CN110031824B - Laser radar combined calibration method and device - Google Patents

Laser radar combined calibration method and device Download PDF

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CN110031824B
CN110031824B CN201910294199.6A CN201910294199A CN110031824B CN 110031824 B CN110031824 B CN 110031824B CN 201910294199 A CN201910294199 A CN 201910294199A CN 110031824 B CN110031824 B CN 110031824B
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plane
point cloud
reference object
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point
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CN110031824A (en
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黄玉辉
钱炜
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Hangzhou Fabu Technology Co Ltd
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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
    • 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
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Abstract

The embodiment of the application provides a laser radar combined calibration method and device. The method comprises the steps of respectively obtaining a first point cloud obtained by scanning a reference object by a first laser radar and a second point cloud obtained by scanning the reference object by a second laser radar; determining a plane equation of a first intersecting plane of the reference object in a first coordinate system of the first laser radar based on the first point cloud, and determining coordinates of four calibration points in the first coordinate system according to the plane equation, wherein the four calibration points are not coplanar; similarly, determining the coordinates of the four calibration points in a second coordinate system of the second laser radar based on the second point cloud; and calculating to obtain a conversion matrix between the first coordinate system and the second coordinate system based on the coordinates of the four calibration points in the first coordinate system and the second coordinate system respectively, so as to perform joint calibration on the first laser radar and the second laser radar according to the conversion matrix, thereby greatly improving the calibration precision of the joint calibration of the laser radars.

Description

Laser radar combined calibration method and device
Technical Field
The application relates to the technical field of unmanned driving, in particular to a laser radar combined calibration method and device.
Background
Lidar is widely used for environmental awareness and autonomous navigation in unmanned driving.
Due to the reasons of large size of the truck, shielding of goods and the like, one laser radar cannot completely acquire 360-degree scene information of the circumference of the truck, so that a plurality of laser radars are required to be arranged at different positions of the truck for obstacle detection, and environment information is acquired. In order to fuse the environmental information acquired by a plurality of laser radars, joint calibration among the plurality of laser radars is required, that is, coordinates of the plurality of laser radars are unified into the same coordinate system.
In the prior art, point cloud registration of two laser radars is generally performed in a characteristic point-based mode, namely, registration is performed according to a target or selected characteristic points, and the method requires that point cloud depths and point cloud densities of the two laser radars have similarity, so that the method is suitable for homologous laser radars with similar wire harnesses; for the laser radars with large wire harness difference, the point cloud difference of the two laser radars is large, so that the characteristic points cannot be accurately extracted, and the calibration precision is low.
Disclosure of Invention
The application provides a laser radar combined calibration method and device, which are used for solving the technical problem that the laser radar combined calibration method in the prior art is low in calibration accuracy.
In a first aspect, an embodiment of the present invention provides a laser radar joint calibration method, including:
respectively acquiring a first point cloud obtained by scanning a reference object by a first laser radar and a second point cloud obtained by scanning the reference object by a second laser radar;
determining a plane equation of a first intersecting plane of the reference object in a first coordinate system of the first lidar based on the first point cloud, and determining a plane equation of a second intersecting plane of the reference object in a second coordinate system of the second lidar based on the second point cloud, wherein the first intersecting plane and the second intersecting plane respectively comprise three intersecting planes;
determining first coordinates of a first intersection point of the first intersecting plane in the first coordinate system based on a plane equation of the first intersecting plane in the first coordinate system, and determining second coordinates of a second intersection point of the second intersecting plane in the second coordinate system based on a plane equation of the second intersecting plane in the second coordinate system;
determining coordinates of the four calibration points in the first coordinate system and the second coordinate system based on a first coordinate of the first intersection point, a second coordinate of the second intersection point and position relations between the four calibration points on the reference object and the first intersection point and the second intersection point;
and calculating a conversion matrix between the first coordinate system and the second coordinate system based on the coordinates of the four calibration points in the first coordinate system and the second coordinate system, so as to perform joint calibration on the first laser radar and the second laser radar according to the conversion matrix.
In a second aspect, an embodiment of the present invention provides a laser radar combined calibration apparatus, including:
the point cloud acquisition module is used for respectively acquiring a first point cloud obtained by scanning a reference object by a first laser radar and a second point cloud obtained by scanning the reference object by a second laser radar;
a plane equation obtaining module, configured to determine, based on the first point cloud, a plane equation of a first intersection plane of the reference object in a first coordinate system of the first lidar, and determine, based on the second point cloud, a plane equation of a second intersection plane of the reference object in a second coordinate system of the second lidar, where the first intersection plane and the second intersection plane respectively include three intersection planes;
an intersection point coordinate obtaining module, configured to determine a first coordinate of a first intersection point of the first intersection plane in the first coordinate system based on a plane equation of the first intersection plane in the first coordinate system, and determine a second coordinate of a second intersection point of the second intersection plane in the second coordinate system based on a plane equation of the second intersection plane in the second coordinate system;
a calibration point coordinate obtaining module, configured to determine coordinates of the four calibration points in the first coordinate system and the second coordinate system based on a first coordinate of the first intersection point, a second coordinate of the second intersection point, and a position relationship between the four calibration points on the reference object and the first intersection point and the second intersection point;
and the coordinate conversion module is used for calculating a conversion matrix between the first coordinate system and the second coordinate system based on the coordinates of the four calibration points in the first coordinate system and the second coordinate system, so as to perform joint calibration on the first laser radar and the second laser radar according to the conversion matrix.
In a third aspect, an embodiment of the present invention provides a laser radar joint calibration apparatus, including a memory and a processor;
a memory: for storing the processor-executable instructions;
wherein the processor is configured to: the executable instructions are executed to implement the method of any of the first aspects.
In a fourth aspect, the present invention provides a computer-readable storage medium, in which computer-executable instructions are stored, and when executed by a processor, the computer-executable instructions are configured to implement the method according to any one of the above first aspects.
