Robot Operating System (ROS)Tools in ROS rxgraph display a visualization of a ROS computation graph client library supports the development of nodes allows easy access to topics, paramter,

Gerald Steinbauer

Institute for Software Technology

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Advanced Robotics - ROS

Advanced RoboticsRobot Operating System (ROS)

Gerald SteinbauerInstitute for Software Technology

Gerald Steinbauer


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Robot Operating System (ROS)

• framework for the development of robot software

• provides OS-like functionality• originally developed by Stanford AI Lab

(SAIL)• meanwhile maintained by Willow Garage

and Open Source Robotics Foundation• open source robotics framework• used by several leading robotics labs• provides a lot of functionality on various

levels

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runs on several robot platforms

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provides a lot of functionality

• many research groups provide their results as open source ROS packages:• motion planning and navigation• localization• exploration and mapping• arm navigation and object manipulation• 3D perception and object manipulation• high-level control and knowledge representation• …

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Design Principles of ROS

• peer-to-peer– several independent processes and hosts

• multi-lingual– communication is based on XML-RPC– supports C++, Phyton, Octave, LISP– defined data types, proprietary message definition files

• tool-based– Linux philosophy with small building blocks

• thin– functionality is packed in stand-alone libraries, also 3rd party– uses its own build system

• open-source

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OS

ROS

MessagePassing

WordProcessing

Web Browser

GUIMemoryManagement

File System Scheduler Drivers

Visualization

NavigationTask Executive

Simulation Manipulation

ClientLibratries

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ROS - Operation

• ROS is definitely on the operation side• supports message transport

• publisher/subscriber (nodes, messages, topics)• client/server (services, action-server)

• runtime execution• threads and related techniques• configuration

• supports development• reusable classes and libraries• definition of interfaces• debugging, logging and visualization tools• build system

• …

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ROS Eco-System I

universe

main

robot centric

general

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ROS Eco-System II

capabilities

middleware

navigation, arm, grasping

toolsuniverse

main

libs

apps fetch beer

tf, pcl, opencv, bullet, eigen

rxgraph, rostopic, roslaunch

rosmaster, roscpp, rosbuild

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Beer Me (Bottom Up)

middleware

capabilities

tools

libs

appsBeerMe

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Beer Me (Top Down)

BeerMe

Open FridgeDelivery

Face Recognition

BeerIdentification

PCL

TF

navigation OpenCV SMACH

arm navigation web interface collision space

roscpp common_msg rospyrosmasteractionlib

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ROS Versions• ROS Box Turtle (March 2010)

• ROS C Turtle (August 2010)

• ROS Diamondback (March 2011)

• ROS Electric Emys (August 2011)

• ROS Fuerte Turtle (April 2012)

• ROS Groovy Galapagos (December 2012)

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File Organisation in ROSa package is an organization unit in ROS

the goal is to provide functionalityit can contain a node, a library, data,

configurations …

a manifests provide metadata about a package, including its license information and dependencies, as well as language-

specific information such as compiler flags

stacks are collections of packages that provide aggregate functionality, such as a

"navigation stack"

stack manifests provide data about a stack, including its license information and

its dependencies on other stacks

a bag is a file format in ROS for storingROS message data

repositories are collections of stacks, usually the common code base of an

institution

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Building Blocks of ROSa node is an executable that uses ROS to communicate with other nodes and does

computation

nodes can publish messages to a topic as well subscribe to a topic to receive

messages (many-to-many communication)

messages are ROS data type used when subscribing or publishing to a topic

a service is a node with one defined input and one defined output message type

the master is a node that is the name service for ROS

it helps nodes find each other nodes

rosout is the decentralized ROS equivalent of stdout/stderr

the parameter server provides and manages parameter across the network

roscore is master + rosout + parameter server

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Naming in ROS

• hierarchical naming structure• used for all resources

• nodes• parameter• topics• services

• nodes may have a name space/node_name/topic_name

• parameter are hierarchically organized as well/p3at/odometry/frequency

• can be used like a Linux file system (relative, global)

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Navigation the ROS File System

• a number of command-line tools makes live easier• changing into a package directory

• roscd package_name

• building a package• rosmake (package_name)

• Running a node• rosrun package_name node_name

• running a larger project• roslaunch launch_file

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Publisher – Subscriber Communication

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Synchronous Service

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Actions

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Action Interface

ActionClient

ActionServer

goalcancel

statusstatus

feedback

from client

from server

action protocol relies on ROS topics to transport messages

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Messages• simple data structures that are passed between nodes• defined in package-name/msg/*.msg files, sent over topics• basic data types:

