阅读说明：本技术 点云去畸变方法及车载激光雷达到imu的外参标定方法 (Point cloud distortion removal method and external reference calibration method for vehicle-mounted laser radar reaching IMU ) 是由 李帅杰 骆沛 倪凯 于 2019-09-25 设计创作，主要内容包括：本发明公开了一种点云去畸变方法及车载激光雷达到IMU的外参标定方法,其中点云去畸变方法包括如下步骤：S1、记录数据采集周期内抓取的各个点云以及所述点云的各个3D点的时间戳；S2、记录数据采集周期内IMU的运动轨迹；S3、利用所述时间戳和IMU的运动轨迹得到在采集各个所述点云时激光雷达的位置和姿态；S4、通过外参将S3得到的每帧点云的坐标值转换至该帧点云中第一个3D点采集时刻的激光雷达坐标系下,即实现了点云去畸变。其保证了车辆在运行过程中采集点云的准确度,首先在数据处理阶段提高了标定的精确度。(The invention discloses a point cloud distortion removing method and an external reference calibration method of a vehicle-mounted laser radar IMU (inertial measurement Unit), wherein the point cloud distortion removing method comprises the following steps: s1, recording each point cloud captured in a data acquisition period and the time stamp of each 3D point of the point cloud; s2, recording the motion trail of the IMU in the data acquisition period; s3, obtaining the position and the posture of the laser radar when each point cloud is collected by using the timestamp and the motion trail of the IMU; and S4, converting the coordinate value of each frame of point cloud obtained in the S3 to a laser radar coordinate system at the first 3D point acquisition time in the frame of point cloud through external reference, and then realizing point cloud distortion removal. The method ensures the accuracy of point cloud collection of the vehicle in the running process, and improves the calibration accuracy in the data processing stage.)

1. A point cloud distortion removal method comprises the following steps:

s1, recording each point cloud captured in a data acquisition period and the time stamp of each 3D point of the point cloud;

s2, recording the motion trail of the IMU in the data acquisition period;

s3, obtaining the position and the posture of the laser radar when each point cloud is collected by using the timestamp and the motion trail of the IMU;

and S4, converting the coordinate value of each frame of point cloud obtained in the S3 to a laser radar coordinate system at the first 3D point acquisition time in the frame of point cloud through external reference, and then realizing point cloud distortion removal.

2. The point cloud distortion removal method of claim 1, wherein the initial values of the external parameters are measured after the lidar is mounted to a vehicle.

3. The point cloud distortion removal method of claim 1, wherein the acquisition period is 1 frame.

4. An external reference calibration method for a vehicle-mounted laser radar IMU (inertial measurement Unit), which comprises the following steps:

step 1, collecting associated point clouds in different time periods in the point clouds obtained by the method of claim 1;

step 2, constructing a target function by utilizing the associated point clouds;

step 3, optimizing external parameters by using the objective function;

and 4, repeating the steps 1 to 3, and performing iterative optimization on the external parameters until the target function is smaller than a preset threshold value or reaches the maximum iteration times, namely calibrating the external parameters of which the vehicle-mounted laser radar reaches the IMU.

5. The extrinsic calibration method of an in-vehicle lidar IMU of claim 4, wherein the associated point clouds refer to like-name point clouds collected over different time periods.

6. The external reference calibration method of the vehicle-mounted lidar IMU of claim 5, wherein the different time periods refer to two different frames.

7. The external reference calibration method of the vehicle-mounted laser radar IMU according to claim 6, wherein the collection method of the homonymous point cloud comprises the following steps:

step 1-1, converting the point clouds of two different frames to the same coordinate system;

and 1-2, defining the point clouds with the most similar positions in two frames under the same coordinate system as the point clouds with the same name.

8. The method for extrinsic calibration of an on-board lidar IMU of claim 6, wherein the method for constructing the objective function using the associated point clouds comprises:

2-1, respectively obtaining coordinate values of the two different frames by a vehicle-mounted laser radar;

2-2, carrying out distortion removal on the coordinate values of the two different frames and unifying the coordinate values to the same coordinate system;

and 2-3, calculating the difference value between the coordinate values of the two different frames in the same coordinate system to obtain the target function.

9. The method for calibrating external parameters of an on-board lidar IMU of claim 4, wherein the external parameters are optimized by the objective function through a Gauss-Newton algorithm or an LM algorithm.

10. The external reference calibration method for the vehicle-mounted laser radar IMU according to claim 4, wherein the step 4 is followed by further comprising:

step 5, converting the associated point clouds collected in different time periods into the same coordinate system by using the external parameters for calibrating the vehicle-mounted laser radar to reach the IMU, obtained in the step 4, splicing the obtained point clouds, and judging whether the structures displayed by the spliced point clouds are clear or not; if so, calibrating the vehicle-mounted laser radar by adopting the external parameters obtained in the step 4; and if not, capturing the point cloud again.

Technical Field

The invention relates to the technical field of automatic driving, in particular to a point cloud distortion removing method and an external reference calibration method of a vehicle-mounted laser radar IMU.