According to the laser radar combined calibration method and device provided by the embodiment of the invention, the plane equation of the first intersecting plane of the reference object is obtained to determine the first coordinate of the first intersecting point of the first intersecting plane in the first coordinate system, and the plane equation of the second intersecting plane of the reference object is obtained to determine the second coordinate of the second intersecting point of the second intersecting plane in the second coordinate system, so that compared with a method for directly extracting feature points, the coordinate accuracy of the intersecting points is high, the robustness is good, and the anti-interference performance is strong; and then according to the first coordinate of the first intersection point and the position relation between the first intersection point and the four calibration points, the coordinates of the four calibration points in a first coordinate system can be obtained, and the coordinates of the four calibration points in a second coordinate system can also be obtained.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and together with the description, serve to explain the principles of the disclosure.
Fig. 1 is a schematic structural diagram of a laser radar combined calibration system according to an embodiment of the present invention;
fig. 2 is a schematic flowchart of a laser radar joint calibration method according to an embodiment of the present invention;
fig. 3 is a schematic flowchart of a laser radar joint calibration method according to another embodiment of the present invention;
fig. 4 is a schematic flowchart of a laser radar joint calibration method according to another embodiment of the present invention;
fig. 5 is a schematic flowchart of a laser radar joint calibration method according to still another embodiment of the present invention;
fig. 6 is a schematic diagram of a calibration field of a laser radar joint calibration according to an embodiment of the present invention;
fig. 7 is a schematic flowchart of a laser radar joint calibration method according to a next embodiment of the present invention;
fig. 8 is a functional block diagram of a laser radar combined calibration apparatus according to an embodiment of the present invention;
fig. 9 is a schematic diagram of a hardware structure of a laser radar combined calibration apparatus according to an embodiment of the present invention.
With the foregoing drawings in mind, certain embodiments of the disclosure have been shown and described in more detail below. These drawings and written description are not intended to limit the scope of the disclosed concepts in any way, but rather to illustrate the concepts of the disclosure to those skilled in the art by reference to specific embodiments.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the exemplary embodiments below are not intended to represent all implementations consistent with the present disclosure. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present disclosure, as detailed in the appended claims.
Furthermore, references to the description of the terms "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" or the like, mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
With the development of science and technology and the progress of society, the unmanned technology becomes the development trend in the traffic field, when the unmanned equipment executes an automatic driving task, a laser radar arranged on the unmanned equipment is required to capture the surrounding environment, and the distance between an obstacle and unmanned assumed equipment in a link is calculated by using point cloud data of the obstacle scanned by the laser radar, so that the automatic driving strategy of the unmanned equipment is adjusted. When a plurality of laser radars are arranged at different positions of unmanned equipment (such as a truck) for obstacle detection, joint calibration among the plurality of laser radars is required to be performed so as to fuse environmental information acquired by the plurality of laser radars.
In the prior art, point cloud registration of two laser radars is generally performed in a characteristic point-based mode, namely, registration is performed according to a target or selected characteristic points, and the method requires that point cloud depths and point cloud densities of the two laser radars have similarity, so that the method is suitable for homologous laser radars with similar wire harnesses; for the laser radars with large wire harness difference, the point cloud difference of the two laser radars is large, so that the characteristic points cannot be accurately extracted, and the calibration precision is low. Therefore, a high-precision laser radar combined calibration method is required.
It should be noted that fig. 1 is a schematic diagram of an architecture of laser radar joint calibration based on the present invention, as shown in fig. 1, the laser radar joint calibration system includes an unmanned device 10, a laser radar system 20, a reference object 30, and a laser radar calibration device 40, and an execution main body of the laser radar joint calibration method provided by the present invention may specifically be the laser radar calibration device 40.
The lidar calibration device 40 may be implemented in hardware and/or software, and may specifically perform communication connection and data interaction with the lidar system 20 including a plurality of lidar 21 to receive environmental data obtained by measurement by the lidar system 20, and the lidar calibration device 40 may further perform communication connection and data interconnection with the drone device 10 to adjust an automatic driving strategy of the drone device 10.
The positions of the laser radars on the unmanned equipment 10 are fixed, and the laser radars are jointly calibrated, which is equivalent to unifying the coordinate systems of the laser radars on one coordinate system. Alternatively, in one embodiment, lidar system 20 includes two 3D lidar, a first lidar at 64 lines and a second lidar at 16 lines, with reference object 30 being located within the scanning range of both lidar. It should be understood that 16 lines and 64 lines are laser line beams emitted by the laser radar in the vertical scanning range, for example, a second laser radar of 16 lines, that is, the laser radar emits 16 laser lines in the vertical scanning range, and scans 360 degrees in the horizontal direction to acquire the surrounding environment information.
In the calibration process of laser radar calibration, coordinate systems of two laser radars are unified on one coordinate system, and the unified coordinate system can be one of the two laser radars or a third-party coordinate system. Suppose that the coordinates of a point N in the first coordinate system of the first lidar are (x)0，y0，z0) The coordinate of the point N in the second coordinate system of the second lidar is (X)0，Y0，Z0) Then, a 4 × 4 matrix T may be formed such that:
(X0，y0，Z0)T＝T*(X0，Y0，Z0) (1)
when the mutual positions of the first laser radar and the second laser radar are fixed, T is unique for any point, the joint calibration process of the first laser radar and the second laser radar is performed to solve T, and optionally, the coordinate of four calibration points on the reference object in the first coordinate system and the coordinate of the four calibration points in the second coordinate system are obtained to solve T accurately, wherein the four calibration points are not coplanar.
The following describes the technical solutions of the present application and how to solve the above technical problems with specific embodiments. The following several specific embodiments may be combined with each other, and details of the same or similar concepts or processes may not be repeated in some embodiments. Embodiments of the present application will be described below with reference to the accompanying drawings.
Fig. 2 is a schematic flow chart of a laser radar joint calibration method according to an embodiment of the present invention. As shown in fig. 2, the method includes:
s201, respectively obtaining a first point cloud obtained by scanning a reference object by a first laser radar and a second point cloud obtained by scanning the reference object by a second laser radar.
