ROS learning_ Basics

ROS Command line tools use

One 、 Common commands

• roscore ： start-up ros
• rosrun ：rosrun [package_name] [node_name] Call node The parameters are function package name and node name
• rosnode ：rosnode list List the currently running nodes
• rqt_graph ： Visualize the currently running nodes
• rostopic ： Operate the topic
  • rostopic pub ： Post topic news
  • rostopic type ： View message types
• rosservice ： Operate the service
  • rosservice call： Publish service request
• rosparam
• rosmsg ： Get the details of the message
• rossrv

Two 、 Example ： Turtle simulation

1. start-up ROS Master：$roscore

2. Start the turtle Simulator ：$rosrun turtlesim turtlesim_node

3. Start the turtle control node ：$rosrun turtlesim turtle_teleop_key
   Be careful ： These three commands are executed on three terminals respectively .

4. function
   

3、 ... and 、 Post topic news

Release the news Keep the turtle moving .

1. First check the message type

~$ rostopic type /turtle1/cmd_vel 
geometry_msgs/Twist

~$ rosmsg show geometry_msgs/Twist
geometry_msgs/Vector3 linear
  float64 x
  float64 y
  float64 z
geometry_msgs/Vector3 angular
  float64 x
  float64 y
  float64 z

2. Write parameters

~$ rostopic pub -r 10 /turtle1/cmd_vel geometry_msgs/Twist " linear: x: 1.0 y: 0.0 z: 0.0 angular: x: 0.0 y: 0.0 z: 0.0 "

Be careful ： Parameter alignment

3. function
   

Four 、 Publish service request

Publish service request , Add a new turtle .

1. View request information

~$ rosservice info /spawn
Node: /turtlesim
URI: rosrpc://ros2go:39063
Type: turtlesim/Spawn
Args: x y theta name

2. Release request

~$ rosservice call /spawn " x: 5.0 y: 5.0 theta: 0.0 name: 'turtle2' "
name: "turtle2"

3. function
   

5、 ... and 、 The difference between topic and service

1. topic of conversation (Topic)

• Asynchronous communication mechanism between nodes
• Use Release / subscribe Model
• Topic data ： news (Message) File format .msg
  

2. service (Service)

• Synchronous communication mechanism between nodes
• Use client / The server (C/S) Model
• data ： File format .srv