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Basics

Coding Rules

The following rules apply when writing code with ROS.

.. table:: ROS Robot Programming by TurtleBot3 Developers, section 7.1.3

+------------------+--------------+---------------------------------------------+ | Type | Naming Rule | Example | +==================+==============+=============================================+ | Package | under_scored | first_ros_package | +------------------+--------------+---------------------------------------------+ | Topic, Service | under_scored | raw_image | +------------------+--------------+---------------------------------------------+ | File | under_scored | turtlebot3_fake.cpp | +------------------+--------------+---------------------------------------------+ | Namespace | under_scored | ros_awesome_package | +------------------+--------------+---------------------------------------------+ | Variable | under_scored | string table_name; | +------------------+--------------+---------------------------------------------+ | Type | camelCased | typedef int32_t PropertiesNumber; | +------------------+--------------+---------------------------------------------+ | Class | camelCased | class UrlTable | +------------------+--------------+---------------------------------------------+ | Structure | camelCased | struct UrlTableProperties | +------------------+--------------+---------------------------------------------+ | Enumeration Type | camelCased | enum ChoiceNumber | +------------------+--------------+---------------------------------------------+ | Function | camelCased | addTableEntry() | +------------------+--------------+---------------------------------------------+ | Method | camelCased | void setNumEntries(int32_t_num_entries) | +------------------+--------------+---------------------------------------------+ | Constant | ALL_CAPITALS | const uint8_t DAYS_IN_A_WEEK = T; | +------------------+--------------+---------------------------------------------+ | Marco | ALL_CAPITALS | #define PI_ROUNDED 3.0 | +------------------+--------------+---------------------------------------------+

Standard Unit in ROS

.. table:: Source : ROS Robot Programming by TurtleBot3 Developers, section 7.1.1

=========== ======== Quantity Unit =========== ======== Length Meter Mass Kilogram Time Second Current Ampere Angle Radian Frequency Hertz Force Newton Power Watt Voltage Volt Temperature Celsius =========== ========

Master

ROS master is a Server tracking all network addresses of all nodes. In addition to network addresses it also tracks other information like parameters. All nodes must know the network address of the master on startup ROS_MASTER_URI.

A master can be started with the roscore command or a roslaunch will also start a master if it doesn’t exists already.

roscore

ROS Master Publisher Slave
Figure 1: ROS Master Publisher Slave

Publisher and Subscribers

With help of the master, publisher and subscriber establish a peer-to-peer connection. All nodes must know the network address of the master on startup ROS_MASTER_URI.

ROS Publisher Slave
Figure 2: ROS Publisher Slave

  • Any node can publish a message to any topic
  • Any node can subscribe to any topic
  • Multiple nodes can publish to the same topic
  • Multiple nodes can subscribe to the same topic
  • A node can publish to multiple topics
  • A node can subscribe to multiple topics

Catkin Overview

src/ Folder

Location for creating or cloning new packages

The command catkin_make searches only in the src/ folder for packages and builds them

It is a good practice to clone the ros packages into a different folder e.g. ~/git/<package_name> and create a symlink into you catkin workspace

ls -s ~/git/<package_name>/ ~/catkin_ws/src/

build/ Folder

catkin_make create build files and intermediate cache CMake files inside the build/ folder.

devel/ Folder

catkin_make builds each package, if successful, the target executable le is created. Executables are stored inside the devel/ folder. Current workspace packages can be access by the command line if the following command is used:

# for bash
source ~/<workspace_name>/devel/setup.bash

# for zsh
source ~/<workspace_name>/devel/setup.zsh

It is beneficial to add this the the ~/.bashrc or ~/.zshrc file.

In addtion there is the catkin_tools program which simplifies the use.

See dedicated page: catkin_tools

install/ Folder

After building the executables in the devel/ folder, this executables can be install by:

catkin_make install

See also:

  • http://wiki.ros.org/catkin/workspaces#Catkin_Workspaces

Messages

  • Serialization format for structured data
  • Defined in a .msg file
  • Compiled to C++/Python classes before using them
  • more info https://wiki.ros.org/Messages ROS Message Example