Information

Instructor: Dominic Jud, Martin Wermelinger, Marco Hutter Title: Programming for Robotics - Introduction to ROS Refererences

• Lecture
• ROS Wiki
• Tutorials

I'm going to study and summarize this course. Every picture and content belong to lectures.

Date: May 18, 2020

Overview

• TF Transformation System
• rqt User Interface
• Robot models (URDF)
• Simulation descriptions (SDF)

TF Transformation System

• Tool for keeping track of coordinate frames over time

• Maintains relationship between coordinate frames in a tree structure buffered in time

• Lets the user transform points, vectors, etc. between coordinate frames at desired time

• Implemented as publichser/subsrciber model on the topics /tf and /tf_static

  Transform Tree

  • TF listeners use a buffer to listen to all broadcasted transforms
  • Query for specific transforms from the transform tree

  Tools

  • Command line
  • Print current transform tree

  rosrun tf tf_monitor

  • Print transform between two frames

  rosrun tf tf_echo source_frame target_frame

  • View Frames
  • Creates a visual graph (PDF) of the transform tree

  rosrun tf view_frames

  • RViz
  • 3D visualization of the transforms

  Transform Listener C++ API

  #include <ros/ros.h>
  #include <tf2_ros/transform_listener.h> 
  #include <geometry_msgs/TransformStamped.h>
  
  int main(int argc, char** argv) {
  		ros::init(argc, argv, "tf2_listener"); 
  		ros::NodeHandle nodeHandle;
  
  		// Create a TF listener to fill up a buffer
      tf2_ros::Buffer tfBuffer; 
  		tf2_ros::TransformListener tfListener(tfBuffer);
  
  		ros::Rate rate(10.0); 
  		while (nodeHandle.ok()) {
  		    geometry_msgs::TransformStamped transformStamped;
  		    try {
  						//To lookup transformations
  						// use ros::Time(0) to get the latest available transform
  						transformStamped = tfBuffer.lookupTransform("base", "odom", ros::Time(0));
  				} catch (tf2::TransformException &exception) {
  						ROS_WARN("%s", exception.what()); 
  						ros::Duration(1.0).sleep(); continue;
  				}
  				rate.sleep();
  		}
  		return 0;
  }
  

rqt User Interface

• User interface based on Qt
• Lots of plugins exist
• Simple to write own plugins
• Commend
• Run

rosrun rqt_gui rqt_gui rqt

### rqt_image_view

- Visualizing images
> rosrun rqt_image_view rqt_image_view

### rqt_multiplot

- Visualizing numeric values in 2D plots
> rosrun rqt_multiplot rqt_multiplot

### rqt_graph

- Visualizing the ROS computation graph
> rosrun rqt_graph rqt_graph

### rqt_console

- Displaying and filtering ROS messages
> rosrun rqt_console rqt_console

### rqt_logger_level

- Configuring the logger level of ROS nodes
> rosrun rqt_logger_level rqt_logger_level

Robot Models (URDF)

• Unified Robot Description Format