The point cloud is a three-dimensional geometrical coordinate of discrete points on the surface of an object in the field of view acquired by a laser radar, and the coordinate of each pixel point in the point cloud represents a position which accords with the actual space geometry. The method comprises the steps that a first point cloud obtained by scanning of a first laser radar needs to be converted into a first coordinate system of the first laser radar, a vertical projection point where the first laser radar is located serves as an origin coordinate of the first coordinate system, the ground height serves as a z coordinate, an x axis of the first coordinate system points to the front right when the scanning angle of the first laser radar is zero, the first coordinate system is a right-hand coordinate system, and a y axis of the first coordinate system points to the left of the first laser radar according to a right-hand rule. Optionally, the reference object is placed on the ground, and the z-axis of the first coordinate system is parallel to the height direction of the reference object.
And a second point cloud obtained by scanning the second laser radar needs to be converted into a second coordinate system of the second laser radar, a vertical projection point where the second laser radar is located is used as an origin coordinate of the second coordinate system, the ground height is used as a Z coordinate, an X axis of the second coordinate system points to the right front of the second laser radar when the scanning angle is zero, and a Y axis of the second coordinate system points to the left of the second laser radar according to a right-hand rule. Optionally, the reference object is placed on the ground, and the Z-axis of the first coordinate system is parallel to the height direction of the reference object.
Optionally, the reference object is a calibration box with known size information, and the four calibration points on the reference object are four non-coplanar corner points of the calibration box, specifically represented by A, B, C, D four points, it should be understood that, after the coordinates of any one of the four calibration points are determined, the coordinates of the other three calibration points may be calculated and solved according to the size information of the calibration box, or after the coordinates of any one corner point M of the calibration box are determined, the coordinates of the four calibration points may be obtained according to the size information of the calibration box and the positional relationship between each calibration point and the corner point M.
S202, determining a plane equation of a first intersecting plane of the reference object in a first coordinate system of the first laser radar based on the first point cloud, and determining a plane equation of a second intersecting plane of the reference object in a second coordinate system of the second laser radar based on the second point cloud, wherein the first intersecting plane and the second intersecting plane respectively comprise three intersecting planes.
Optionally, the reference object is a calibration box with known size information, the calibration box is located in a field of view of the first laser radar, a first point cloud formed by scanning the calibration box by the first laser radar includes a point cloud of a first intersecting plane and a point cloud of a calibration box placement plane, and the first intersecting plane is two adjacent side surfaces (a first side surface and a second side surface) of the calibration box and a top surface of the calibration box. Likewise, the second point cloud of the second lidar scanning calibration box comprises a point cloud of a second intersection plane, which is the two adjacent sides (third side and fourth side) of the calibration box and the top surface of the calibration box, and a point cloud of the calibration box placement plane. The first side face and the third side face or the fourth side face can be different or the same, and are determined by the placement positions of the first laser radar and the second laser radar relative to the calibration box.
In one embodiment, the first point cloud includes two adjacent side surfaces (a first side surface and a second side surface) of the calibration box, a top surface of the calibration box, and a point cloud of the calibration box placement plane, the first point cloud is intercepted and divided to obtain the point cloud of the first side surface, the point cloud of the second side surface, and the point cloud of the calibration box placement plane, respectively, and then the point clouds of the planes are subjected to plane fitting to obtain a plane equation of the first intersecting plane in the first coordinate system as follows (2):
Figure GDA0002679973040000071
it should be understood that the plane equation of the second intersection plane in the first coordinate system can be obtained by performing the intercepting and segmenting process on the second point cloud.
S203, determining a first coordinate of a first intersection point of the first intersecting plane in the first coordinate system based on a plane equation of the first intersecting plane in the first coordinate system, and determining a second coordinate of a second intersection point of the second intersecting plane in the second coordinate system based on a plane equation of the second intersecting plane in the second coordinate system.
And (3) solving the equation set in the formula (2) to obtain plane intersection points of the first side surface, the second side surface and the calibration box placing plane, namely coordinates of the first intersection points in a first coordinate system.
S204, determining coordinates of the four calibration points in the first coordinate system and the second coordinate system based on the first coordinate of the first intersection point, the second coordinate of the second intersection point and the position relation between the four calibration points on the reference object and the first intersection point and the second intersection point.
Optionally, a point a of the four calibration points is a first intersection point, and B, C, D three points are three corner points on the top surface of the calibration box, and then coordinates of the four calibration points ABCD in the first coordinate system are obtained as a (x) according to the position relationship between B, C, D and the point a, the side length of the calibration box, and the coordinates of the point a0，y0，z0)B(x1，y1，z1)C(x2，y2，z2)D(x3，y3，z3)。
Optionally, the reference object may be a triangular pyramid, a polyhedron, or the like, and after the coordinates of any one of the corner points are known, the coordinates of any one of the corner points of the reference object may be obtained according to the known side length of the reference object, and four points that are not on the same plane are selected from all the corner points as the calibration points. Alternatively, the four index points may be points on the edge of the reference object.
In order to obtain the coordinates of the four calibration points in the second coordinate system of the second lidar, optionally, based on the same processing method as for the first point cloud, a plane equation of a second intersection plane of the reference object in the second coordinate system of the second lidar is obtained, and then, based on the plane equation of the second intersection plane in the second coordinate system, the coordinates of a second intersection point of the second intersection plane in the second coordinate system are determined. And will not be described in detail herein. Optionally, the second intersection point and the first intersection point may be the same point on the reference object, or may be the same point on the part reference object, specifically determined by the relative positions of the first lidar, the second lidar and the reference object.
According to the position relation of the four index points A, B, C, D and the second intersection point and the size information of the reference object, the coordinates of the four index points A, B, C, D in the second coordinate system are calculated to be (m)0，n0，k0)(m1，n1，k1)(m2，n2，k2) And (m)3，n3，k3)。
S205, calculating a conversion matrix between the first coordinate system and the second coordinate system based on the coordinates of the four calibration points in the first coordinate system and the second coordinate system, and performing combined calibration on the first laser radar and the second laser radar according to the conversion matrix.