• int{8,16,32,64}• float{32,64}• string• time• Duration• array[]

• Example: Point:msg• float64 x• float64 y• float64 z

• used in ROS services, defined in package-name/srv/*.srv Service = Request msg + Response msg

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Parameters

• have unique names• can represent primitive data types:

• integers• floats• boolean• dictionaries• maps, etc

• can be set and remapped at runtime• stored on the parameter server• dynamic reconfiguration – notify nodes about

parameter changes

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Parameter Setting

• nodes can set parameters on the server• any other nodes can read them• also command-line tool

Talker Listener

ROS Master

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Working with Topics

• the command-line tools rostopic makes live easier• list all available topics

• rostopic list

• showing messages on a topic• rostopic echo topic_name

• showing message type of a topic• rostopic type topic_name

• …

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Computation Graph

robot laser imu map

localization

pathplanner

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Tools in ROS

rxgraph display a visualization of a ROS computation graph

client library supports the development of nodes

allows easy access to topics, paramter, …C++ & Phyton

rviz is a 3d visualization toolit is online configurable and is able to

display sensor data, point clouds, paths, coordinate systems

ROS is able to record and playback all topics in an transparent way and in the

proper timing

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ROS - Function

• ROS supports the functional view to some extend• behavioral control

• local path planner• obstacle avoidance• trajectory generation

• executive• global path planner• SMACH – state machine for task-level control

• planning• Cognitive Robot Abstract Machine (CARM) by TUM• Knowledge Processing for Autonomous Personal Robots

(KnowRob) by TUM

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Launch Files

• it’s a pain to start up larger project form scratch at the command-line

• the tool roslaunch allows to script start up procedures• allows to specify nodes, configurations, renaming …• follows a XML-syntax<launch>

<param name="foo" value="$(optenv NUM_CPUS 1)" /><param name=“foofile" value="$(find foo_pkg)/foo.xml" /><node name=“foo" pkg=“foo_pkg" type=“foo.py" />

</launch>

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tf

• robots usually have a number of data (2D and 3D senor data, poses, …) in various static and variablecoordinate systems

• data in ROS are relative to a coordinate system called “frame”

• data stay in their producing frame• data are transformed in a target

frame on purpose only• the tf library and a set of tools take

care about transformations

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Transformation Basics

+X

+Y

+Z

roll

pitch

yaw

right hand ruleroll, pitch, yaw

Euler angles

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Transform Chains

• frames can build transformation chains• tree-like structure• transformation between any frames automatically

calculated by tf – if connected by a tree (forest is possible too)

[Andreasson et al. 2008]

map kinectframe

laserframe

plateframe

baseframeodometry

frame

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Transformation Tree

odom base_linklaser_base_link

kinect_base_link

map

plate_link

odom

kinect:_base_linklaser_base_link

base_link

map plate_link

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Transformation Transport

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tf tools• in program code

• instantiate a transform listener• retrieve transformation for particular frames and time stamps• transform data

• tf_echo• command-line tool to display transformation messages for particular frames

• tf_monitor• command-line tool to display all transformation messages

• rviz• graphical tool to visualize all kind of data and robots

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Useful Features in ROS

• coordination transformation with tf– manage several reference frames– automated conversion

• unified data types for similarsensors and actuators– e.g. point clouds for laser scanner– e.g. velocity_command for robot

platforms

• remote access from other hosts– transparent network

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Supported Hardware

• ROS provides a huge and continuously growing set of standard nodes for robots und sensors– Willow Garage PR2– Pioneer Robot Family– Aldebaran Nao– Lego NXT– Festo Robotino– Sick Laser Scanner Family– Hokuyo Laser Scanner– GPS (NMEA)– Katana Arm– Cameras with various interface– Microsoft Kinect– ….

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Functions in ROS• mapping (gmapping)

– based on the free gmapping– simple generation of 2d maps

• navigation– complete navigation stack– allows autonomous navigation

• arm navigation based on OMPL

• organization of behaviors– standard templates for behaviors

(actionlib)

• decision making– finite state machine (SMACH )

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Additional Information

• Ros wiki (http://www.ros.org/wiki/)• Ros answers (http://answers.ros.org)• Ros tuorials (http://www.ros.org/wiki/ROS/Tutorials)

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Questions?Thank you!

Robot Operating System (ROS)Tools in ROS rxgraph display a visualization of a ROS computation graph client library supports the development of nodes allows easy access to topics, paramter,

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