ROS下编写及使用一个简单的Plugin

 

主要参考来源：http://wiki.ros.org/pluginlib/Tutorials/Writing%20and%20Using%20a%20Simple%20Plugin

1.创建一个cmake空间，在该空间下创建一个包Plugin1,依赖包pluginlib roscpp .

#mkdir -p Pluginsample/src

#cd Pluginsample

#catkin_make

#source devel/setup.bash

#catkin_create_pkg Plugin1 roscpp pluginlib

2.创建插件基类和继承类

#cd ~/Pluginsample/src/plugin1/include/plugin1
(1)创建基类RegularPolygon

#vim polygon_base.h

在新建的文件中粘贴：

  #ifndef PLUGINLIB_TUTORIALS__POLYGON_BASE_H_
  #define PLUGINLIB_TUTORIALS__POLYGON_BASE_H_
 
  namespace polygon_base   // (基类空间)
  {
   class RegularPolygon   //  (基类)
   {
     public:
       virtual void initialize(double side_length) = 0;
       virtual double area() = 0;
       virtual ~RegularPolygon(){}
 
       protected:
         RegularPolygon(){}
    };
  };
 #endif

这里创建了求多边形面积的插件基类，需要被重载。

(2)创建继承类：polygon_plugins.h

#vim polygon_plugins.h

在新建的文件中粘贴：
  #ifndef PLUGINLIB_TUTORIALS__POLYGON_PLUGINS_H_
  #define PLUGINLIB_TUTORIALS__POLYGON_PLUGINS_H_
  #include <plugin1/polygon_base.h>
  #include <cmath>
   
  namespace polygon_plugins  // (实现空间)

  {
    class Triangle : public polygon_base::RegularPolygon  // (具体实现类)

    {
     public:
        Triangle(){}
  
        void initialize(double side_length)
        {
          side_length_ = side_length;
        }
  
         double area()
         {
           return 0.5 * side_length_ * getHeight();
         }
  
         double getHeight()
         {
           return sqrt((side_length_ * side_length_) - ((side_length_ / 2) * (side_length_ / 2)));
         }
  
       private:
         double side_length_;
    };
  
    class Square : public polygon_base::RegularPolygon    //(具体实现类)

    {
       public:
         Square(){}
  
         void initialize(double side_length)
        {
           side_length_ = side_length;
        }
  
         double area()
         {
           return side_length_ * side_length_;
         }
  
       private:
         double side_length_;
  
   };
};
  #endif

这里重载实现了求多边形面积的插件：三角形、正方形面积

3.注册、编译插件

(1)声明上述插件类为插件。

# cd  ~/Pluginsample/src/plugin1/src

#vim polygon_plugins.cpp

在新创建的文件中粘贴：

 #include <pluginlib/class_list_macros.h>  //插件库宏定义
 #include <plugin1/polygon_base.h>
 #include <plugin1/polygon_plugins.h>
                                          
 PLUGINLIB_EXPORT_CLASS(polygon_plugins::Triangle, polygon_base::RegularPolygon) //声明插件类
 PLUGINLIB_EXPORT_CLASS(polygon_plugins::Square, polygon_base::RegularPolygon)

(2)编译插件。

#vim ~/Pluginsample/src/plugin1/CMakeLists.txt

在文本中添加：
include_directories(
    include
    ${catkin_INCLUDE_DIRS}
  )

add_library(polygon_plugins src/polygon_plugins.cpp) //编译库

编译包：

#cd ~/Pluginsample

#catkin_make

4.将插件添加到ROS Toolchain
创建polygon_plugins.xml，添加：
<library path="lib/libpolygon_plugins">
  <class type="polygon_plugins::Triangle" base_class_type="polygon_base::RegularPolygon">
    <description>This is a triangle plugin.</description>
  </class>
  <class type="polygon_plugins::Square" base_class_type="polygon_base::RegularPolygon">
    <description>This is a square plugin.</description>
  </class>
</library>

5.对外声明plugin：
在package.xml中添加：
<export>
  <plugin1 plugin="${prefix}/polygon_plugins.xml" />
</export>
验证声明成功：
rospack plugins --attrib=plugin plugin1
显示：polygon_plugins.xml的绝对路径。

6.使用插件：新建src/polygon_loader.cpp，粘贴：
   1 #include <pluginlib/class_loader.h>
   2 #include <plugin1/polygon_base.h>
   3
   4 int main(int argc, char** argv)
   5 {
   6   pluginlib::ClassLoader<polygon_base::RegularPolygon> poly_loader("plugin1", "polygon_base::RegularPolygon");
   7
   8   try
   9   {
  10     boost::shared_ptr<polygon_base::RegularPolygon> triangle = poly_loader.createInstance("polygon_plugins::Triangle");
  11     triangle->initialize(10.0);
  12
  13     boost::shared_ptr<polygon_base::RegularPolygon> square = poly_loader.createInstance("polygon_plugins::Square");
  14     square->initialize(10.0);
  15
  16     ROS_INFO("Triangle area: %.2f", triangle->area());
  17     ROS_INFO("Square area: %.2f", square->area());
  18   }
  19   catch(pluginlib::PluginlibException& ex)
  20   {
  21     ROS_ERROR("The plugin failed to load for some reason. Error: %s", ex.what());
  22   }
  23
  24   return 0;
  25 }

7.在CMakelists.txt中添加：
add_executable(polygon_loader src/polygon_loader.cpp)
target_link_libraries(polygon_loader polygon_plugins ${catkin_LIBRARIES})

8.执行：
./~Pluginsample/devel/lib/pluginlib_tutorials_/polygon_loader
输出：
[ INFO] [WallTime: 1279658450.869089666]: Triangle area: 43.30
[ INFO] [WallTime: 1279658450.869138007]: Square area: 100.00