The rotation matrix is a transformation matrix for executing rotation transformation in European space, the transformation matrix comprises translation and rotation, the three-dimensional transformation is similar to two-dimensional transformation, the coordinates of each point in the space and the transformation of the coordinates are described by homogeneous coordinates, and the transformation matrix for describing the three-dimensional transformation of the space is in a 4 x 4 form.
From the coordinates (x) of the four index points A, B, C, D in the first coordinate system0，y0，z0)、(x1，y1，z1)、(x2，y2，z2) And (x)3，y3，z3) Coordinates (m) in a second coordinate system0，n0，k0)、(m1，n1，k1)、(m2，n2，k2) And (m)3，n3，k3) The formula for obtaining the transformation matrix is described in the following equation (3):
Figure GDA0002679973040000091
if the four calibration points are not coplanar, the coordinate matrix on the right side of the formula (3) is reversible, and T can be directly solved. In practical application, the coordinates of the points in the second coordinate system are multiplied by the transformation matrix T, i.e. the data points in the second coordinate system can be mapped into the first coordinate system, thereby completing the joint calibration of the two laser radars.
According to the laser radar combined calibration method provided by the embodiment of the invention, the plane equation of the first intersecting plane of the reference object is obtained to determine the first coordinate of the first intersecting point of the first intersecting plane in the first coordinate system, and the plane equation of the second intersecting plane of the reference object is obtained to determine the second coordinate of the second intersecting point of the second intersecting plane in the second coordinate system, so that compared with the method for directly extracting the feature points, the coordinate accuracy of the intersecting points is high, the robustness is good, and the anti-interference performance is strong; and then according to the first coordinate of the first intersection point and the position relation between the first intersection point and the four calibration points, the coordinates of the four calibration points in a first coordinate system can be obtained, and the coordinates of the four calibration points in a second coordinate system can also be obtained.
Fig. 3 is a schematic flow chart of a laser radar joint calibration method according to another embodiment of the present invention. Fig. 3 is a further optimization of step 202 based on the embodiment shown in fig. 2, wherein the first intersecting plane of the reference object includes a bottom surface of the reference object, which is attached to the placing plane, and two adjacent side surfaces of the reference object, which are connected to the bottom surface. As shown in fig. 3, the determining a plane equation of a first intersection plane of the reference object in a first coordinate system of the first lidar based on the first point cloud comprises:
s301, acquiring the point cloud of the placing plane and the point clouds of the two adjacent side faces from the first point cloud.
The point cloud is a three-dimensional geometrical coordinate of discrete points on the surface of the object in the field of view acquired by the laser radar. In one embodiment, the first point cloud is subjected to clustering processing, and a point cloud of a surface of a reference object and a point cloud of a placement plane are obtained. The surface point cloud of the reference object comprises point clouds of two adjacent side surfaces and a point cloud of a top surface of the reference object, the coordinate value of the first point cloud in the first coordinate system is known, the first point cloud is intercepted by setting a threshold range of the coordinate value, and the surface point cloud of the reference object is obtained. Optionally, a segmentation point is set, and the surface point cloud is segmented according to the coordinates of the segmentation point to obtain the point clouds on two adjacent sides of the reference object.
Optionally, before the clustering process is performed on the first point cloud, a denoising pretreatment is performed on the first point cloud to remove isolated points and scattered noise points. Optionally, the clustering method of the first point cloud includes attribute-based clustering, a region growing algorithm-based clustering method, and a model matching-based clustering algorithm.
S302, performing plane fitting processing on the point cloud of the placing plane and the point clouds of the two adjacent side faces respectively to obtain a plane equation of a first intersecting plane of the reference object in a first coordinate system of the first laser radar.
Alternatively, the plane fitting is performed based on a Random Sample Consensus (RANSAC) method.
In order to obtain a plane equation of a first intersecting plane of a reference object in a first coordinate system of the first lidar, optionally,
the method comprises the following steps: and acquiring a point cloud of a first area from the first point cloud, wherein the point cloud of the first area is composed of the point cloud of the surface of the reference object and the point cloud of the placement plane of the reference object.
Step two: and acquiring point clouds of the two adjacent sides from the point clouds on the surface of the reference object. The first step and the second step are the same as the specific implementation of S301, and are not described herein again.
Step three: and performing plane fitting processing on the point clouds of the two adjacent side surfaces to obtain a plane equation of the two adjacent side surfaces in a first coordinate system of the first laser radar. This step is the same as the specific implementation of S302, and is not described herein again.
Step four: and performing linear constraint on the point clouds in the first area by taking the plane equations of the two adjacent side surfaces as boundaries, and extracting the point clouds of the placing plane from the point clouds in the first area.
Optionally, the plane equations of the two adjacent sides are a first plane equation and a second plane equation respectively, and the point cloud of the first area is linearly constrained with the first plane equation and the second plane equation as boundaries, that is, the first plane equation and the second plane equation are both constraint conditions in a linear constraint, and specifically, the coordinates of the points in the point cloud satisfy the following formula (4):
Figure GDA0002679973040000101
when the point of the first area satisfies the above equation (4), it is explained that the point is closer to the first lidar than the points on the first side surface and the second side surface, that is, on the reference object placement plane.
Optionally, the Z axis of the first coordinate system is parallel to the height direction of the reference object, the reference object is placed on the ground, and the Z coordinate value of the placement plane of the reference object is the smallest.
Step five: and respectively carrying out plane fitting treatment on the point clouds of the placing plane to obtain a plane equation of the placing plane in a first coordinate system of the first laser radar. This step is the same as the specific implementation of S302, and is not described herein again.
According to the laser radar combined calibration method provided by the embodiment of the invention, before a plane equation of a first intersecting plane of a reference object is obtained, first point clouds are clustered to obtain a first area containing the reference object, and a data processing range is reduced from the first point cloud to the point cloud of the first area, so that the data processing range is reduced, and the processing speed is improved; then, the point clouds in the first area are intercepted, the point clouds of a reference object placing plane are removed, and the point clouds in the segmentation are all surface point clouds of the reference object, so that the plane fitting precision is improved; further, according to a plane equation of two adjacent side faces of the reference object, point clouds of the reference object placing plane are extracted, and compared with a mode of directly intercepting the point clouds of the reference object placing plane from the first point cloud, the point clouds of the reference object placing plane in the first area are obtained to the maximum extent, and then the plane fitting precision is improved.
