Packages

Package Structure

ROS software is organized into packages, which can contain source code, launch files, configuration files, message definitions, data, and documentation. A package can depend on other packages called dependencies.

   catkin_create_pkg <package_name> {dependencies}

A package need two things, its source code and the message definition. It is encouraging to place message definition into a separate folder.

• :fa:folder package_name

• ​:fa:folder config - parameter files (YAML)

• :fa:folder include/package_name - C++ include headers
• :fa:folder launch - *.launch files
• :fa:folder src - Source files
• :fa:folder test - Unit and or ROS Tests
• :fa:file CMakeList.txt - CMake build file

• :fa:file package.xml - Package information

• :fa:folder package_name_msgs

• :fa:folder action - Action definitions

• :fa:folder msg - Message definitions
• :fa:folder src - Service definitions
• :fa:file CMakeList.txt - CMake build file
• :fa:file package.xml - Package information

More info

• http://wiki.ros.org/Packages

Package Files

:fa:file package.xml

• The package.xml file defines the properties of the package

• Package name

• Version number
• Authors
• Dependencies on other packages
• ...

<?xml version="1.0"?>
<package format="2">
      <name>ros_package_template</name>
      <version>0.1.0</version>
      <description>A template for ROS packages.</description>
      <maintainer email="user@email.ch">Firstname Lastname</maintainer>
      <license>BSD</license>
      <url type="website">https://github.com/link/ros_</url>
      <author email="user@email.ch">Firstname Lastname</author>

      <buildtool_depend>catkin</buildtool_depend>

      <depend>roscpp</depend>
      <depend>sensor_msgs</depend>
</package>

More info

• http://wiki.ros.org/catkin/package.xml

:fa:file CMakeLists.txt

The CMakeLists.txt is the input to the CMake build system

1. Required CMake Version (cmake_minimum_required)
2. Package Name (project())
3. Find other CMake/Catkin packages needed for build (find_package())
4. Message/Service/Action Generators (add_message_files(), add_service_files(), add_action_files())
5. Invoke message/service/action generation (generate_messages())
6. Specify package build info export (catkin_package())
7. Libraries/Executables to build (add_library()/add_executable()/target_link_libraries())
8. Tests to build (catkin_add_gtest())
9. Install rules (install())

cmake_minimum_required(VERSION 2.8.3)
project(husky_highlevel_controller)
add_definitions(--std=c++11)

find_package(catkin REQUIRED COMPONENTS roscpp sensor_msgs )

catkin_package(
   INCLUDE_DIRS include
   # LIBRARIES
   CATKIN_DEPENDS roscpp  sensor_msgs
   # DEPENDS
)

include_directories(include ${catkin_INCLUDE_DIRS})

add_executable(${PROJECT_NAME} src/${PROJECT_NAME}_node.cpp src/HuskyHighlevelController.cpp)

target_link_libraries(${PROJECT_NAME} ${catkin_LIBRARIES})

More info

• http://wiki.ros.org/catkin/CMakeLists.txt

Eclipse integration

• Build the Eclipse project files with additional build flags

catkin build package_name --cmake-args -G"Eclipse CDT4 - Unix Makefiles” -D__cplusplus=201103L D__GXX_EXPERIMENTAL_CXX0X__=1

• To use flags by default in your catkin environment, use the catkin config command.
• The Eclipse project files will be generated in ~/catkin_ws/build

C++ Client Library

• http://wiki.ros.org/roscpp
• http://wiki.ros.org/roscpp/Overview

Example

#include <ros/ros.h>

int main(int argc, char** argv)                   // ROS main head file
{
   ros::init(argc, argv, "hello_world");         // has to be called before ROS func's
   ros::NodeHandle nodeHandle;                   // access poiunt for communication
   ros::Rate loopRate(10);                       // ros:Rate runs loops at desired freq e.g. 10 = 10 Hz

   unsigned int count = 0;
   while (ros::ok()) {                           // checks if a node should continue running
         ROS_INFO_STREAM("Hello World " << count); // ROS_info() logs messages from fs
         ros::spinOnce();                          // processes incommind msg via callbacks
         loopRate.sleep();
         count++;
   }
   return 0;
}

Node Handle

http://wiki.ros.org/roscpp/Overview/NodeHandles

// Default (public) node handle:      // Recommended
nh_ = ros::NodeHandle();              // /namespace/topic

// Private node handle:               // Recommended
nh_private_ = ros::NodeHandle("~");   // /namespace/node/topic

// Namespaced node handle:
nh_eth_ = ros::NodeHandle("hevs");    // /namespace/hevs/topic

// Global node handle:                // NOT Recommended
nh_global_ = ros::NodeHandle("/");    // /topic

Logging ROS_INFO

• http://wiki.ros.org/rosconsole
• http://wiki.ros.org/roscpp/Overview/Logging

Send text to log files and console. Instead of std::cout, use e.g. ROS_INFO.

