使用机器人操作系统ROS 2和仿真软件Gazebo 9命令遥控可视化教程（二）

上一篇，已经在Gazebo 9中放入了一个支持ROS 2的仿真机器人，具体参考：

使用机器人操作系统ROS 2和仿真软件Gazebo 9搭建机器人教程（一）

本篇，通过此案例学习并熟练掌握ROS2的如下内容：

ROS2常用命令回顾
遥控机器人在环境中运动
rqt和rviz2
摄像头图像显示和激光数据可视化

ROS2入门介绍参考：https://zhuanlan.zhihu.com/p/96940278

$ ros2 launch mobot world.launch.py

具体流程参考下图，配置不同会有路径和目录的差异：

节点

$ ros2 node
usage: ros2 node [-h]
Call `ros2 node <command> -h` for more detailed usage. ...

Various node related sub-commands

optional arguments:
-h, --help show this help message and exit

Commands:
info Output information about a node
list Output a list of available nodes

Call `ros2 node <command> -h` for more detailed usage.

使用其中list：

$ ros2 node list
/launch_ros
/gazebo
/mobot/camera_controller
/mobot/gazebo_ros_head_hokuyo_controller
/mobot/skid_steer_drive_controller

第一个为ros接口，第二个为gazebo，第三到五个，为Gazebo插件的控制器对应摄像头、激光测距和运动驱动。

如果需要查看更具体的节点信息，如camera：

$ ros2 node info /mobot/camera_controller
/mobot/camera_controller
Subscribers:
/clock: rosgraph_msgs/msg/Clock
/mobot/parameter_events: rcl_interfaces/msg/ParameterEvent
Publishers:
/mobot/camera/image: sensor_msgs/msg/Image
/mobot/camera/image/camera_info: sensor_msgs/msg/CameraInfo
/mobot/parameter_events: rcl_interfaces/msg/ParameterEvent
/mobot/rosout: rcl_interfaces/msg/Log
Services:
/mobot/camera_controller/describe_parameters: rcl_interfaces/srv/DescribeParameters
/mobot/camera_controller/get_parameter_types: rcl_interfaces/srv/GetParameterTypes
/mobot/camera_controller/get_parameters: rcl_interfaces/srv/GetParameters
/mobot/camera_controller/list_parameters: rcl_interfaces/srv/ListParameters
/mobot/camera_controller/set_parameters: rcl_interfaces/srv/SetParameters
/mobot/camera_controller/set_parameters_atomically: rcl_interfaces/srv/SetParametersAtomically
/mobot/set_camera_info: sensor_msgs/srv/SetCameraInfo

此处需要注意，Dashing和Eloquent信息有一些的差异哦！

如果使用是Eloquent，如下：

$ ros2 node info /mobot/camera_controller
/mobot/camera_controller
Subscribers:
/clock: rosgraph_msgs/msg/Clock
/mobot/parameter_events: rcl_interfaces/msg/ParameterEvent
Publishers:
/mobot/camera/image: sensor_msgs/msg/Image
/mobot/camera/image/camera_info: sensor_msgs/msg/CameraInfo
/mobot/parameter_events: rcl_interfaces/msg/ParameterEvent
/mobot/rosout: rcl_interfaces/msg/Log
Service Servers:
/mobot/camera_controller/describe_parameters: rcl_interfaces/srv/DescribeParameters
/mobot/camera_controller/get_parameter_types: rcl_interfaces/srv/GetParameterTypes
/mobot/camera_controller/get_parameters: rcl_interfaces/srv/GetParameters
/mobot/camera_controller/list_parameters: rcl_interfaces/srv/ListParameters
/mobot/camera_controller/set_parameters: rcl_interfaces/srv/SetParameters
/mobot/camera_controller/set_parameters_atomically: rcl_interfaces/srv/SetParametersAtomically
/mobot/set_camera_info: sensor_msgs/srv/SetCameraInfo
Service Clients:

Action Servers:

Action Clients:

如上所见，该节点正在发布、订阅和由该节点提供的服务以及该节点充当客户端的服务的所有主题都会列出。

主题

$ ros2 topic
usage: ros2 topic [-h] [--include-hidden-topics]
Call `ros2 topic <command> -h` for more detailed usage. ...

Various topic related sub-commands

optional arguments:
-h, --help show this help message and exit
--include-hidden-topics
Consider hidden topics as well

Commands:
bw Display bandwidth used by topic
delay Display delay of topic from timestamp in header
echo Output messages from a topic
find Output a list of available topics of a given type
hz Print the average publishing rate to screen
info Print information about a topic
list Output a list of available topics
pub Publish a message to a topic
type Print a topic's type

Call `ros2 topic <command> -h` for more detailed usage.

例如list：

$ ros2 topic list
/clock
/mobot/camera/image
/mobot/camera/image/camera_info
/mobot/cmd_vel
/mobot/odom
/mobot/parameter_events
/mobot/rosout
/mobot/scan
/parameter_events
/rosout
/tf

来看看图像数据和激光数据需要的带宽吧？

$ ros2 topic bw /mobot/camera/image
Subscribed to [/mobot/camera/image]
average: 27.89MB/s
   mean: 1.92MB/s min: 1.92MB/s max: 1.92MB/s window: 12
average: 28.39MB/s
   mean: 1.92MB/s min: 1.92MB/s max: 1.92MB/s window: 27
average: 25.82MB/s
   mean: 1.92MB/s min: 1.92MB/s max: 1.92MB/s window: 38
average: 26.60MB/s
   mean: 1.92MB/s min: 1.92MB/s max: 1.92MB/s window: 53

ros2 topic bw /mobot/scan
Subscribed to [/mobot/scan]
average: 169.85KB/s
   mean: 5.83KB/s min: 5.83KB/s max: 5.83KB/s window: 29
average: 163.58KB/s
   mean: 5.83KB/s min: 5.83KB/s max: 5.83KB/s window: 56
average: 163.45KB/s
   mean: 5.83KB/s min: 5.83KB/s max: 5.83KB/s window: 84
average: 164.86KB/s
   mean: 5.83KB/s min: 5.83KB/s max: 5.83KB/s window: 100

再比如：

$ ros2 topic info /mobot/cmd_vel
Type: geometry_msgs/msg/Twist
Publisher count: 0
Subscriber count: 1

如果发布消息告知机器人运动呢？

/mobot/skid_steer_drive_controller订阅/mobot/cmd_vel

目前，没有消息发布，使用teleop_twist_keyboard。

服务

此部分教程不涉及，后续补充^_^

基础知识参考：https://blog.csdn.net/zhangrelay/article/details/103493612

参数

默认节点通过修改参数可提高通用性！

Dashing：

sudo apt install ros-dashing-teleop-twist-keyboard

Eloquent：

sudo apt install ros-eloquent-teleop-twist-keyboard

命令：

$ ros2 run teleop_twist_keyboard teleop_twist_keyboard --ros-args -r __ns:=/mobot

This node takes keypresses from the keyboard and publishes them
as Twist messages. It works best with a US keyboard layout.
---------------------------
Moving around:
u i o
j k l
m , .

For Holonomic mode (strafing), hold down the shift key:
---------------------------
U I O
J K L
M < >

t : up (+z)
b : down (-z)

anything else : stop

q/z : increase/decrease max speeds by 10%
w/x : increase/decrease only linear speed by 10%
e/c : increase/decrease only angular speed by 10%

CTRL-C to quit

currently: speed 0.5 turn 1.0