Background

Autopilot, broadly refers to a technique that assists or replaces human driving of an automobile. With the development of the technology, the travel of people is more convenient, the influence of human factors of manual driving is reduced, and the driving safety can be further improved to a certain degree. Among the techniques of autopilot, high-precision positioning is important because it directly affects the inputs of other autopilot modules. Accurate positioning is a prerequisite for performing other autonomous driving functions such as sensing and decision control. The positioning of automatic driving at present mainly relies on the integration of GPS, laser radar and inertial measurement unit IMU three, and in order to guarantee the accuracy nature of vehicle location, must guarantee at first that demarcate accurate between the three, promptly guarantee vehicle-mounted laser radar to reach the accuracy of demarcating of IMU in the first place.

Disclosure of Invention

An object of the present invention is to solve at least the above problems and to provide at least the advantages described later.

It is a further object of the present invention to provide a method for point cloud distortion removal that ensures accuracy of point cloud collection during vehicle operation, and that first improves calibration accuracy during data processing.

The invention also aims to provide an external reference calibration method of the vehicle-mounted laser radar IMU, which ensures the calibration precision, improves the calibration efficiency and is easy to implement.

In order to achieve the above objects and other objects, the present invention adopts the following technical solutions:

a point cloud distortion removal method comprises the following steps:

s1, recording each point cloud captured in a data acquisition period and the time stamp of each 3D point of the point cloud;

s2, recording the motion trail of the IMU in the data acquisition period;

s3, obtaining the position and the posture of the laser radar when each point cloud is collected by using the timestamp and the motion trail of the IMU;

and S4, converting the coordinate value of each frame of point cloud obtained in the S3 to a laser radar coordinate system at the first 3D point acquisition time in the frame of point cloud through external reference, and then realizing point cloud distortion removal.

Preferably, in the point cloud distortion removal method, the initial value of the external parameter is obtained by measurement after the laser radar is installed in the vehicle.

Preferably, in the point cloud distortion removal method, the acquisition period is 1 frame.

An external reference calibration method for a vehicle-mounted laser radar IMU comprises the following steps:

step 1, collecting associated point clouds in different time periods in the point clouds obtained by the method of claim 1;

step 2, constructing a target function by utilizing the associated point clouds;

step 3, optimizing external parameters by using the objective function;

and 4, repeating the steps 1 to 3, and performing iterative optimization on the external parameters until the target function is smaller than a preset threshold value or reaches the maximum iteration times, namely calibrating the external parameters of which the vehicle-mounted laser radar reaches the IMU.

Preferably, in the external reference calibration method for the vehicle-mounted laser radar IMU, the associated point clouds refer to point clouds of the same name collected in different time periods.

Preferably, in the external reference calibration method for the vehicle-mounted laser radar IMU, the different time periods refer to two different frames.

Preferably, in the external reference calibration method for the vehicle-mounted laser radar IMU, the method for collecting the point clouds of the same name is as follows:

step 1-1, converting the point clouds of two different frames to the same coordinate system;

and 1-2, defining the point clouds with the most similar positions in two frames under the same coordinate system as the point clouds with the same name.

Preferably, in the external reference calibration method for the vehicle-mounted laser radar IMU, the method for constructing the target function by using the associated point cloud comprises the following steps:

2-1, respectively obtaining coordinate values of the two different frames by a vehicle-mounted laser radar;

2-2, carrying out distortion removal on the coordinate values of the two different frames and unifying the coordinate values to the same coordinate system;

and 2-3, calculating the difference value between the coordinate values of the two different frames in the same coordinate system to obtain the target function.

Preferably, in the external parameter calibration method for the vehicle-mounted laser radar IMU, the external parameters are optimized by using the target function through a gauss-newton algorithm or an LM algorithm.

Preferably, in the external reference calibration method for the vehicle-mounted laser radar IMU, after the step 4, the method further includes:

step 5, converting the associated point clouds collected in different time periods into the same coordinate system by using the external parameters for calibrating the vehicle-mounted laser radar to reach the IMU, obtained in the step 4, splicing the obtained point clouds, and judging whether the structures displayed by the spliced point clouds are clear or not; if so, calibrating the vehicle-mounted laser radar by adopting the external parameters obtained in the step 4; and if not, capturing the point cloud again.

The invention at least comprises the following beneficial effects:

according to the point cloud distortion removing method, the position and the posture of the laser radar are obtained when each point cloud is collected by utilizing the captured point cloud in the collection period, the timestamp of each 3D point of the point cloud and the motion track of the IMU, and then the coordinate value of each frame of point cloud is converted to the coordinate system of the laser radar at the collection moment of the first 3D point in the frame of point cloud through external parameters, so that the distortion removing of the point cloud is realized, the distortion problem of the point cloud collected in the vehicle running process is effectively removed, and the accuracy of subsequent calibration is improved in the data capturing stage.

