axis vertex coordinates->And->Two short axis vertex coordinates->And->。
B3 comprises:
site coordinate system O 2 -X 2 Y 2 Z 2 Based on the vectorAnd->Obtaining the included angle +.>：
；
Will be the site coordinate system O 2 -X 2 Y 2 Z 2 Around Z 2 Shaft rotation W 1 Realizes the correction of the rotation distortion quantity, and the rotation distortion correction matrix is that：
；
After rotational distortion correction, the image is corrected along X 2 Axis movement X 0 Distance along Y 2 Axis movement Y 0 Distance along Z 2 Axial movement Z 0 Distance-derived translational distortion correction parameter X 0 、Y 0 And Z.
B4 comprises:
drawing a long-short axis coordinate graph according to 5 coordinate points of a known origin and a long-short axis vertex in a site coordinate system, wherein two axes are intersected to form the origin, drawing an ideal long-short axis graph and an actual long-short axis graph with equal specifications, intersecting the ideal long-short axis to form a rectangular plan graph, intersecting the actual long-short axis to form a parallelogram plan graph, and carrying out binarization treatment on the two graphs;
and (3) performing edge detection on the binarized image in two directions of horizontal and vertical by utilizing a Sobel operator, and then solving the inclination angles in the two directions of horizontal and vertical by using Radon transformation on the basis of the edge detection.
B4 comprises: obtaining the stretching distortion between the actual long-short axis image and the ideal long-short axis image by using Radon transformation, and obtaining the horizontal inclination angle W of the image 2 And vertical tilt angle W 3 Establishing a rotation matrix to perform error correction on an ideal coordinate system;
the resulting horizontal tilt angle W 2 Correcting the rotation matrix to be the rotation angle around the Y axis of the scanning platform coordinate systemThe resulting vertical tilt angle W 3 For the rotation angle of the scanning platform coordinate system around the X-axis, the rotation matrix is corrected to +.>：
； />。
B4 comprises:
the horizontal tilt angle algorithm is calculated by Radon transformation:
t1, assuming that the horizontal inclination range of an image is 0-180 degrees, projecting the image subjected to horizontal edge detection at 0-180 degrees by using Radon transformation;
t2, obtaining an angle θ1 when the addition of the non-zero values after projection reaches the maximum;
t3. the horizontal tilt angle of the image should be the complement of θ1, and subtracting θ1 from 90 ° will obtain the horizontal tilt angle W of the image 2 。
B4 comprises:
the vertical tilt algorithm using Radon transform is:
the method comprises the steps that M1, assuming that the vertical inclination range of an image is-45 degrees, carrying out projection on the image subjected to horizontal edge detection at-45 degrees by using Radon transformation;
m2, obtaining an angle theta 2 when the addition of the non-zero values after projection reaches the maximum;
m3, the vertical inclination range of the image is-45 degrees to 45 degrees, and the vertical inclination angle W of the image is obtained by subtracting 45 degrees from theta 2 3 。
B5 comprises:
site coordinate system O 2 -X 2 Y 2 Z 2 The ideal origin isConnecting the long axis vertex with the short axis vertex to obtain two straight line foot points +.>The actual origin +.>Performing rotation and stretching distortion to obtain translational distortion parameters:
；
in the method, in the process of the invention,for corrected actual origin coordinates, +.>In order to rotate the matrix is rotated,the actual origin coordinates are uncorrected.
B6 comprises:
an error correction formula is carried out on an ideal scanning platform:
；
wherein,for uncorrected coordinates in the ideal scanning platform coordinate system, +.>For the translation correction parameter +.>For rotating matrix +.>The corrected ideal coordinate system coordinates;
performing precision evaluation by using the corrected ideal coordinate system coordinates, and outputting a scanning platform error calibration equation if the calibration difference is smaller than a set precision threshold; if the correction difference is larger than the set precision threshold, carrying out secondary correction on the basis of the corrected scanning platform, drawing a coordinate graph of the long and short axis coordinates and the actual long and short axis coordinates under the corrected scanning platform, and generating a plane binarization image until the correction value of the obtained coordinates and the actual coordinates is smaller than the set precision threshold under the corrected scanning platform, and meeting the precision requirement:
；
in the method, in the process of the invention,for (I)>For (I)>Is that;
during secondary correction, scanning a platform error correction equation:
；
and (3) scanning a platform error correction equation during n times of correction:
；
in the secondary correction type, the correction amount is set,for correcting the coordinates in the scanning platform coordinate system once, +.>Correction parameters for secondary translation, < >>Is a quadratic rotation matrix +.>Is the ideal coordinate after the secondary correctionCoordinates;
in the n-time correction type, the correction is performed,correcting the coordinates of the scanning platform in the coordinate system for n-1 times,/for>Correction parameters for n translations,>for n rotation matrices +.>And the coordinates of the ideal coordinate system after n times of correction are the coordinates which finally meet the precision requirement and the error correction equation of the scanning platform.
