大家好，我是小鱼，从公司刚到家，已经快11点了，想着今天写点其他的什么，但又觉得今天没干啥，索性把ROS2的最后两节给补齐（不怪小鱼水，实在是太忙了）
今天说说Gazebo，小鱼公司有一些同事傻傻的分不清Gazebo和Rviz之间的区别，只道是Gazebo和RVIZ都能显示机器人模型。
1.Gazebo VS Rviz2昨天小鱼有说RVIZ2是什么：
文章中讲道RVIZ2是用来可视化数据的软件，核心要义是将数据展示出来（我们不生产数据只做数据的搬运工）。 而Gazebo是用于模拟真实环境生产数据的（我们不搬运数据只做数据的生产者）
所以Gazebo可以根据我们所提供的机器人模型文件，传感器配置参数，给机器人创造一个虚拟的环境，虚拟的电机和虚拟的传感器，并通过ROS/ROS2的相关功能包把传感器数据电机数据等发送出来（生产数据）。
这样我们就不用花一分钱，就拥有了各式各样的机器人和传感器（一万八的雷达，也只不过是用鼠标拖拽一下）。
2.Gazebo集成ROS2Gazebo 是一个独立的应用程序，可以独立于 ROS 或 ROS 2 使用。
Gazebo与ROS 版本的集成是通过一组叫做gazebo_ros_pkgs的包 完成的，gazebo_ros_pkgs将Gazebo和ROS2连接起来。
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2.1 gazebo_ros_pkgs
API
ROS2通信机制
Gazebo
gazebo_ros-pkgs
ROS2
gazebo_ros_pkgs不是一个包，是一堆包如下：
- gazebo_dev：开发Gazebo插件可以用的API
- gazebo_msgs：定义的ROS2和Gazebo之间的接口（Topic/Service/Action）
- gazebo_ros：提供方便的 C++ 类和函数，可供其他插件使用，例如转换和测试实用程序。它还提供了一些通常有用的插件。gazebo_ros::Node
- gazebo_plugins：一系列 Gazebo 插件，将传感器和其他功能暴露给 ROS2 例如:
gazebo_ros_camera发布ROS2图像gazebo_ros_diff_drive通过ROS2控制和获取两轮驱动机器人的接口
ROS1的插件迁移到ROS2进度：https://github.com/ros-simulation/gazebo_ros_pkgs/wiki 
因为安装ROS2不会默认安装gazebo，所以我们要手动安装,一行命令很简单，如果提示找不到先去更新下ROS2的源。
sudo apt install gazebo11
一行代码全给装了，不差这点空间
sudo apt install ros-foxy-gazebo-*
一行代码搞定
gazebo /opt/ros/foxy/share/gazebo_plugins/worlds/gazebo_ros_diff_drive_demo.world
然后你就可以看到一个死丑死丑的小车 
通过下面的指令可看到话题和话题的类型，把目光放到这个话题/demo/cmd_demo,下面我们就通过这个话题来控制小车动起来。
ros2@ros2-TM1613R:~$ ros2 topic list -t
/clock [rosgraph_msgs/msg/Clock]
/demo/cmd_demo [geometry_msgs/msg/Twist]
/demo/odom_demo [nav_msgs/msg/Odometry]
/parameter_events [rcl_interfaces/msg/ParameterEvent]
/rosout [rcl_interfaces/msg/Log]
/tf [tf2_msgs/msg/TFMessage]
ros2 topic pub /demo/cmd_demo geometry_msgs/msg/Twist "{linear: {x: 0.2,y: 0,z: 0},angular: {x: 0,y: 0,z: 0}}"
然后就可以看到小车动了起来。
文末不说废话，把今天的文章重点总结下：
- RVIZ2是用来可视化数据的软件，核心要义是将数据展示出来（我们不生产数据只做数据的搬运工）
- Gazebo是用于模拟真实环境生产数据的（我们不搬运数据只做数据的生产者
- Gazebo是独立于ROS/ROS2的软件（还有很多仿真软件可以用ROS/ROS2）
- ROS2和Gazebo之间的桥梁是：gazebo_ros_pkgs
小鱼每天都在写文章，如果想第一时间看到小鱼，请给《鱼香ROS》一个星标吧～