Fig. 4 is a schematic flowchart of a laser radar joint calibration method according to another embodiment of the present invention. Fig. 4 is a further optimization of step S301 based on the embodiment shown in fig. 3, where as shown in fig. 4, the obtaining of the point clouds of the placing plane and the point clouds of the two adjacent sides from the first point cloud includes:
s401, dividing the first point cloud into a plurality of blocks according to a preset grid size.
Optionally, the preset grid size is 20cm × 20cm, the first point cloud is divided into a plurality of blocks according to the preset grid, rough division of the first point cloud is achieved, the first point cloud is rapidly divided into a plurality of smooth blocks, and each block includes a plurality of laser points.
S402, traversing the plurality of blocks to obtain the point cloud height value of each block.
The coordinates of the laser spot reflected after the laser irradiates the object are (x, y, z), the z value can be taken as the height value of the laser spot, each block comprises the coordinates of a plurality of laser spots, and the point cloud height of the block is the difference value between the maximum z coordinate value and the minimum z coordinate value of each laser spot in the block.
And S403, clustering the height of the point cloud of each block based on a region growing algorithm to obtain the point cloud with the height conforming to the height of the placement plane and the point cloud with the height conforming to the height interval of the reference object.
The point cloud height values of the blocks containing the point cloud on the surface of the reference object have similarity, and the adjacent blocks with similar characteristics are gradually grouped by adopting a region growing method, wherein the point cloud with the height conforming to the height interval of the reference object is the point cloud on the surface of the reference object, and the point cloud with the height conforming to the height of the placement plane (the height is unchanged) is the point cloud on the placement plane of the reference object.
S404, segmenting the point clouds with the heights meeting the reference object height interval to obtain the point clouds of the two adjacent side faces.
Optionally, a point closest to the first laser radar is searched from the point clouds with the heights conforming to the reference object height interval as a segmentation point, the point clouds with the heights conforming to the reference object height interval are segmented by taking the coordinates of the segmentation point as a segmentation reference to obtain a first surface point cloud and a second surface point cloud, the point with the largest Z coordinate value (the point cloud located on the top surface of the reference object) in the first surface point cloud and the second surface point cloud is respectively removed, and the point clouds of two adjacent side surfaces are obtained.
The steps of obtaining the point cloud of the placement plane from the second point cloud and the point clouds of the two adjacent side faces are the same as the method in the embodiment of fig. 4, and are not repeated here.
According to the laser radar combined calibration method provided by the embodiment of the invention, before the plane equation of the first intersecting plane of the reference object is obtained, the first point clouds are clustered to obtain the point clouds with the heights conforming to the height of the placing plane and the point clouds with the heights conforming to the height interval of the reference object, so that the data processing efficiency is improved.
Fig. 5 is a schematic flowchart of a laser radar joint calibration method according to still another embodiment of the present invention. Fig. 5 is a further optimization of step S404 based on the embodiment shown in fig. 4, where the reference object is a calibration box, and as shown in fig. 5, the obtaining of the point clouds on two adjacent sides by segmentation from the point clouds whose heights conform to the height interval of the reference object includes:
s501, intercepting and acquiring the side point cloud of the reference object from the point cloud with the height according with the height interval of the reference object. Specifically, the point cloud conforming to the height interval of the reference object is the surface point cloud of the reference object, and the surface point cloud of the reference object comprises the side point cloud of the reference object and the top point cloud of the reference object. In one embodiment, a top surface point cloud of a reference object is obtained from the point clouds of which the heights are in accordance with the height interval of the reference object according to the coordinate values of the point clouds, the top surface point cloud is removed from the point cloud of the height interval of the reference object, and a side surface point cloud of the reference object is obtained; the side point cloud of the reference object comprises a mixed point cloud of two adjacent sides.
S502, determining a first coordinate axis according to the placing position of the reference object in the first coordinate system, and selecting a point closest to the first coordinate axis in the side point cloud as a segmentation point.
And S503, dividing the side point cloud by taking the coordinates of the dividing points in the first coordinate axis direction as a dividing standard to obtain the point clouds of two adjacent sides of the reference object.
Optionally, the reference object is a calibration box with a known size, and the placement position of the calibration box in the first coordinate system is the placement direction of the calibration box relative to the first laser radar, specifically, the placement direction of two adjacent sides in the point cloud of the sides of the calibration box relative to the first laser radar.
In order to better illustrate the selection principle of the division point, in a specific embodiment, a standard calibration field is constructed, and in the standard calibration field, the arrangement position of the calibration box is fixed. Optionally, referring to fig. 6, fig. 6 is a schematic diagram (top view) of a calibration field of laser radar combined calibration according to an embodiment of the present invention; as shown in FIG. 6, the positions of the first laser radar, the second laser radar and the calibration box are fixed, and the first coordinate system of the first laser radar is X1O1Y1The second coordinate system of the second laser radar is X2O2Y2The projection point of the laser radar on the horizontal plane is the origin, and the two coordinate systems are both right-hand coordinate systems, wherein X of the first coordinate system1The axis points to the X of the second coordinate system at the right front of the first laser radar when the scanning angle is zero degree2The axis points to the X of the second coordinate system right ahead of the second laser radar when the scanning angle is zero degree1Axes and X of a second coordinate system2The axes are parallel; the Z-axes of the first and second coordinate systems are along the height direction of the calibration box, not shown in top view.
And if the position of the calibration box is fixed, the first laser radar scans a first intersecting plane of the calibration box to determine. When the calibration box is located at the first position I, two side faces in the first intersecting plane are divided by a vertical plane which passes through the point A and is parallel to the Y axis, namely the point A is a dividing point. The point A is the point closest to the X axis in the side point cloud, so the first coordinate axis is the X axis, and the point closest to the X axis in the side point cloud is selected as a segmentation point, namely the point A is the segmentation point. The X coordinate values of the point clouds on the first side face are all smaller than the X coordinate value of the point A, and the X coordinate values of the point clouds on the second side face are all larger than the X coordinate value of the point A.
