1 nodelet插件编写和使用流程介绍
ROS nodelet插件和ROS中普通插件编写流程一样，因为它们都是借助plubinlib来实现插件动态加载，都必须follow pluginlib使用规则，因此编写一个nodelet插件大致流程如下：
1.1编写nodelet插件class
由于插件基类是nodelet：：NodeLet已经存在，所以不必编写啦。
MyNodeletClass.h
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#include <nodelet/nodelet.h>
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namespace example_pkg
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{
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class MyNodeletClass : public nodelet::Nodelet
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{
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public:
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virtual void onInit();
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};
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}
1.2 导出nodelet插件
MyNodeletClass.cpp
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// this should really be in the implementation (.cpp file)
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#include <pluginlib/class_list_macros.h>
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#include <example_pkg/MyNodeletClass.h>
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namespace example_pkg
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{
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void MyNodeletClass::onInit()
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{
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NODELET_DEBUG("Initializing nodelet...");
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}
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}
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// watch the capitalization carefully
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PLUGINLIB_EXPORT_CLASS(example_pkg::MyNodeletClass, nodelet::Nodelet)
1.3 接入到ROS系统使用插件
1）编写插件描述符
MyNodeletClass.xml
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<library path="lib/libMyNodeletClass">
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<class name="example_pkg/MyNodeletClass" type="example_pkg::MyNodeletClass" base_class_type="nodelet::Nodelet">
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<description>
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This is my nodelet.
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</description>
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</class>
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</library>
2）导出插件包到ROS系统package.xml
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...
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<build_depend>nodelet</build_depend>
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<run_depend>nodelet</run_depend>
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<export>
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<nodelet plugin="${prefix}/nodelet_plugins.xml" />
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</export>
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...
3）编译插件主要是CMakeLists.txt一些修改工作4）nodelet启动文件
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<launch>
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<!--node:nodelet manager launch-->
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<node pkg="nodelet" type="nodelet" name="standalone_nodelet" args="manager" output="screen"/>
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<!--node:my nodelet launch -->
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<node pkg="nodelet" type="nodelet" name="MyNodeletClass" args="load example_pkg/MyNodeletClass standalone_nodelet" output="screen">
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</node>
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</launch>
2 实例分析分析ROS已经提供的插件nodelet_tutorial_math：2.1 编写并导出插件nodelet_tutorial_math常规做法是分成2步，第一步编写插件，放到.h文件，第二步导出插件，放到.cpp文件；这里合并到.cpp一起完成如下。nodelet插件主要编写的就是函数OnInit（继承自Nodelet），做一些ROS node基本初始化。
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#include <pluginlib/class_list_macros.h>
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#include <nodelet/nodelet.h>
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#include <ros/ros.h>
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#include <std_msgs/Float64.h>
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#include <stdio.h>
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#include <math.h> //fabs
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namespace test_nodelet
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{
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class Plus : public nodelet::Nodelet
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{
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public:
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Plus()
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: value_(0)
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{}
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private:
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virtual void onInit()
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{
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ros::NodeHandle& private_nh = getPrivateNodeHandle();
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private_nh.getParam("value", value_);
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pub = private_nh.advertise<std_msgs::Float64>("out", 10);
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sub = private_nh.subscribe("in", 10, &Plus::callback, this);
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}
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void callback(const std_msgs::Float64::ConstPtr& input)
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{
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std_msgs::Float64Ptr output(new std_msgs::Float64());
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output->data = input->data + value_;
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NODELET_DEBUG("Adding %f to get %f", value_, output->data);
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pub.publish(output);
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}
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ros::Publisher pub;
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ros::Subscriber sub;
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double value_;
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};
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PLUGINLIB_DECLARE_CLASS(test_nodelet, Plus, test_nodelet::Plus, nodelet::Nodelet);
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}
2.2 插件接入到ROS系统使用
1）编写插件描述符
nodelet_math.xml
2）导出插件到ROS系统package.xml
3）编写插件启动文件plus.launch
启动后将会看到如下节点：
4）编译插件CMakeLists.txt
