相机和雷达外参联合标定

内容: 关于雷达和相机外参联合标定的踩坑纪录。

Date: 2023/03/19

硬件:

上位机: Jetson ORIN (Ubuntu 20.04, ROS noetic)
雷达: Ouster 32线
相机: Intel D435

一、标定方案

目前流行的雷达+相机标定方案有五种：Autoware, apollo, lidar_camera_calibration, but_velodyne。

Ubuntu20.04安装autoware我看bug比较多，因此我follow的是: https://github.com/ankitdhall/lidar_camera_calibration

1.1 opencv

这一步花了我一天时间，坑比较多，需要安装opencv_contrib才能进行进一步的操作,仅仅安装opencv是不行的!

我安的版本是3.4.10。

参考:

https://blog.csdn.net/m0_73694897/article/details/129175515?spm=1001.2014.3001.5506
https://blog.csdn.net/weixin_34910922/article/details/125248118?spm=1001.2014.3001.5506

二、时间强行同步

直接实时或者直接播包的话就会发生: 只有mono8这一个窗口，没有其他窗口弹出!

Only Mono8 window visible · Issue #94 · ankitdhall/lidar_camera_calibration
https://github.com/ankitdhall/lidar_camera_calibration/issues/65
https://github.com/ankitdhall/lidar_camera_calibration/issues/53

因为车是静止的，如果时间戳不完全一致，标定的程序是无法弹出点云窗口的，这个bug困扰了我很久，在issues中也没找到也没有人能给出解决方案，于是我把时间戳都强行设置到1970年，解决。

#!/usr/bin/env python3import rospy
import rosbag
import sysif sys.getdefaultencoding() != 'utf-8':reload(sys)sys.setdefaultencoding('utf-8')
bag_name = 'subset_2023-03-19-15-52-03.bag' #被修改的bag名
out_bag_name = 'change.bag' #修改后的bag名
dst_dir = '/aigo/' #使用路径with rosbag.Bag(dst_dir+out_bag_name, 'w') as outbag:stamp = None#topic:就是发布的topic msg:该topic在当前时间点下的message t:消息记录时间(非header)##read_messages内可以指定的某个topicfor topic, msg, t in rosbag.Bag(dst_dir+bag_name).read_messages():if topic == '/ouster/points':stamp = msg.header.stamp# print("imu")#print(stamp)outbag.write(topic, msg, stamp)#针对没有header的文件，使用上面帧数最高的topic(即:/gps)的时间戳##因为read_messages是逐时间读取，所以该方法可以使用elif topic == '/camera/color/image_raw' and stamp is not None: #print("lidar")#print(msg.header.stamp)outbag.write(topic, msg, stamp)#    continue# #针对格式为Header的topicelif topic == '/camera/depth/image_rect_raw' and stamp is not None:#print("image")#print(msg.header.stamp)outbag.write(topic, msg, stamp)#     outbag.write(topic, msg, msg.stamp)#     continue# #针对一般topic#outbag.write(topic, msg, msg.header.stamp)print("finished")

前:

后:

三、标定

我用的雷达是32线的，我修改了/home/nvidia/wuke/a2b_ws/src/lidar_camera_calibration/include/lidar_camera_calibration/PreprocessUtils.h:

// line 200
// std::vector <std::vector<myPointXYZRID *>> rings(16);
std::vector <std::vector<myPointXYZRID *>> rings(32);

播包:

roscorecd /aigo/
rosbag play -l --clock change.bag

标定:

cd ~/wuke/a2b_ws
source devel/setup.bashroslaunch lidar_camera_calibration find_transform.launch

四、标定结果

--------------------------------------------------------------------
After 40 iterations
--------------------------------------------------------------------
Average translation is:
0.00659326-0.241034-0.113246
Average rotation is:0.901867 0.00575031   0.431975
-0.0142371   0.999764  0.0164154-0.431778 -0.0209546   0.901736
Average transformation is: 0.901867 0.00575031   0.431975 0.00659326
-0.0142371   0.999764  0.0164154  -0.241034-0.431778 -0.0209546   0.901736  -0.1132460          0          0          1
Final rotation is:0.0174841   -0.999826 -0.006546440.0208512  0.00691063   -0.9997590.99963   0.0173434   0.0209684
Final ypr is:
0.873007
-1.543580.69106
Average RMSE is: 0.0291125
RMSE on average transformation is: 0.0298826