And dividing the side point cloud by taking the coordinate of the dividing point in the first coordinate axis direction as a dividing reference, specifically, dividing the side point cloud by taking the X-axis coordinate value of the point A as the dividing reference, taking the point cloud of which the X-axis coordinate value is less than or equal to the dividing reference in the side point cloud as the point cloud of the first side, and taking the point cloud of which the X-axis coordinate value is greater than the dividing reference in the side point cloud as the point cloud of the second side.
Optionally, when the position of the point a is unchanged, rotating the second position ii of the calibration box value, that is, changing the placing direction of the calibration box relative to the first laser radar, and at this time, dividing two side surfaces in the first intersecting plane by a vertical plane which passes through the point C and is parallel to the X axis, that is, the point C is a dividing point, the point C is a point closest to the Y axis in the point cloud of the side surfaces, and at this time, the first coordinate axis is the Y axis; and taking the Y-axis coordinate value of the C point as a segmentation reference, segmenting the side point cloud, taking the point cloud of which the Y-axis coordinate value is less than or equal to the segmentation reference in the side point cloud as the point cloud of the first side surface, and taking the point cloud of which the Y-axis coordinate value is greater than the segmentation reference in the side point cloud as the point cloud of the second side surface.
In practical application, the point clouds on two side surfaces in the side surface point clouds are divided relative to the value of the intersection line of the two side surfaces on a first coordinate axis, when the placing direction of the calibration box relative to the first laser radar is determined, the intersection line of the two side surfaces is determined, and then the first coordinate axis is also determined.
Optionally, when the calibration box is located at the first position i, the second laser radar scans a second intersecting plane of the calibration box, two adjacent side surfaces in the second intersecting plane are divided by a point B and a vertical plane parallel to the X axis, that is, the point B is a dividing point, and the first coordinate axis of the calibration box relative to the second coordinate system is the Y axis. The process of obtaining the point clouds on two adjacent sides (the third side and the fourth side) of the calibration box in the second point cloud is the same as the method in the embodiments of fig. 4 and 5, and is not repeated here.
According to the laser radar combined calibration method provided by the embodiment, the side point cloud of the reference object is obtained by intercepting from the point cloud with the height conforming to the height interval of the reference object, the first coordinate axis is determined according to the placing position of the reference object in the first coordinate system, the point closest to the first coordinate axis is selected from the side point cloud as the dividing point, the coordinate of the dividing point in the direction of the first coordinate axis is taken as the dividing reference, the side point cloud is divided, and the point clouds of two adjacent sides of the reference object are obtained.
Fig. 7 is a schematic flowchart of a laser radar joint calibration method according to a next embodiment of the present invention. Fig. 7 is a further optimization of step S501 based on the embodiment shown in fig. 5, for example, based on the embodiment shown in fig. 5, where as shown in fig. 7, the step of extracting a side point cloud of the reference object from the point cloud whose height corresponds to the height interval of the reference object includes:
s701, selecting a maximum coordinate value and a minimum coordinate value of a height coordinate from the point cloud with the height conforming to the height interval of the reference object.
Optionally, a Z axis of the first coordinate system is parallel to a height direction of the reference object, and a height coordinate is a Z axis coordinate value of the point cloud of the height section of the reference object.
S702, selecting a target range between the maximum coordinate value and the minimum coordinate value.
In practical application, the first preset value is subtracted from the maximum coordinate value of the Z coordinate, and the second preset value is added to the minimum coordinate value of the Z coordinate to obtain the target range of the Z coordinate.
And S703, intercepting the point cloud with the height coordinate in the target range from the point cloud with the height conforming to the height interval of the reference object as the side point cloud of the reference object.
The target range of the Z coordinate is located between the maximum coordinate values and the minimum coordinate values, and since the Z coordinate value of the point cloud of the top surface of the reference object is the maximum and the Z coordinate value of the point cloud of the placement plane of the reference object is the minimum, the laser point of which the Z coordinate value is located in the target range is necessarily located on the side surface of the reference object.
Optionally, the process of obtaining the side point cloud of the reference object in the second point cloud is the same as the method in the embodiment of fig. 8, and details are not repeated here.
Based on the laser radar combined calibration method provided by the embodiment, the embodiment of the invention further provides an embodiment of a device for realizing the embodiment of the method.
Fig. 8 is a schematic structural diagram of a laser radar combined calibration apparatus according to an embodiment of the present invention. As shown in fig. 8, the laser radar combined calibration apparatus includes a point cloud obtaining module 810, a plane equation obtaining module 820, a plane equation obtaining module 830, a calibration point coordinate obtaining module 840, and a coordinate converting module 850.
The point cloud obtaining module 810 is configured to obtain a first point cloud obtained by scanning a reference object with a first laser radar and a second point cloud obtained by scanning the reference object with a second laser radar, respectively.
A plane equation obtaining module 820, configured to determine a plane equation of a first intersection plane of the reference object in a first coordinate system of the first lidar based on the first point cloud, and determine a plane equation of a second intersection plane of the reference object in a second coordinate system of the second lidar based on the second point cloud, where the first intersection plane and the second intersection plane respectively include three intersection planes.
A plane equation obtaining module 830, configured to determine a first coordinate of the first intersection point of the first intersecting plane in the first coordinate system based on a plane equation of the first intersecting plane in the first coordinate system, and determine a second coordinate of the second intersection point of the second intersecting plane in the second coordinate system based on a plane equation of the second intersecting plane in the second coordinate system.
A calibration point coordinate obtaining module 840, configured to determine coordinates of the four calibration points in the first coordinate system and the second coordinate system based on a first coordinate of the first intersection point, a second coordinate of the second intersection point, and a position relationship between the four calibration points on the reference object and the first intersection point and the second intersection point.