Compared with the prior art, the invention has the following beneficial effects: and measuring the actual laser scanning track, reversely analyzing and correcting the structural errors, and generating an error correction equation. And correcting and compensating the influence of the structural errors by correcting the scanning coordinates through a correction equation. The coordinate precision of the laser foot point space coordinate obtained under the corrected scanning platform coordinate system is improved.
Drawings
FIG. 1 is a technical flow chart of the present invention;
FIG. 2 is a diagram of a laser scanning stage coordinate system;
FIG. 3 is a schematic illustration of a test;
FIG. 4 is an idealized scan trajectory graph;
FIG. 5 is an actual scan trajectory graph;
FIG. 6 is a diagramAn original image and a Radon transformation coordinate system diagram;
FIG. 7 is a schematic diagram of a preferred embodiment of the present inventionParallel to->Linear integral plot of the axis.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The scanning platform coordinate system error correction method based on the airborne laser radar system comprises the following steps:
B1. the method comprises the steps of carrying an airborne laser radar system on a horizontally advancing crane, wherein the crane is in a static horizontal suspension state, and vertically calibrating the rotation center of a reflector downwards;
B2. turning on a laser transceiver and a rotating mirror scanning device, reflecting a laser scanning track downwards, and carrying out fixed point calibration on the long and short axis vertexes of the actual oval scanning track according to the actual laser scanning track in a site coordinate system;
B3. processing rotational distortion;
B4. processing stretching distortion;
B5. processing translational distortion;
B6. and obtaining a scanning platform coordinate system error correction formula.
B1 comprises: calibration point as origin of coordinates O 2 The straight line along the horizontal advancing direction of the crane is Y 2 An axis passing through the origin and perpendicular to Y 2 The straight line of the axis is X 2 The straight line of the axis, the origin and the rotation center of the reflector is Z 2 Shaft, build O 2 -X 2 Y 2 Z 2 A field coordinate system, a laser scanning track is in Y 2 The axis is a long axis b, and the Y positive half axis is b 1 The negative half shaft is b 2 At X 2 The axis is a short axis a, and the X positive half axis is a 1 The negative half shaft is a 2 。
B2 comprises:
measuring the long axis b 'and the short axis a' of the actual scanning track, and the lengthThe short axis intersection point is the actual origin O 2 ' obtaining the origin coordinate in the site coordinate systemTwo long axis vertex coordinates->And->Two short axis vertex coordinates->And->。
B3 comprises:
site coordinate system O 2 -X 2 Y 2 Z 2 Based on the vectorAnd->Obtaining the included angle +.>：
；
Will be the site coordinate system O 2 -X 2 Y 2 Z 2 Around Z 2 Shaft rotation W 1 Realizes the correction of the rotation distortion quantity, and the rotation distortion correction matrix is that：
；
After rotational distortion correction, the image is corrected along X 2 Axis movement X 0 Distance along Y 2 Axis movement Y 0 Distance along Z 2 Axial movement Z 0 Distance-derived translational distortion correction parameter X 0 、Y 0 And Z.
B4 comprises:
drawing a long-short axis coordinate graph according to 5 coordinate points of a known origin and a long-short axis vertex in a site coordinate system, wherein two axes are intersected to form the origin, drawing an ideal long-short axis graph and an actual long-short axis graph with equal specifications, intersecting the ideal long-short axis to form a rectangular plan graph, intersecting the actual long-short axis to form a parallelogram plan graph, and carrying out binarization treatment on the two graphs;
and (3) performing edge detection on the binarized image in two directions of horizontal and vertical by utilizing a Sobel operator, and then solving the inclination angles in the two directions of horizontal and vertical by using Radon transformation on the basis of the edge detection.
