基于ROS利用客户端和服务端实现C++节点和python节点间传送图像

配置ROS下和python3通信以及配置python3可用的cv_bridge

• 环境安装和使用

参考：https://blog.csdn.net/qq_33445388/article/details/116034290

sudo apt-get install ros-melodic-cv-bridge python-catkin-tools python3-dev python3-catkin-pkg-modules python3-numpy python3-yaml 

在需要用到的cv_bridge工作空间内(将vision_opencv作为另一package了)

 git clone https://github.com/ros-perception/vision_opencv.git src/vision_opencv
 apt-cache show ros-melodic-cv-bridge | grep Version
 cd src/vision_opencv/
 git checkout 1.13.0
 cd ../../

指示catkin将内置包安装到安装位置，

catkin config --install
catkin build cv_bridge

需要使用cv_bridge的时候 source install/setup.bash --extend 即可自己建立的其他功能包正常catkin_make
例如， catkin_make -DCATKIN_WHITELIST_PACKAGES=service_example -DPYTHON_EXECUTABLE=/usr/bin/python3
指定编译有改动的某一package,以及和python3通信时用-DPYTHON_EXECUTABLE=/usr/bin/python3

• cv_bridge传递ROS下的图像消息在python和C++中的使用

C++
cv::Mat---->cv_bridge::CvImagePtr---->sensor_msgs::Image

  sensor_msgs::ImagePtr msgLeft;
    msgLeft = cv_bridge::CvImage(std_msgs::Header(), "rgb8",imLeft ).toImageMsg();
    srv.request.src=*msgLeft;

sensor_msgs::Image---->cv_bridge::CvImagePtr---->cv::Mat

sensor_msgs::Image msg=srv.response.dit;#request.dit是sensor_msgs::Image格式
cv_bridge::CvImagePtr cv_ptr = cv_bridge::toCvCopy(msg,  "rgb8"); 
cv::Mat imResponse= cv_ptr->image;

python
sensor_msgs::Image----->cv2能处理的格式

   cv_img = bridge.imgmsg_to_cv2(request.src, "rgb8")#request.src是sensor_msgs::Image格式
    # cv2.imshow("frame" , cv_img)
    # cv2.waitKey(1)
    im= cv2.resize(cv_img, (400, 400))

cv2能处理的格式----->sensor_msgs::Image

  response.dit=bridge.cv2_to_imgmsg(im, "rgb8")

cv_bridge编码信息
mono8: CV_8UC1, grayscale image
mono16: CV_16UC1, 16-bit grayscale image
bgr8: CV_8UC3, color image with blue-green-red color order
rgb8: CV_8UC3, color image with red-green-blue color order
bgra8: CV_8UC4, BGR color image with an alpha channel
rgba8: CV_8UC4, RGB color image with an alpha channel

2.报错解决

有未定义的引用时，一般是库没链接到位

find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
  sensor_msgs
  message_generation
  cv_bridge
  image_transport
)

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES service_example
 CATKIN_DEPENDS roscpp rospy std_msgs sensor_msgs message_runtime cv_bridge
#  DEPENDS system_lib
)
)

3.友情提醒

http://wiki.ros.org/cn/ROS/Tutorials
要用到ros的某个基础模块时，如cv_bridge，在该网址里搜索cv_bridge即可