And a coordinate conversion module 850, configured to calculate a conversion matrix between the first coordinate system and the second coordinate system based on the coordinates of the four calibration points in the first coordinate system and the second coordinate system, so as to perform joint calibration on the first laser radar and the second laser radar according to the conversion matrix.
According to the laser radar combined calibration method provided by the embodiment of the invention, the plane equation of the first intersecting plane of the reference object is obtained to determine the first coordinate of the first intersecting point of the first intersecting plane in the first coordinate system, and the plane equation of the second intersecting plane of the reference object is obtained to determine the second coordinate of the second intersecting point of the second intersecting plane in the second coordinate system, so that compared with the method for directly extracting the feature points, the coordinate accuracy of the intersecting points is high, the robustness is good, and the anti-interference performance is strong; and then according to the first coordinate of the first intersection point and the position relation between the first intersection point and the four calibration points, the coordinates of the four calibration points in a first coordinate system can be obtained, and the coordinates of the four calibration points in a second coordinate system can also be obtained.
Optionally, the plane equation obtaining module 820 is further specifically configured to obtain the point cloud of the placement plane and the point clouds of the two adjacent sides from the first point cloud; and respectively carrying out plane fitting processing on the point cloud of the placing plane and the point clouds of the two adjacent side surfaces to obtain a plane equation of a first intersecting plane of the reference object in a first coordinate system of the first laser radar.
Optionally, the plane equation obtaining module 820 is further specifically configured to divide the first point cloud into a plurality of blocks according to a preset grid size; traversing the plurality of blocks to obtain the point cloud height value of each block; clustering the height of the point cloud of each block based on a region growing algorithm to obtain the point cloud with the height conforming to the height of the placing plane and the point cloud with the height conforming to the height interval of the reference object; and segmenting the point clouds of the two adjacent side surfaces from the point clouds of which the heights are in accordance with the height interval of the reference object.
Optionally, the plane equation obtaining module 820 is further specifically configured to intercept and obtain a side point cloud of the reference object from the point cloud whose height conforms to the height interval of the reference object; determining a first coordinate axis according to the placing position of the reference object in the first coordinate system, and selecting a point closest to the first coordinate axis in the side point cloud as a segmentation point; and dividing the side point cloud by taking the coordinates of the dividing points in the first coordinate axis direction as a dividing standard to obtain the point clouds of two adjacent sides of the reference object.
Optionally, the plane equation obtaining module 820 is further specifically configured to select a maximum coordinate value and a minimum coordinate value of the height coordinate from the point cloud whose height corresponds to the height interval of the reference object; selecting a target range between the maximum coordinate value and the minimum coordinate value; and intercepting the point cloud with the height coordinate in the target range from the point cloud with the height conforming to the height interval of the reference object as the side point cloud of the reference object.
Optionally, the plane equation obtaining module 820 is further specifically configured to obtain point clouds of the two adjacent side surfaces from the first point cloud; performing plane fitting processing on the point clouds of the two adjacent side surfaces to obtain a plane equation of the two adjacent side surfaces in a first coordinate system of the first laser radar; taking the plane equations of the two adjacent side surfaces as boundaries, performing linear constraint on the point clouds in the first area, and extracting the point clouds of the placing plane from the point clouds in the first area; and respectively carrying out plane fitting treatment on the point clouds of the placing plane to obtain a plane equation of the placing plane in a first coordinate system of the first laser radar.
The laser radar combined calibration apparatus in the embodiment shown in fig. 8 may be used to implement the technical solution in the above method embodiment, and the implementation principle and technical effect are similar, which are not described herein again.
It should be understood that the division of the modules of the laser radar combined calibration apparatus shown in fig. 8 is merely a division of logical functions, and may be wholly or partially integrated into a physical entity or physically separated in actual implementation. And these modules can be realized in the form of software called by processing element; or may be implemented entirely in hardware; and part of the modules can be realized in the form of calling by the processing element in software, and part of the modules can be realized in the form of hardware. In addition, all or part of the modules can be integrated together or can be independently realized. The processing element described herein may be an integrated circuit having signal processing capabilities. In implementation, each step of the above method or each module above may be implemented by an integrated logic circuit of hardware in a processor element or an instruction in the form of software.
Fig. 9 is a schematic diagram of a hardware structure of a laser radar combined calibration apparatus according to an embodiment of the present invention. As shown in fig. 9, the laser radar combined calibration apparatus 900 provided in this embodiment includes: at least one memory 910, a processor 920, and computer programs; stored in memory 910 and configured to be executed by processor 920 to implement a lidar joint calibration method, for example. The lidar joint calibration apparatus 900 further comprises a communication component, through which the lidar joint calibration apparatus 900 communicates with a lidar, wherein the processor 910, the memory 920 and the communication component are connected through a bus.
It will be understood by those skilled in the art that fig. 9 is merely an example of a lidar joint calibration apparatus and does not constitute a limitation of the lidar joint calibration apparatus, and that the lidar joint calibration apparatus may include more or less components than those shown, or may combine some components, or different components, for example, the lidar joint calibration apparatus may further include an input-output device, a network access device, a bus, etc.
Furthermore, an embodiment of the present invention provides a readable storage medium, on which a computer program is stored, where the computer program is executed by a processor to implement the method according to any one of the above-mentioned implementation manners.
