cv_bridge::toCvCopy

`cv_bridge::toCvCopy`是ROS中一个非常有用的函数，它可以将ROS定义的图像消息转换为OpenCV中的Mat矩阵格式。下面是一个使用`cv_bridge::toCvCopy`函数的例子：

#include <ros/ros.h>
#include <image_transport/image_transport.h>
#include <cv_bridge/cv_bridge.h>
#include <opencv2/highgui/highgui.hpp>

void imageCallback(const sensor_msgs::ImageConstPtr& msg)
{
  try
  {
    cv::Mat img;
    img = cv_bridge::toCvCopy(msg, sensor_msgs::image_encodings::BGR8)->image;
    cv::imshow("view", img);
    cv::waitKey(30);
  }
  catch (cv_bridge::Exception& e)
  {
    ROS_ERROR("Could not convert from '%s' to 'bgr8'.", msg->encoding.c_str());
  }
}

int main(int argc, char** argv)
{
  ros::init(argc, argv, "image_listener");
  ros::NodeHandle nh;
  cv::namedWindow("view");
  cv::startWindowThread();
  image_transport::ImageTransport it(nh);
  image_transport::Subscriber sub = it.subscribe("camera/image", 1, imageCallback);
  ros::spin();
  cv::destroyWindow("view");
}

在上面的例子中，`cv_bridge::toCvCopy`函数将ROS中的图像消息转换为OpenCV中的Mat矩阵格式，并将其存储在`img`变量中。然后，我们可以使用OpenCV的函数来处理这个图像。