1 硬體

攝像頭：1個;

USB資料線：1個；

1.1 準備

這裡需要使用usb-cam軟體包：

$ cd ~/catkin_ws/src  
$ git clone https://github.com/bosch-ros-pkg/usb_cam.git  
$ cd ~/catkin_ws  
$ catkin_make  

 注意：下面的程式執行前，需要啟動usb_cam節點。

roslaunch usb_cam usb_cam-test.launch

執行上面的節點，這時該節點會不斷的釋出/usb_cam/image_raw話題。

下面的程式將使用這個話題資料。

2 程式

這個程式是對上篇教程的補充。。。對比下，可以更好的分析出一些有意思的東西。

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

static const std::string OPENCV_WINDOW = "Raw Image window";
static const std::string OPENCV_WINDOW_1 = "Edge Detection";

class Edge_Detector
{
  ros::NodeHandle nh_;
  image_transport::ImageTransport it_;
  image_transport::Subscriber image_sub_;
  image_transport::Publisher image_pub_;
  
public:
  Edge_Detector()
    : it_(nh_)
  {
    // Subscribe to input video feed and publish output video feed
    image_sub_ = it_.subscribe("/usb_cam/image_raw", 1, 
      &Edge_Detector::imageCb, this);
    image_pub_ = it_.advertise("/edge_detector/raw_image", 1);
    cv::namedWindow(OPENCV_WINDOW);

  }

  ~Edge_Detector()
  {
    cv::destroyWindow(OPENCV_WINDOW);
  }

//回撥函式
  void imageCb(const sensor_msgs::ImageConstPtr& msg)
  {

    cv_bridge::CvImagePtr cv_ptr;
    namespace enc = sensor_msgs::image_encodings;

    try
    {
      cv_ptr = cv_bridge::toCvCopy(msg, sensor_msgs::image_encodings::BGR8);
    }
    catch (cv_bridge::Exception& e)
    {
      ROS_ERROR("cv_bridge exception: %s", e.what());
      return;
    }

    // Draw an example circle on the video stream
    if (cv_ptr->image.rows > 400 && cv_ptr->image.cols > 600){

	detect_edges(cv_ptr->image);
    	image_pub_.publish(cv_ptr->toImageMsg());

	}
  }
  //OpenCV的邊緣檢測程式
  void detect_edges(cv::Mat img)
  {

   	cv::Mat src, src_gray;
	cv::Mat dst, detected_edges;

	int edgeThresh = 1;
	int lowThreshold = 200;
	int highThreshold =300;
	int kernel_size = 5;

	img.copyTo(src);

	cv::cvtColor( img, src_gray, CV_BGR2GRAY );
        cv::blur( src_gray, detected_edges, cv::Size(5,5) );
	cv::Canny( detected_edges, detected_edges, lowThreshold, highThreshold, kernel_size );

  	dst = cv::Scalar::all(0);
  	img.copyTo( dst, detected_edges);
	dst.copyTo(img);

    	cv::imshow(OPENCV_WINDOW, src);
    	cv::imshow(OPENCV_WINDOW_1, dst);
    	cv::waitKey(3);

  }	
 
};

int main(int argc, char** argv)
{
  ros::init(argc, argv, "Edge_Detector");
  Edge_Detector ic;
  ros::spin();
  return 0;
}
 

 2.1 CMakeLists.txt檔案

這個很重要，以後再寫程式可以直接參考這個檔案：

如果有不懂的可以參考ROS學習筆記15（ROS/CMakeLists.txt檔案）：

cmake_minimum_required(VERSION 2.8.3)
project(cv_bridge_tutorial_pkg)

find_package(catkin REQUIRED COMPONENTS
  cv_bridge
  image_transport
  roscpp
  sensor_msgs
  std_msgs
  )

find_package( OpenCV REQUIRED )

catkin_package()

include_directories(
  ${catkin_INCLUDE_DIRS}
  ${OpenCV_INCLUDE_DIRS}
)

add_executable(sample_cv_bridge_node src/sample_cv_bridge_node.cpp)

target_link_libraries(sample_cv_bridge_node
   ${catkin_LIBRARIES}
   ${OpenCV_LIBRARIES}
 )

include_directories(${catkin_INCLUDE_DIRS} ${OpenCV_INCLUDE_DIRS})
 

2.3 package.xml檔案

不懂得也可以參考《ROS學習筆記6（package.xml》

<?xml version="1.0"?>
<package>
  <name>cv_bridge_tutorial_pkg</name>
  <version>0.0.0</version>
  <description>The cv_bridge_tutorial_pkg package</description>

  <!-- One maintainer tag required, multiple allowed, one person per tag --> 
  <!-- Example:  -->
  <!-- <maintainer email="[email protected]">Jane Doe</maintainer> -->
  <maintainer email="[email protected]">lentin</maintainer>


  <!-- One license tag required, multiple allowed, one license per tag -->
  <!-- Commonly used license strings: -->
  <!--   BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->
  <license>TODO</license>


  <!-- Url tags are optional, but mutiple are allowed, one per tag -->
  <!-- Optional attribute type can be: website, bugtracker, or repository -->
  <!-- Example: -->
  <!-- <url type="website">http://wiki.ros.org/cv_bridge_tutorial_pkg</url> -->


  <!-- Author tags are optional, mutiple are allowed, one per tag -->
  <!-- Authors do not have to be maintianers, but could be -->
  <!-- Example: -->
  <!-- <author email="[email protected]">Jane Doe</author> -->


  <!-- The *_depend tags are used to specify dependencies -->
  <!-- Dependencies can be catkin packages or system dependencies -->
  <!-- Examples: -->
  <!-- Use build_depend for packages you need at compile time: -->
  <!--   <build_depend>message_generation</build_depend> -->
  <!-- Use buildtool_depend for build tool packages: -->
  <!--   <buildtool_depend>catkin</buildtool_depend> -->
  <!-- Use run_depend for packages you need at runtime: -->
  <!--   <run_depend>message_runtime</run_depend> -->
  <!-- Use test_depend for packages you need only for testing: -->
  <!--   <test_depend>gtest</test_depend> -->
  <buildtool_depend>catkin</buildtool_depend>
  <build_depend>cv_bridge</build_depend>
  <build_depend>image_transport</build_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>sensor_msgs</build_depend>
  <build_depend>std_msgs</build_depend>
  <run_depend>cv_bridge</run_depend>
  <run_depend>image_transport</run_depend>
  <run_depend>roscpp</run_depend>
  <run_depend>sensor_msgs</run_depend>
  <run_depend>std_msgs</run_depend>


  <!-- The export tag contains other, unspecified, tags -->
  <export>
    <!-- Other tools can request additional information be placed here -->

  </export>
</package>

3 執行

首先執行：roscore

然後：roslaunch usb_cam usb_cam-test.launch

最後：rosrun cv_bridge_tutorial_pkg sample_cv_bridge_node

結果如圖所示：