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CN-122017812-A - Laser radar external parameter calibration method and system based on multi-type reference object mixing

CN122017812ACN 122017812 ACN122017812 ACN 122017812ACN-122017812-A

Abstract

The application relates to the technical field of laser detection and discloses a laser radar external parameter calibration method and system based on multi-type reference object mixing. The method comprises the steps of reading initial external parameters from a TF transformation tree, separating a single-frame laser point cloud into a calibration plate point set and a cylinder point set, respectively fitting to obtain a calibration plate normal vector, a calibration plate internal point set, a cylinder center coordinate and a cylinder internal point set, constructing residual error relative deviation by the initial external parameters on the two types of internal point sets, obtaining corrected initial values through directional pre-correction, constructing a combined residual error objective function through the corrected initial values, and obtaining the calibration external parameters through nonlinear optimization. The application improves the convergence reliability and the calibration precision of single-frame laser radar external parameter calibration under the condition that the initial external parameter has larger deviation.

Inventors

  • ZHOU WEI

Assignees

  • 天津洪荒科技有限公司

Dates

Publication Date
20260512
Application Date
20260410

Claims (10)

  1. 1. The laser radar external parameter calibration method based on the mixture of multiple types of reference objects is characterized by comprising the following steps: S1, reading initial external parameters from a TF transformation tree, and separating a single-frame laser point cloud of a laser radar carried by an AGV trolley into a calibration plate point set and a cylindrical point set according to a reference object nominal position; S2, fitting the calibration plate point set to obtain a calibration plate normal vector and a calibration plate inner point set, and fitting the cylindrical point set to obtain a cylindrical center coordinate and a cylindrical inner point set; S3, enabling the initial external parameters to act on the calibration plate inner point set and the cylinder inner point set respectively to obtain a normal residual error mean value and a radial residual error mean value, and constructing residual error relative deviation according to the difference between the normal residual error mean value and the radial residual error mean value; taking the weighted average direction of the normal vector of the calibration plate as a translation correction direction, taking the residual error relative deviation as an amplitude value to perform directional pre-correction on the translation component in the initial external parameter, performing weighted least square decomposition on the yaw angle contribution in the residual error relative deviation based on the cylindrical center coordinates to obtain a yaw angle correction, and overlapping the translation correction direction and the yaw angle correction to the initial external parameter to obtain a corrected initial value; And S4, constructing a combined residual error objective function comprising the calibration plate inner point set and the cylinder inner point set by taking the corrected initial value as a starting point, and obtaining a calibration external parameter through nonlinear optimization.
  2. 2. The method for calibrating the external parameters of the laser radar based on the mixture of the multiple types of reference objects according to claim 1, wherein the step S1 comprises: Reading a translation component and a yaw angle component of the laser radar relative to a base coordinate system from the TF transformation tree to obtain an initial external parameter; inversely transforming the nominal positions of the calibration plates and the cylinders in the base coordinate system to a laser radar coordinate system based on the initial external parameters to obtain the laser radar nominal positions of the reference objects; and (3) defining an interested region by taking the nominal position of the laser radar system of each reference object as the center, extracting points falling into the interested region of each calibration plate in a single-frame laser point cloud as a calibration plate point set, and extracting points falling into each cylindrical interested region as a cylindrical point set.
  3. 3. The method for calibrating the external parameters of the laser radar based on the mixture of the multiple types of reference objects according to claim 1, wherein the step S2 comprises: Performing RANSAC straight line fitting on the calibration plate point set, marking points with normal distances smaller than a normal distance threshold as calibration plate candidate interior points, and performing least square refinement based on the calibration plate candidate interior points to obtain calibration plate normal vectors and calibration plate interior point sets; Performing RANSAC circle fitting on the cylindrical point set under the constraint of a cylindrical nominal radius, marking points with radial distance deviation smaller than a radial distance threshold as cylindrical candidate inner points, and performing least square refinement on the basis of the cylindrical candidate inner points to obtain cylindrical center coordinates and a cylindrical inner point set; Obtaining the point rate in the calibration plate according to the point ratio of the point set in the calibration plate to the point set in the calibration plate, obtaining the point rate in the cylinder according to the point ratio of the point set in the cylinder to the point set in the cylinder, and respectively carrying out weighting marking on the point set in the calibration plate and the point set in the cylinder according to the point rate in the calibration plate and the point rate in the cylinder to obtain the point set in the calibration plate with weight and the point set in the cylinder with weight.
  4. 4. The method for calibrating the external parameters of the laser radar based on the multi-type reference object mixture according to claim 3, wherein in the step S3, the initial external parameters are applied to the calibration plate internal point set and the cylinder internal point set respectively to obtain a normal residual error mean value and a radial residual error mean value, and the method comprises the following steps: Forming a rotation translation transformation matrix by the translation component and the yaw angle component in the initial external parameters, and carrying out coordinate transformation on each point in the point set in the calibration plate based on the rotation translation transformation matrix to obtain base coordinate system coordinates of each point in the calibration plate; Calculating signed normal distances from the base coordinate system coordinates of the inner points of each calibration plate to the reference straight line based on the normal vectors of the reference straight lines corresponding to each calibration plate, and weighting and averaging the signed normal distances of the inner points of all the calibration plates according to the inner point rates of the calibration plates to obtain a normal residual error average; And carrying out coordinate transformation on each point in the cylinder inner point set based on the rotation translation transformation matrix, calculating the difference between Euclidean distance from the base coordinate system coordinates of each cylinder inner point to the corresponding reference circle center and the cylinder nominal radius, and weighting and averaging the distance deviation of all the cylinder inner points according to the cylinder inner point rate to obtain a radial residual error average value.