B4 comprises: obtaining the stretching distortion between the actual long-short axis image and the ideal long-short axis image by using Radon transformation, and obtaining the horizontal inclination angle W of the image 2 And vertical tilt angle W 3 Establishing a rotation matrix to perform error correction on an ideal coordinate system;
the resulting horizontal tilt angle W 2 Correcting the rotation matrix to be the rotation angle around the Y axis of the scanning platform coordinate systemThe resulting vertical tilt angle W 3 For the rotation angle of the scanning platform coordinate system around the X-axis, the rotation matrix is corrected to +.>：
； />。
B4 comprises:
the horizontal tilt angle algorithm is calculated by Radon transformation:
t1, assuming that the horizontal inclination range of an image is 0-180 degrees, projecting the image subjected to horizontal edge detection at 0-180 degrees by using Radon transformation;
t2, obtaining an angle θ1 when the addition of the non-zero values after projection reaches the maximum;
t3. the horizontal tilt angle of the image should be the complement of θ1, and subtracting θ1 from 90 ° will obtain the horizontal tilt angle W of the image 2 。
B4 comprises:
the vertical tilt algorithm using Radon transform is:
the method comprises the steps that M1, assuming that the vertical inclination range of an image is-45 degrees, carrying out projection on the image subjected to horizontal edge detection at-45 degrees by using Radon transformation;
m2, obtaining an angle theta 2 when the addition of the non-zero values after projection reaches the maximum;
m3, the vertical inclination range of the image is-45 degrees to 45 degrees, and the vertical inclination angle W of the image is obtained by subtracting 45 degrees from theta 2 3 。
B5 comprises:
site coordinate system O 2 -X 2 Y 2 Z 2 The ideal origin isConnecting the long axis vertex with the short axis vertex to obtain two straight line foot points +.>The actual origin +.>Performing rotation and stretching distortion to obtain translational distortion parameters:
；
in the method, in the process of the invention,for corrected actual origin coordinates, +.>In order to rotate the matrix is rotated,the actual origin coordinates are uncorrected.
B6 comprises:
an error correction formula is carried out on an ideal scanning platform:
；
wherein,for uncorrected coordinates in the ideal scanning platform coordinate system, +.>For the translation correction parameter +.>For rotating matrix +.>The corrected ideal coordinate system coordinates;
performing precision evaluation by using the corrected ideal coordinate system coordinates, and outputting a scanning platform error calibration equation if the calibration difference is smaller than a set precision threshold; if the correction difference is larger than the set precision threshold, carrying out secondary correction on the basis of the corrected scanning platform, drawing a coordinate graph of the long and short axis coordinates and the actual long and short axis coordinates under the corrected scanning platform, and generating a plane binarization image until the correction value of the obtained coordinates and the actual coordinates is smaller than the set precision threshold under the corrected scanning platform, and meeting the precision requirement:
；
in the method, in the process of the invention,for (I)>For (I)>Is that;
during secondary correction, scanning a platform error correction equation:
；
and (3) scanning a platform error correction equation during n times of correction:
；
in the secondary correction type, the correction amount is set,for correcting the coordinates in the scanning platform coordinate system once, +.>Correction parameters for secondary translation, < >>Is a quadratic rotation matrix +.>The ideal coordinate system coordinate after the secondary correction;
in the n-time correction type, the correction is performed,correcting the coordinates of the scanning platform in the coordinate system for n-1 times,/for>Correction parameters for n translations,>for n rotation matrices +.>After n times of correctionThe ideal coordinate system coordinates of the scanning platform, namely the coordinates which finally meet the precision requirement and the scanning platform error correction equation.
The technical process of the invention is shown in figure 1, and comprises the steps of obtaining the origin and vertex coordinates of an actual oval scanning track oval, setting an accuracy threshold value, judging that the accuracy threshold value is larger than the accuracy threshold value, generating a binarization image, performing sobel operator edge detection, performing radon transformation to obtain an inclined angle, performing scanning platform coordinate correction, calculating the vertex coordinates of a laser corner point, obtaining the origin and vertex coordinates of a design and oval scanning track oval, re-executing the distortion of the scanning track, judging that the distortion is smaller than the accuracy threshold value, and outputting a final error correction equation.