4.1 将雷达点云投影到相机坐标系

上面的位姿变换是从雷达坐标系到相机坐标系的变换。

我打算把雷达点云变换到相机坐标系下然后和深度图对比，看重叠效果咋样:

将D435的深度图变成点云:

#include <ros/ros.h>
#include <cv_bridge/cv_bridge.h>
#include <sensor_msgs/Image.h>
#include <sensor_msgs/CameraInfo.h>
#include <sensor_msgs/PointCloud2.h>
#include <pcl_conversions/pcl_conversions.h>
#include <pcl/point_types.h>
#include <pcl/PCLPointCloud2.h>
#include <pcl/conversions.h>
#include <iostream>
using namespace std;ros::Publisher pub_point_cloud2;bool is_K_empty = 1;
double K[9];
//     [fx  0 cx]
// K = [ 0 fy cy]
//     [ 0  0  1]void img_callback(const sensor_msgs::ImageConstPtr &img_msg)
{// Step1: 读取深度图//ROS_INFO("image format: %s %dx%d", img_msg->encoding.c_str(), img_msg->height, img_msg->width);int height = img_msg->height;int width = img_msg->width;// 通过指针强制转换，读取为16UC1数据，单位是mmunsigned short *depth_data = (unsigned short*)&img_msg->data[0];// Step2: 深度图转点云sensor_msgs::PointCloud2 point_cloud2;pcl::PointCloud<pcl::PointXYZ>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZ>);for(int uy=0; uy<height; uy++){for(int ux=0; ux<width; ux++){float x, y, z;z = *(depth_data + uy*width + ux) / 1000.0;if(z!=0){x = z * (ux - K[2]) / K[0];y = z * (uy - K[5]) / K[4];pcl::PointXYZ p(x, y, z);cloud->push_back(p);}}}// Step3: 发布点云pcl::toROSMsg(*cloud, point_cloud2);point_cloud2.header.frame_id = "world";pub_point_cloud2.publish(point_cloud2);
}void camera_info_callback(const sensor_msgs::CameraInfoConstPtr &camera_info_msg)
{// 读取相机参数if(is_K_empty){for(int i=0; i<9; i++){K[i] = camera_info_msg->K[i];}is_K_empty = 0;}
}int main(int argc, char **argv)
{ros::init(argc, argv, "ros_tutorial_node");ros::NodeHandle n;// 订阅D435i的深度图，在其回调函数中把深度图转化为点云，并发布出来ros::Subscriber sub_img = n.subscribe("/camera/depth/image_rect_raw", 100, img_callback);// 订阅D435i的深度相机参数ros::Subscriber sub_cmara_info = n.subscribe("/camera/depth/camera_info", 1, camera_info_callback);pub_point_cloud2 = n.advertise<sensor_msgs::PointCloud2>("/d435i_point_cloud", 1000);ROS_INFO("Runing ...");ros::spin();return 0;
}

发布tf变换消息:

rosrun tf2_ros static_transform_publisher 0 0 0 1.57 -1.57 0 world os_sensor

result:
- raw
- after (红色是雷达点云，白色是深度相机的投影)

Reference

[1] https://github.com/ankitdhall/lidar_camera_calibration/wiki/Welcome-to-%60lidar_camera_calibration%60-Wiki!

[2] 3D雷达与相机的标定方法详细教程_lidar_camera_calibration_敢敢のwings的博客-CSDN博客

[3] https://blog.csdn.net/m0_73694897/article/details/129175515?spm=1001.2014.3001.5506

[4] https://blog.csdn.net/weixin_34910922/article/details/125248118?spm=1001.2014.3001.5506

[5] https://blog.csdn.net/weixin_42840360/article/details/119844648?spm=1001.2014.3001.5506

[6] https://blog.csdn.net/Jeff_zjf/article/details/124255916?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522167922032616800213053412%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fall.%2522%257D&request_id=167922032616800213053412&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2_allfirst_rank_ecpm_v1~pc_rank_34-1-124255916-null-null.142