  5. 5. The method for calibrating a laser radar external parameter based on multi-type reference object mixing according to claim 4, wherein in the step S3, a residual error relative deviation is constructed by using a difference between the two, a weighted average direction of a normal vector of the calibration plate is taken as a translation correction direction, and a translation component in the initial external parameter is directionally pre-corrected by taking the residual error relative deviation as an amplitude, and the method comprises the following steps: The radial residual error mean value and the normal residual error mean value are subjected to difference to obtain residual error relative deviation; taking the point rate in the calibration plate of each calibration plate as a weight, and carrying out weighted average calculation on the normal vectors of the calibration plates of all the calibration plates to obtain a translation correction direction; And adding the opposite number of the product of the residual relative deviation and the horizontal axis component of the translation correction direction to the horizontal translation component of the initial external parameter, and adding the opposite number of the product of the residual relative deviation and the vertical axis component of the translation correction direction to the longitudinal translation component of the initial external parameter to obtain a translation pre-correction initial value.
  6. 6. The method for calibrating a laser radar external parameter based on multi-type reference object mixing according to claim 5, wherein in the step S3, a yaw angle correction amount is obtained by performing weighted least square decomposition on a yaw angle contribution amount in the residual error relative deviation based on the cylindrical center coordinates, and the translational correction direction and the yaw angle correction amount are added to the initial external parameter to obtain a corrected initial value, and the method comprises: Calculating geometric sensitivity coefficients of the cylinders to yaw angle errors based on Euclidean distances from the center coordinates of the cylinders to the origin of a base coordinate system, and carrying out weighted least square solution on a linear equation set formed by the residual error relative deviation and the geometric sensitivity coefficients by taking the cylinder internal point rate of each cylinder as a weight to obtain yaw angle correction values; And adding the yaw angle correction amount to the yaw angle component of the translation pre-correction initial value to obtain a corrected initial value.
  7. 7. The method for calibrating a lidar external parameter based on the mixture of multiple types of references according to claim 6, wherein the step S4 comprises: Constructing a calibration plate residual error item by taking the corrected initial value as an optimized variable starting point, carrying out rotary translation transformation on each point in the weighted calibration plate internal point set to a signed normal distance corresponding to a reference straight line, constructing a cylindrical residual error item by taking the difference between the Euclidean distance of each point in the weighted cylindrical internal point set to a corresponding reference circle center and the nominal radius of the cylinder after rotary translation transformation, taking the calibration plate internal point rate and the cylindrical internal point rate as weight coefficients of the calibration plate residual error item and the cylindrical residual error item respectively, and carrying out weighted summation on the calibration plate residual error item and the cylindrical residual error item to obtain a combined residual error target function; Applying a Huber loss function to each residual item in the combined residual objective function, reserving a secondary form for the residual item with the residual absolute value smaller than a Huber threshold, and converting the residual item with the residual absolute value not smaller than the Huber threshold into a linear form to obtain a robust combined residual objective function; taking the corrected initial value as a starting point, carrying out nonlinear iteration solution on the robust joint residual error objective function, and stopping iteration when the parameter variation of two adjacent iterations is smaller than a convergence threshold value to obtain a calibration external parameter; And comparing the optimized termination residual root mean square taking the corrected initial value as a starting point with the optimized termination residual root mean square taking the initial external parameter as a starting point, taking the calibrated external parameter as an output result when the termination residual root mean square corresponding to the corrected initial value is smaller than the termination residual root mean square corresponding to the initial external parameter, otherwise taking the re-optimized result taking the initial external parameter as the starting point as the output result.
  8. 8. A multi-type reference mixture based laser radar external reference calibration system for implementing the multi-type reference mixture based laser radar external reference calibration method according to any one of claims 1 to 7, the multi-type reference mixture based laser radar external reference calibration system comprising: The separation module is used for reading initial external parameters from the TF transformation tree, and separating a single-frame laser point cloud of the laser radar carried by the AGV trolley into a calibration plate point set and a cylindrical point set according to the nominal position of a reference object; the fitting module is used for fitting the calibration plate point set to obtain a calibration plate normal vector and a calibration plate inner point set, and fitting the cylindrical point set to obtain a cylindrical center coordinate and a cylindrical inner point set; The weighting module is used for respectively acting the initial external parameters on the calibration plate inner point set and the cylinder inner point set to obtain a normal residual error mean value and a radial residual error mean value, and constructing residual error relative deviation according to the difference between the normal residual error mean value and the radial residual error mean value; taking the weighted average direction of the normal vector of the calibration plate as a translation correction direction, taking the residual error relative deviation as an amplitude value to perform directional pre-correction on the translation component in the initial external parameter, performing weighted least square decomposition on the yaw angle contribution in the residual error relative deviation based on the cylindrical center coordinates to obtain a yaw angle correction, and overlapping the translation correction direction and the yaw angle correction to the initial external parameter to obtain a corrected initial value; and the optimization module is used for constructing a combined residual error objective function comprising the calibration plate inner point set and the cylinder inner point set by taking the corrected initial value as a starting point, and obtaining a calibration external parameter through nonlinear optimization.
  9. 9. A multi-type reference mixture based laser radar external reference calibration device, comprising a memory and a processor, the memory storing a computer program executable on the processor, the processor implementing the multi-type reference mixture based laser radar external reference calibration method of any one of claims 1 to 7 when executing the computer program.
  10. 10. A computer-readable storage medium, on which a computer program is stored, characterized in that the computer program, when being executed by a processor, causes the processor to perform the laser radar external parameter calibration method based on multi-type reference object mixing as claimed in any one of claims 1 to 7.