The experimental process of the invention is schematically shown in figure 3, and the formula is obtained according to the scanning angle in the calculation flowWhen the mirror normal lies in the optical path plane, the mirror angle +.>Or->The scan angle reaches a maximum +.>The long axis solving formula is +.>When the mirror is at angle +>Or->The scan angle reaches a minimum +.>The short axis is calculated as +.>。
In the step B2, distortion such as rotation, translation and stretching exists between the actual scanning track and the ideal scanning track, and the structural error existing in the ideal laser scanning platform is reversely calculated through the distortion of the actual scanning track. In B3, when the motor rotating shaft and the reflecting rotating mirror are installed, the motor rotating shaft is not coplanar with an ideal scanning coordinate system OYZ, and an error angle exists between the motor rotating shaft and the reflecting rotating mirror, so that a laser scanning track is positioned at O 2 X 2 Y 2 The plane generates rotational distortion. In B4, when the motor rotating shaft and the reflecting rotating mirror are installed, the actual value of the included angle between the installed motor rotating shaft and the reflecting rotating mirror is not equal to the design value, so that the laser scanning track is in O 2 X 2 Y 2 The plane creates a tensile distortion. The stretching distortion tilting modes include horizontal tilting, vertical tilting and mixed tilting. Because of the uncertainty of the installation, there may be a mixed tilt distortion, so the calibration needs to take into account both horizontal and vertical corrections.
The Sobel operator performs edge detection on the binarized image in both the horizontal and vertical directions. The Sobel operator is to take a certain pixel point as a center, perform weighting operation of pixel values in a neighborhood range of the pixel point, judge whether the point is in an extremum state, and if the point is in the extremum state, the point is an image edge. Its advantages are simple calculation and high speed.
The specific implementation is as follows:representation dot->Is a pixel value of (a). />For->A gradient in the horizontal direction for detecting horizontal edges. />Is calculated as follows:
；
for->A gradient in the vertical direction is used to detect vertical edges. />Is calculated as follows:
；
setting a threshold t=1 by comparing the threshold withIs to judge +.>Whether it is an edge point. Setting a threshold value as +_for each pixel point in the image when detecting the horizontal edge>Average of squares of (c). Setting a threshold value to +_for each pixel in the image when detecting vertical edges>Average of squares of (c). If the threshold ratio->Little->Is an edge point.
And calculating the inclination angle of the image by adopting Radon transformation, wherein the Radon transformation refers to the projection of the image in a certain angle direction, and the angle corresponding to the projection distance when the projection distance is at the extreme value is the inclination angle of the image. Image smudging or imbalance does not affect Radon transformThe resulting tilt angle. Due to the influence of the actual installation positions of the motor rotating shaft and the reflecting rotating mirror, the position of the motor rotating shaft is equal to the position of the reflecting rotating mirror 2 X 2 Y 2 In plan, the long and short axes of the oval scan trajectory may form a parallelogram plane, as shown in fig. 4 and 5. The actual deformation is detected and corrected step by step, firstly, horizontal rotation correction is carried out, the horizontal rotation angle is detected, and correction is carried out by rotating the image. For the miscut deformation in the vertical direction, detecting an error cutting angle, and carrying out miscut correction by using affine transformation.
The projection calculation formula generated by the two-dimensional Radon transformation is as follows:
；
wherein:
；
in the method, in the process of the invention,for ideal long and short axis map coordinates, < >>For the actual long-short axis map coordinates, < >>Is the tilt angle.
The Radon transform of (2) is shown in FIG. 6, FIG. 6 is +.>A coordinate system generated by Radon transformation. FIG. 7 is->Parallel to->Of shaftsLinear integration. When->In the case of an image matrix, radon transformation refers to the projection of the image matrix at a certain angle.
B5, according to the ideal originAnd the corrected actual origin->According to the position coordinates of the two points, the translational distortion of the image is intuitively reflected. B6, obtaining a rotation angle W through rotation distortion correction 1 Obtaining a translation amount X through translation distortion correction 0 、Y 0 Obtaining a rotation angle W through stretching distortion correction 2 、W 3 . And correcting the ideal scanning platform coordinate system through the obtained correction parameters, and obtaining the actual scanning platform coordinate system which accords with the actual conditions through parameter correction.