Severity Levels

+------------+--------------------+--------------------+--------------------+--------------------+--------------------+ | | Debug | Info | Warn | Error | Fatal | +============+====================+====================+====================+====================+====================+ | stdout | :fa:check-circle | :fa:check-circle | | | | +------------+--------------------+--------------------+--------------------+--------------------+--------------------+ | stderr | | | :fa:check-circle | :fa:check-circle | :fa:check-circle | +------------+--------------------+--------------------+--------------------+--------------------+--------------------+ | Log file | :fa:check-circle | :fa:check-circle | :fa:check-circle | :fa:check-circle | :fa:check-circle | +------------+--------------------+--------------------+--------------------+--------------------+--------------------+ | /rosout | :fa:check-circle | :fa:check-circle | :fa:check-circle | :fa:check-circle | :fa:check-circle | +------------+--------------------+--------------------+--------------------+--------------------+--------------------+

Formatting Style

ROS_INFO("Result: %d", result);           // printf style
ROS_INFO_STREAM("Result: " << result);    // stream style

Launchfile

To see the output in the console set configuration to screen in the launch file.

<launch>
      <node name="listener" more="stuff" output="screen"/>
</launch>

Subscriber

http://wiki.ros.org/roscpp/Overview/Publishers%20and%20Subscribers

Start listening to a topic by calling the method subscribe() of the node handle

ros::Subscriber subscriber = nodeHandle.subscribe(topic, queue_size, callback_function);

Example

#include "ros/ros.h"
#include "std_msgs/String.h"

// callback function when a message is received
void chatterCallback(const std_msgs::String& msg) {
   ROS_INFO("I heard: [%s]", msg.data.c_str());
}

int main(int argc, char **argv) {
   ros::init(argc, argv, "listener");
      ros::NodeHandle nodeHandle;
      // Subscript to topic with a queue size of 10 (1-10 is recommended)
      ros::Subscriber subscriber = nodeHandle.subscribe("chatter",10,chatterCallback);
      ros::spin(); // stay's here forever
      return 0;
}

Publisher

http://wiki.ros.org/roscpp/Overview/Publishers%20and%20Subscribers

Create a publisher with help of the node handle

ros::Publisher publisher = nodeHandle.advertise<message_type>(topic, queue_size);

Example

#include <ros/ros.h>
#include <std_msgs/String.h>

int main(int argc, char **argv) {
      ros::init(argc, argv, "talker");
      ros::NodeHandle nh;
      // Node handle queue size of 1
      ros::Publisher chatterPublisher = nh.advertise<std_msgs::String>("chatter", 1);
      ros::Rate loopRate(10);

      unsigned int count = 0;
      while (ros::ok()) {
         std_msgs::String message;
         // Cretae message content
         message.data = "hello world " + std::to_string(count);
         ROS_INFO_STREAM(message.data);
         chatterPublisher.publish(message);
         ros::spinOnce();
         loopRate.sleep();
         count++;
      }
      return 0;
}

OOP

http://wiki.ros.org/roscpp_tutorials/Tutorials/UsingClassMethodsAsCallbacks

Example

#include <ros/ros.h>
#include "my_package/MyPackage.hpp"
int main(int argc, char** argv) {
      ros::init(argc, argv, "my_package");
      ros::NodeHandle nodeHandle("~");
      // Call
      my_package::MyPackage myPackage(nodeHandle);

      ros::spin();
      return 0;
}

+--------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------+ | class MyPackage | class Algorithm | +================================================================================+==============================================================================================+ | Main node class providing ROS interface (subscribers, parameters, timers etc.) | Class implementing the algorithmic part of the node | | | | | | Note: The algorithmic part of the code could be separated in a (ROS-independent) library | +--------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------+

Parameter Server

http://wiki.ros.org/roscpp/Overview/Parameter%20Server

Example Parameter File

camera:
   left:
      name: left_camera
      exposure: 1
   right:
      name: right_camera
      exposure: 1.1

Example Launch file

<launch>
      <node name="name" pkg="package" type="node_type">
         <rosparam command="load" file="$(find package)/config/config.yaml" />
      </node>
</launch>

C++ API

ros::NodeHandle nodeHandle("~");
std::string topic;
if (!nodeHandle.getParam("topic", topic)) {
   ROS_ERROR("Could not find topic parameter!");
}

Get a parameter in C++ with

nodeHandle.getParam(parameter_name, variable)

• Method returns true if parameter was found, false otherwise

• Global and relative parameter access:

• Global parameter name with preceding /

  nodeHandle.getParam("/package/camera/left/exposure", variable)
  

  Relative parameter name (relative to the node handle)

  nodeHandle.getParam("camera/left/exposure", variable)
  

  * For parameters, typically use the private node handle

  ros::NodeHandle("~")