Description

Laser radar external parameter calibration method and system based on multi-type reference object mixing Technical Field The application relates to the technical field of laser detection, in particular to a laser radar external parameter calibration method and system based on multi-type reference object mixing. Background The laser radar external parameter calibration is a basic link for realizing accurate navigation positioning of an AGV trolley, the external parameter calibration aims at determining the translation amount and yaw angle of a laser radar coordinate system relative to an AGV trolley base coordinate system, the existing calibration method based on the target object generally arranges a single type of geometric reference object in a laser radar field of view, the external parameter is solved by extracting geometric features of the reference object and constructing a nonlinear optimization problem, the common reference object type comprises a plane calibration plate and a cylinder, the calibration plate provides linear feature constraint, the cylinder provides circular feature constraint, and the two types of reference objects respectively have constraint capacities in different directions on a translation component and a yaw angle component. However, when only a single type of reference object is used, the geometric constraint direction is single, the constraint capacity of the reference object in a certain parameter direction is weak, so that the calibration precision of the direction is lower, and in order to solve the problem of insufficient constraint of the single type of reference object, part of methods introduce multi-type reference object mixed use, but the existing multi-type reference object mixed calibration methods directly superimpose residual errors of different types of reference objects into a unified objective function, and the constraint capacity difference of the different types of reference objects in each parameter direction is not distinguished and utilized, so that the constraint complementation advantage of multi-type reference object mixed use is not fully exerted. The conventional multi-type reference object mixed calibration method directly takes a mechanical installation nominal value stored in a TF transformation tree as an initial external parameter of nonlinear optimization, the response mechanism of a normal residual error of a calibration plate and a radial residual error of a cylinder to the initial external parameter error is basically different, the normal residual error of the calibration plate mainly reflects error projection of a translation component in a normal direction, the radial residual error of the cylinder is simultaneously comprehensively influenced by the translation error and a yaw angle error, the relative deviation between the two types of residual errors naturally carries distribution information of the initial external parameter error in different parameter directions, the information is not utilized in the prior art, the initial external parameter with systematic deviation is directly taken as an optimization starting point, the nonlinear optimization starts at a position far away from the actual external parameter, the risk of converging to local optimum exists, and the reliability of a calibration result is difficult to ensure when the initial external parameter deviation is larger. Disclosure of Invention The application provides a laser radar external parameter calibration method and system based on multi-type reference object mixing, which solve the problems that the existing multi-type reference object mixing calibration method cannot utilize the relative deviation of residual errors of two types of reference objects to identify the error leading direction of an initial external parameter, so that the quality of an optimized starting point is low, and improve the convergence reliability and calibration precision of single-frame laser radar external parameter calibration under the condition that the initial external parameter has larger deviation. In a first aspect, the present application provides a method for calibrating a laser radar external parameter based on multi-type reference object mixing, where the method for calibrating the laser radar external parameter based on multi-type reference object mixing includes: S1, reading initial external parameters from a TF transformation tree, and separating a single-frame laser point cloud of a laser radar carried by an AGV trolley into a calibration plate point set and a cylindrical point set according to a reference object nominal position; S2, fitting the calibration plate point set to obtain a calibration plate normal vector and a calibration plate inner point set, and fitting the cylindrical point set to obtain a cylindrical center coordinate and a cylindrical inner point set; S3, enabling the initial external parameters to act on the calibration plate inner point set and the cylin