In the step B6, the obtained error correction equation is used for checking an ideal scanning platform coordinate system, error correction is carried out on the laser foot point coordinates obtained under the scanning platform, the corrected long and short axis coordinates and the actual long and short axis coordinates are checked, and if the checking difference is smaller than a set precision threshold, the scanning platform error checking equation is output; if the correction difference is larger than the set precision threshold, correcting again on the basis of the corrected scanning platform, drawing a coordinate graph of the corrected scanning platform and the actual long and short axis coordinates, generating a plane binarization image, repeating the steps until the correction value of the obtained coordinates and the actual coordinates is smaller than the set precision threshold under the corrected scanning platformThe precision requirement is met.
The scanning platform coordinate system error correction method based on the airborne laser radar system carries out laser foot point space coordinate calculation and comprises the following steps:
s1, establishing a laser scanning platform coordinate system and an auxiliary coordinate system, wherein the laser scanning platform coordinate system is shown in FIG. 2;
s2, acquiring distance data through an airborne laser radar detection systemHAnd turning mirror cornerThrough distanceHAnd corner->Obtaining the space coordinates of the laser foot points;
s3, analyzing the influence of the sight axis error, utilizing the proportional relation between the error influence degree and the operation height, amplifying the influence of the structural error on the laser scanning track after the laser radar reaches the fixed height, and reversely analyzing and correcting the structural error existing in the detection and correction process by measuring the actual laser scanning track to generate an error correction equation; correcting and compensating the scanning coordinates through a correction equation to realize correction and compensation of influence caused by structural errors; and obtaining the space coordinates of the laser foot points under the corrected scanning platform coordinate system, and improving the coordinate precision.
S1 comprises the following steps: establishing a laser scanning platform coordinate system by taking the rotation center of the reflecting mirror as a coordinate origin O, wherein a Y axis is the advancing direction of the laser radar carrier, a Z axis is vertical upwards, and an X axis is vertical to a Y, Z axis, so as to form a right-hand coordinate system O-XYZ;
counter-rotating with X-axis as rotation axis to form X 1 An axis, at this time, corresponding to Z 1 The shaft coincides with the rotating shaft of the driving motor to construct an auxiliary coordinate system O-X 1 Y 1 Z 1 The auxiliary coordinate system takes the rotation center of the reflector as the origin of coordinates O, Y 1 The axis is the advancing direction of the laser radar carrier, Z 1 The shaft is the rotating shaft of a driving motor, X 1 Axis and Y 1 、Z 1 The axis is vertical, and forms a right-hand coordinate system O-X 1 Y 1 Z 1 。
S2 comprises the following steps: in the laser radar device, the included angle between the normal line of the reflecting mirror and the rotating shaft of the driving motor is designed to beIn one embodiment, the method, in one embodiment,7.5 degrees, the included angle between the rotating shaft of the driving motor and the horizontal line is +.>In the examples, < >>45 degrees, the laser is horizontally incident and is positioned on or parallel to the vertical plane where the rotating shaft of the driving motor is positioned;
s2.1. in auxiliary coordinate System O-X 1 Y 1 Z 1 In (1), an incident light direction vector F1 is obtained:
；
mirror normal vector F2:
；
according to the vector angle formula, the angle between the incident light and the normal of the reflecting mirrorThe method comprises the following steps:
；
。
s2.2, when the incident light of the laser, the normal line of the reflecting mirror and the three lines of the reflected light of the laser are coplanar, the plane where the laser is located is called as the plane of the optical path, and the normal vector of the plane of the optical path is obtained under an auxiliary coordinate systemThe method comprises the following steps:
；
；
known incident ray F1, mirror normal F2 and optical path plane normalAnd the position relation between the reflection light F3 and the reflection light F3 is established, and the relation is solved:
。
s2.3. reflecting light F3 from auxiliary coordinate system O 1 -X 1 Y 1 Z 1 Rotation transitions to the laser scanning stage coordinate system O-XYZ, where the reflected light unit vector is in the O-XYZ coordinate systemThe method comprises the following steps:
；
wherein,is the direction cosine of the reflected light vector, +.>Indicating that the reflected light F3 thus obtained is rotated about the X-axis in opposite directions +.>。
S2.4, the included angle between the reflected light and the vertical downward direction is a scanning angle, and the scanning angle is also a zenith angle：
；
Representation->Is about->Is a function of (2);
the central rotation angle of the laser on the plane is the azimuth angle：
；
Representation->Is about->Is a function of (2);
spatial coordinates of laser foot pointsThe method comprises the following steps:
；
in the method, in the process of the invention,、/>、/>coordinate values representing three dimensions of the spatial coordinates of the laser foot point;
distance for laser foot point space coordinatesHZenith angleq() And azimuth y ()>) The process is expressed as follows:
。
under an ideal scanning platform coordinate system, the obtained laser foot point space coordinate is the coordinate under an ideal design value. However, when the motor rotating shaft and the reflecting rotating mirror are installed, due to uncertainty of an installation process, perfect installation cannot be performed according to a design value, so that an included angle A between the normal line of the reflecting mirror and the rotating shaft of the driving motor and an included angle B between the rotating shaft of the driving motor and the horizontal line of the driving motor are not equal to set angles of 7.5 degrees and 45 degrees to a certain extent, and errors exist between the design value and an actual value. The error is fixed and does not change along with the motion state, so that the error exists in the calculation of the space coordinates of the laser foot points, and the degree of error is increased along with the increase of the working height of the laser radar. Therefore, it is necessary to complete the calibration of this error before the lidar test, generating a correction equation.