According to the external parameter calibration method for the vehicle-mounted laser radar to the IMU, firstly, associated point clouds in different time periods are collected, then a target function is constructed by using the associated point clouds, then the external parameters are optimized by using the target function, further, the optimized external parameters are used for carrying out distortion removal on the point clouds, then the associated point clouds are used for constructing the target function, namely, iterative optimization on the external parameters is achieved, and the external parameters for calibrating the vehicle-mounted laser radar to the IMU are obtained until the target function is smaller than a preset threshold value or reaches the maximum iteration times.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Detailed Description

The present invention is described in detail below to enable one skilled in the art to practice the invention in light of the description.

A point cloud distortion removal method comprises the following steps:

s1, recording each point cloud captured in a data acquisition period and the time stamp of each 3D point of the point cloud;

s2, recording the motion trail of the IMU in the data acquisition period;

s3, obtaining the position and the posture of the laser radar when each point cloud is collected by using the timestamp and the motion trail of the IMU;

and S4, converting the coordinate value of each frame of point cloud obtained in the S3 to a laser radar coordinate system at the first 3D point acquisition time in the frame of point cloud through external reference, and then realizing point cloud distortion removal.

In the scheme, the positions and postures of the laser radar of the point clouds are obtained by utilizing the captured point clouds in the acquisition period, the timestamps of all 3D points of the point clouds and the motion tracks of the IMU, then the coordinate values of each frame of point clouds are converted to the coordinate system of the laser radar at the acquisition moment of the first 3D point in the frame of point clouds through external reference, and then distortion removal of the point clouds is realized, so that the distortion problem of the point clouds acquired in the vehicle operation process is effectively removed, and the accuracy of subsequent calibration is improved in the data processing stage.

In consideration of the characteristics of the IMU, the vehicle runs according to the 8-shaped track in the acquisition period so as to ensure that the IMU can obtain enough excitation in all directions, and further the accuracy of the acquired IMU running track is improved.

In a preferred embodiment, the initial external parameter is obtained by measurement after the lidar is mounted on a vehicle.

In a preferred embodiment, the acquisition period is 1 frame.

An external reference calibration method for a vehicle-mounted laser radar IMU comprises the following steps:

step 1, collecting associated point clouds in different time periods in the point clouds obtained by the method of claim 1;

step 2, constructing a target function by utilizing the associated point clouds;

step 3, optimizing external parameters by using the objective function;

and 4, repeating the steps 1 to 3, and performing iterative optimization on the external parameters until the target function is smaller than a preset threshold value or reaches the maximum iteration times, namely calibrating the external parameters of which the vehicle-mounted laser radar reaches the IMU.

According to the scheme, the method comprises the steps of firstly collecting associated point clouds in different time periods, then constructing a target function by using the associated point clouds, then optimizing external parameters by using the target function, and finally performing iterative optimization on the external parameters until the target function is smaller than a preset threshold value or reaches the maximum iteration number, so that the external parameters for calibrating the vehicle-mounted laser radar to reach the IMU are obtained.

In a preferred embodiment, the associated point clouds refer to point clouds of the same name collected in different time periods.

In the above scheme, the point clouds of the same name are point clouds of the same position in a scene collected at different time periods.

In a preferred embodiment, the different time periods refer to two different frames.

In a preferred embodiment, the method for collecting the point clouds with the same name comprises the following steps:

step 1-1, converting the point clouds of two different frames to the same coordinate system;

and 1-2, defining the point clouds with the most similar positions in two frames under the same coordinate system as the point clouds with the same name.

In the above scheme, when point clouds collected by point clouds of the same name in different time periods are converted into the same coordinate system, the point clouds of the same name are necessarily located at the same position theoretically, and therefore the point clouds with the most similar positions are selected as the point clouds of the same name under the condition that errors are considered.

In a preferred embodiment, the method for constructing the objective function by using the associated point clouds comprises:

2-1, respectively obtaining coordinate values of the two different frames by a vehicle-mounted laser radar;

2-2, carrying out distortion removal on the coordinate values of the two different frames and unifying the coordinate values to the same coordinate system; and the distortion removal of the coordinate value adopts the same method as the distortion removal of the point cloud.

And 2-3, calculating the difference value between the coordinate values of the two different frames in the same coordinate system to obtain the target function.

In a preferred scheme, the initial external parameters are optimized by using the target function through a Gauss Newton algorithm or an LM algorithm.

In a preferred embodiment, step 4 is followed by:

step 5, converting the associated point clouds collected in different time periods into the same coordinate system by using the external parameters for calibrating the vehicle-mounted laser radar to reach the IMU, obtained in the step 4, splicing the obtained point clouds, and judging whether the structures displayed by the spliced point clouds are clear or not; if so, calibrating the vehicle-mounted laser radar by adopting the external parameters obtained in the step 4; and if not, capturing the point cloud again.

In the scheme, whether the structure displayed by the splicing point cloud is clear or not is judged, whether the selected external parameter is accurate or not can be effectively judged, and therefore when the external parameter is inaccurate, data capture can be timely carried out again, and accurate external parameters can be obtained.

While embodiments of the invention have been disclosed above, it is not limited to the applications listed in the description and the embodiments, which are fully applicable in all kinds of fields of application of the invention, and further modifications may readily be effected by those skilled in the art, so that the invention is not limited to the specific details without departing from the general concept defined by the claims and the scope of equivalents.