ROS2 Examples

My repository for ros2 code examples

How to use this repository

• Create your ROS2 workspace
  mkdir ~/<your_ros2_workspace_name>/src
• Change directory into src
  cd ~/<your_ros2_workspace_name>/src
• Clone this repo
  git clone git@github.com:rizkymille/ros2-examples
• Rename ros2-examples to ros2_examples (avoid confusing ros2 package system by using snake case)
  mv ros2-examples ros2_examples
• Build package in workspace
  cd ~/<your_ros2_workspace_name>
colcon build

Some style and guides

Interface package (example_infs)

• If the interface package only uses msg type, then the package name should be:
  <package_name>_msgs
• If the interface package only uses srv type, then the package name should be:
  <package_name>_srvs
• If the interface package only uses action type, then the package name should be:
  <package_name>_acts
• If the interface package contains srv and msg type, or all the three types, then the package name should be:
  <package_name>_infs

Program package (example_programs)

This package is language mixed, that's why I still use CMakeLists even there's python program.

Python

• module folder are for module or library. And scripts are for executables.
• In executables, don't forget to add shebang line #!/usr/bin/env python3. Otherwise your program can't be found
• Refrain yourself from declaring variables in class. Use self.variable = <initial_variable>

C++

Executables

• Put variable declaration above method declaration in the class (Please don't follow ros2 examples).
• Use const and & as possible in function parameters. You'll save memory. Example: void RunTest(const int& test_num)
• Contrary to headers, you can define method body directly inside the class

Headers/Libraries

• Rather than traditional .h format, use .hpp. Put that inside include/<project_name>
• In terms of header files, write the function body in .cpp file
• The define name should be <PACKAGE_NAME>_HPP_ in #ifndef, #define, and as comments in #endif. Example: #endif //_<PACKAGE_NAME>_HPP_

ROS Styles

Message Labeling

Name should be hiearchical with slash as separator of hiearchy,contains package name as the top level of hierarchy, and represents the message.

Examples:
Service name for takeoff requests
<package_name>/motion/takeoff
Topic name for vision position
<package_name>/sensor/vision
Action name for position requests
<package_name>/motion/position
Parameter name for Proportional roll constant
<package_name>/control/PID/roll/P
Message variables
auto tkf_req_msg

Best practices:

• Always use single word whenever possible
• Create documentation in README.md for every message name and types

Message Typing

• Custom data type name should be one word and reusable
• Use available data type from ROS (like std_msgs and sensor_msgs) if possible

Variable naming

Variable for construction of message operation should be go like this:
<lowest_message_hierarchy>_<message_operation>
The message_operation should contains just 3 starting syllables
Example:

• Service name for takeoff requests
  Server:
  takeoff_ser
  Client:
  takeoff_cli
• Topic name for vision position
  Publisher:
  vision_pub
  Subscriber:
  vision_sub
  Callback:
  vision_cb
• Action name for position requests
  Special case: use _act_ between message operation and lowest message hierarchy as designator
  Client:
  pos_act_cli
  Server:
  pos_act_ser
• Timer name for trajectory publishing task
  Timer naming should be representing what the task it is doing
  Example:
  publish_trajectory_timer
• Callback group
  Callback group naming is based on priority number
  Example:
  prio_1_cb_group
prio_2_cb_group