However, due to uncertainty of the mounting process, the feasibility of directly detecting the resulting error caused by the mounting process is not great, and the measurement is very difficult. According to the invention, the influence of the structural error on the laser scanning track is amplified after the laser radar reaches the fixed height by utilizing the proportional relation between the error influence degree and the operation height.
；
；/>Is the total rotation matrix;
；
；
then；
In the method, in the process of the invention,is an intermediate parameter.
The above embodiments are only for illustrating the technical aspects of the present invention, not for limiting the same, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may be modified or some or all of the technical features may be replaced with other technical solutions, which do not depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (4)
1. The scanning platform coordinate system error correction method based on the airborne laser radar system is characterized by comprising the following steps of:
B1. the method comprises the steps of carrying an airborne laser radar system on a horizontally advancing crane, wherein the crane is in a static horizontal suspension state, and vertically calibrating the rotation center of a reflector downwards;
B2. turning on a laser transceiver and a rotating mirror scanning device, reflecting a laser scanning track downwards, and carrying out fixed point calibration on the long and short axis vertexes of the actual oval scanning track according to the actual laser scanning track in a site coordinate system;
B3. processing rotational distortion;
B4. processing stretching distortion;
B5. processing translational distortion;
B6. obtaining a scanning platform coordinate system error correction formula;
b3 comprises:
site coordinate system O 2 -X 2 Y 2 Z 2 Based on the vectorAnd->Obtaining the included angle +.>：
；
Will be the site coordinate system O 2 -X 2 Y 2 Z 2 Around Z 2 Shaft rotation W 1 Realizes the correction of the rotation distortion quantity, and the rotation distortion correction matrix is that：
；
After rotational distortion correction, the image is corrected along X 2 Axis movement X 0 Distance along Y 2 Axis movement Y 0 Distance along Z 2 Axial movement Z 0 Distance-derived translational distortion correction parameter X 0 、Y 0 And Z;
b4 comprises:
drawing a long-short axis coordinate graph according to 5 coordinate points of a known origin and a long-short axis vertex in a site coordinate system, wherein two axes are intersected to form the origin, drawing an ideal long-short axis graph and an actual long-short axis graph with equal specifications, intersecting the ideal long-short axis to form a rectangular plan graph, intersecting the actual long-short axis to form a parallelogram plan graph, and carrying out binarization treatment on the two graphs;
performing edge detection on the binary image in two directions, namely horizontal and vertical directions by utilizing a Sobel operator, and then solving the inclination angles in the two directions by using Radon transformation on the basis of the edge detection;
b4 comprises: obtaining the stretching distortion between the actual long-short axis image and the ideal long-short axis image by using Radon transformation, and obtaining the horizontal inclination angle W of the image 2 And vertical tilt angle W 3 Establishing a rotation matrix to perform error correction on an ideal coordinate system;
the resulting horizontal tilt angle W 2 Correcting the rotation matrix to be the rotation angle around the Y axis of the scanning platform coordinate systemThe resulting vertical tilt angle W 3 For the rotation angle of the scanning platform coordinate system around the X-axis, the rotation matrix is corrected to +.>：
； />；
B4 comprises:
the horizontal tilt angle algorithm is calculated by Radon transformation:
t1, assuming that the horizontal inclination range of an image is 0-180 degrees, projecting the image subjected to horizontal edge detection at 0-180 degrees by using Radon transformation;
t2, obtaining an angle θ1 when the addition of the non-zero values after projection reaches the maximum;
t3. the horizontal tilt angle of the image should be the complement of θ1, subtracting θ1 from 90 ° to obtain the horizontal of the image
B4 comprises:
the vertical tilt algorithm using Radon transform is:
the method comprises the steps that M1, assuming that the vertical inclination range of an image is-45 degrees, carrying out projection on the image subjected to horizontal edge detection at-45 degrees by using Radon transformation;
m2, obtaining an angle theta 2 when the addition of the non-zero values after projection reaches the maximum;
m3, the vertical inclination range of the image is-45 degrees to 45 degrees, and the vertical inclination angle W of the image is obtained by subtracting 45 degrees from theta 2 3 ；
B5 comprises:
site coordinate system O 2 -X 2 Y 2 Z 2 The ideal origin isConnecting the long axis vertex with the short axis vertex to obtain two straight line foot points +.>The actual origin +.>Performing rotation and stretching distortion to obtain translational distortion parameters:
；
in the method, in the process of the invention,for corrected actual origin coordinates, +.>For rotating matrix +.>The actual origin coordinates are uncorrected.
2. The method for correcting an error in a scanning platform coordinate system based on an airborne laser radar system according to claim 1, wherein B1 comprises: calibration point as origin of coordinates O 2 The straight line along the horizontal advancing direction of the crane is Y 2 An axis passing through the origin and perpendicular to Y 2 The straight line of the axis is X 2 Shaft, formerThe straight line where the point and the rotation center of the reflecting mirror are positioned is Z 2 Shaft, build O 2 -X 2 Y 2 Z 2 A field coordinate system, a laser scanning track is in Y 2 The axis is a long axis b, and the Y positive half axis is b 1 The negative half shaft is b 2 At X 2 The axis is a short axis a, and the X positive half axis is a 1 The negative half shaft is a 2 。
3. The method for correcting an error in a scanning platform coordinate system based on an airborne laser radar system according to claim 2, wherein B2 comprises:
the long axis of the actual scanning track is measured as b ', the short axis is measured as a', and the intersection point of the long axis and the short axis is measured as the actual origin O 2 ' obtaining the origin coordinate in the site coordinate systemTwo long axis vertex coordinates->And->Two short axis vertex coordinatesAnd->。
4. The method for correcting an error in a scanning platform coordinate system based on an airborne laser radar system according to claim 1, wherein B6 comprises:
an error correction formula is carried out on an ideal scanning platform:
；
wherein,for uncorrected coordinates in the ideal scanning platform coordinate system, +.>In order to translate the correction parameters,for rotating matrix +.>The corrected ideal coordinate system coordinates;
performing precision evaluation by using the corrected ideal coordinate system coordinates, and outputting a scanning platform error calibration equation if the calibration difference is smaller than a set precision threshold; if the correction difference is larger than the set precision threshold, carrying out secondary correction on the basis of the corrected scanning platform, drawing a coordinate graph of the long and short axis coordinates and the actual long and short axis coordinates under the corrected scanning platform, and generating a plane binarization image until the correction value of the obtained coordinates and the actual coordinates is smaller than the set precision threshold under the corrected scanning platform, and meeting the precision requirement:
；
in the method, in the process of the invention,for (I)>For (I)>Is that;
during secondary correction, scanning a platform error correction equation:
；
and (3) scanning a platform error correction equation during n times of correction:
；
in the secondary correction type, the correction amount is set,for correcting the coordinates in the scanning platform coordinate system once, +.>Correction parameters for secondary translation, < >>Is a quadratic rotation matrix +.>The ideal coordinate system coordinate after the secondary correction;
in the n-time correction type, the correction is performed,correcting the coordinates of the scanning platform in the coordinate system for n-1 times,/for>Correction parameters for n translations,>for n rotation matrices +.>And the coordinates of the ideal coordinate system after n times of correction are the coordinates which finally meet the precision requirement and the error correction equation of the scanning platform.
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