The readable storage medium may be implemented by any type or combination of volatile or non-volatile memory devices, such as Static Random Access Memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic or optical disks. Readable storage media can be any available media that can be accessed by a general purpose or special purpose computer.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and 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 still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A laser radar combined calibration method is characterized by comprising the following steps:
respectively acquiring a first point cloud obtained by scanning a reference object by a first laser radar and a second point cloud obtained by scanning the reference object by a second laser radar;
determining a plane equation of a first intersecting plane of the reference object in a first coordinate system of the first lidar based on the first point cloud, and determining a plane equation of a second intersecting plane of the reference object in a second coordinate system of the second lidar based on the second point cloud, wherein the first intersecting plane and the second intersecting plane respectively comprise three intersecting planes;
determining first coordinates of a first intersection point of the first intersecting plane in the first coordinate system based on a plane equation of the first intersecting plane in the first coordinate system, and determining second coordinates of a second intersection point of the second intersecting plane in the second coordinate system based on a plane equation of the second intersecting plane in the second coordinate system;
determining coordinates of the four calibration points in the first coordinate system and the second coordinate system based on a first coordinate of the first intersection point, a second coordinate of the second intersection point and position relations between the four calibration points on the reference object and the first intersection point and the second intersection point;
and calculating a conversion matrix between the first coordinate system and the second coordinate system based on the coordinates of the four calibration points in the first coordinate system and the second coordinate system, so as to perform joint calibration on the first laser radar and the second laser radar according to the conversion matrix.
2. The method of claim 1, wherein the first intersecting plane of the reference object comprises a bottom surface of the reference object abutting the placement plane, and two adjacent side surfaces bordering the bottom surface;
the determining, based on the first point cloud, a plane equation of a first intersection plane of the reference object in a first coordinate system of the first lidar comprises:
acquiring the point cloud of the placing plane and the point clouds of the two adjacent side surfaces from the first point cloud;
and respectively carrying out plane fitting processing on the point cloud of the placing plane and the point clouds of the two adjacent side surfaces to obtain a plane equation of a first intersecting plane of the reference object in a first coordinate system of the first laser radar.
3. The method of claim 2, wherein the obtaining the point cloud of the placement plane and the point clouds of the two adjacent sides from the first point cloud comprises:
dividing the first point cloud into a plurality of blocks according to a preset grid size;
traversing the plurality of blocks to obtain the point cloud height value of each block;
clustering the height of the point cloud of each block based on a region growing algorithm to obtain the point cloud with the height conforming to the height of the placing plane and the point cloud with the height conforming to the height interval of the reference object;
and segmenting the point clouds of the two adjacent side surfaces from the point clouds of which the heights are in accordance with the height interval of the reference object.
4. The method of claim 3, wherein the reference object is a calibration box, and the segmenting from the point clouds whose heights are in accordance with the height interval of the reference object to obtain the point clouds of the two adjacent sides comprises:
intercepting and acquiring a side point cloud of the reference object from the point cloud with the height conforming to the height interval of the reference object;
determining a first coordinate axis according to the placing position of the reference object in the first coordinate system, and selecting a point closest to the first coordinate axis in the side point cloud as a segmentation point;
and dividing the side point cloud by taking the coordinates of the dividing points in the first coordinate axis direction as a dividing standard to obtain the point clouds of two adjacent sides of the reference object.
5. The method of claim 4, wherein the intercepting the side point cloud of the reference object from the point cloud with the height corresponding to the height interval of the reference object comprises:
selecting a maximum coordinate value and a minimum coordinate value of a height coordinate from the point cloud with the height conforming to the height interval of the reference object;
selecting a target range between the maximum coordinate value and the minimum coordinate value;
and intercepting the point cloud with the height coordinate in the target range from the point cloud with the height conforming to the height interval of the reference object as the side point cloud of the reference object.
6. The method of claim 1, wherein the first intersecting plane of the reference object comprises a bottom surface of the reference object abutting the placement plane, and two adjacent side surfaces bordering the bottom surface;
the determining, based on the first point cloud, a plane equation of a first intersection plane of the reference object in a first coordinate system of the first lidar comprises:
acquiring a point cloud of a first area from the first point cloud, wherein the point cloud of the first area is composed of a surface point cloud of the reference object and a point cloud of the reference object placement plane;
acquiring point clouds of the two adjacent side surfaces from the point clouds on the surface of the reference object;
performing plane fitting processing on the point clouds of the two adjacent side surfaces to obtain a plane equation of the two adjacent side surfaces in a first coordinate system of the first laser radar;
taking the plane equations of the two adjacent side surfaces as boundaries, performing linear constraint on the first point cloud, and extracting the point cloud of the placement plane from the first point cloud;
and respectively carrying out plane fitting treatment on the point clouds of the placing plane to obtain a plane equation of the placing plane in a first coordinate system of the first laser radar.
7. The method of claim 1, wherein the reference object is a calibration box with known dimensional information, and the four calibration points are four non-coplanar corner points of the calibration box.
8. A laser radar combined calibration device is characterized by comprising
The point cloud acquisition module is used for respectively acquiring a first point cloud obtained by scanning a reference object by a first laser radar and a second point cloud obtained by scanning the reference object by a second laser radar;
a plane equation obtaining module, configured to determine, based on the first point cloud, a plane equation of a first intersection plane of the reference object in a first coordinate system of the first lidar, and determine, based on the second point cloud, a plane equation of a second intersection plane of the reference object in a second coordinate system of the second lidar, where the first intersection plane and the second intersection plane respectively include three intersection planes;
an intersection coordinate obtaining module, configured to determine a first coordinate of a first intersection of the first intersecting plane in the first coordinate system based on a plane equation of the first intersecting plane in the first coordinate system, and determine a second coordinate of a second intersection of the second intersecting plane in the second coordinate system based on a plane equation of the second intersecting plane in the second coordinate system;
a calibration point coordinate obtaining module, configured to determine coordinates of the four calibration points in the first coordinate system and the second coordinate system based on a first coordinate of the first intersection point, a second coordinate of the second intersection point, and a position relationship between the four calibration points on the reference object and the first intersection point and the second intersection point;
and the coordinate conversion module is used for calculating a conversion matrix between the first coordinate system and the second coordinate system based on the coordinates of the four calibration points in the first coordinate system and the second coordinate system, so as to perform joint calibration on the first laser radar and the second laser radar according to the conversion matrix.
9. The laser radar combined calibration equipment is characterized by comprising a memory and a processor;
a memory: for storing the processor-executable instructions;
wherein the processor is configured to: executing the executable instructions to implement the method of any of claims 1 to 7.
10. A computer-readable storage medium having computer-executable instructions stored thereon, which when executed by a processor, are configured to implement the method of any one of claims 1 to 7.
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