introduction to ros · 2018-04-12 · introduction to ros lasse einig, dennis krupke, florens...

MIN FacultyDepartment of Informatics

Introduction to ROS

Lasse Einig, Dennis Krupke, Florens Wasserfall

University of HamburgFaculty of Mathematics, Informatics and Natural SciencesDepartment of Informatics

Technical Aspects of Multimodal Systems

April 10, 2018

L. Einig, D. Krupke, F. Wasserfall – ROS Introduction 1 / 23

OutlineFoundation Structure Communication Kinematics Tool

FoundationStructureCommunicationKinematics Tool


MotivationFoundation Structure Communication Kinematics Tool

I Heterogeneity vs. HomogeneityI sensor types, actuators, ...I sensor model, kinematic chain, ...

I AbstractionI Algorithm re-usability

I 2D laser data mappingI object recognition

I DebuggingI simulation, data visualization, ...


IdeaFoundation Structure Communication Kinematics Tool

I Robot Operating SystemI Meta operating systemI Open sourceI Hardware abstraction

I portabilityI simplification of sensors and actuators

I Recurring tasks already solvedI Navigation, data filtering, object recognition ...


Current StateFoundation Structure Communication Kinematics Tool

I Multiple versions actively usedI may not be compatible to each otherI may not provide same libraries

I Linux (Ubuntu!)I Supports C/C++, Python, Java, Lisp, Octave ...

I Python for high level code/fast implementationI C/C++ for algorithms/computation

I Functions and algorithms already availableI May be difficult to findI Better than reimplementing


ROS SystemFoundation Structure Communication Kinematics Tool

I ROS nodesI sensorsI actuatorsI logic

I ROS coreI Communication


ROS NodeFoundation Structure Communication Kinematics Tool

I Discrete part of the systemI Specialized software/algorithmI Many ROS nodes per systemI Example:

I node gets imageI runs edge detection algorithm on itI provides found edges


ROS CoreFoundation Structure Communication Kinematics Tool

I Central unit, also called ROS masterI nodesI sensorsI communication

I Coordination of nodesI Communication ManagementI Exactly one per systemI Transparent to the user


CommunicationFoundation Structure Communication Kinematics Tool

I MessagesI standardized data types

I TopicsI n:n communication

I Services and ActionsI 1:1 communication


SensorsFoundation Structure Communication Kinematics Tool

I ExplorationI LocalizationI DetectionI One node per sensor

I provide data as topicI abstract from hardware


System structureFoundation Structure Communication Kinematics Tool

applications fetch beercapabilitiesuniverse navigation; arm; grasping

libraries tf; pcl; opencv; bullet; eigentools rxgraph; rostopic; roslaunch

middlewaremain rosmaster; roscpp; rosbuild

I universe : robot centric, developed by communityI main : general tools, maintained by OSRF



FoundationStructureCommunication

MessagesTopicsServicesActions

Kinematics Tool


MessagesFoundation Structure Communication Kinematics Tool

I Fundamental communication conceptI Description of data setI Data types

I ROSI general

I HeaderI time stampI identifier

$ rosmsg show -r robot_msgs/Quaternion# xyz - vector rotation axis, w - scalar term (cos(ang/2))float64 xfloat64 yfloat64 zfloat64 w


TopicsFoundation Structure Communication Kinematics Tool

I Published by nodesI Unique identifierI AnonymityI Open subscriptionI Sensor data


Communication – ExampleFoundation Structure Communication Kinematics Tool

ROS master

camera viewer



ROS master

camera viewer

advertise(’images’)



ROS mastertopic:images

camera viewer




camera viewer

subscribe(’images’)




camera viewerimages(tcp)




camera viewer

publish(img)

images(tcp)




camera viewer

processorpublish(img)

images(tcp)




camera viewer


subscribe(’images’)

images(tcp)




camera viewer


images(tcp)

images(tcp)


ServicesFoundation Structure Communication Kinematics Tool

I 2 message typesI request and response

I Synchronous protocolI client sends requestI client waits for serverI server replies

$ rosservice type add_two_ints | rossrv showint64 aint64 b- - -int64 sum




camera viewer

processor

client

publish(img)

images(tcp)

images(tcp)




camera viewer

processor

client

publish(img)

wait_for_service(’process’)

images(tcp)

images(tcp)




camera viewer

processor

client

publish(img)

wait_for_service(’process’)Service(’process’,srv.Proc)

images(tcp)

images(tcp)




service:process

camera viewer

processor

client

publish(img)

images(tcp)

images(tcp)




service:process

camera viewer

processor

client

publish(img)

ServiceProxy

(’process’,srv.Proc)

images(tcp)

images(tcp)




service:process

camera viewer

processor

client

publish(img)

request

images(tcp)

images(tcp)




service:process

camera viewer

processor

client

publish(img)

images(tcp)

images(tcp)




service:process

camera viewer

processor

client

publish(img)

response

images(tcp)

images(tcp)


ActionsFoundation Structure Communication Kinematics Tool

I 3 message typesI goal and resultI optional feedback

I Asynchronous protocolI client sends goalI server may respond with feedbackI server delivers result

I Interruptible

# Define the goaluint32 dishwasher_id # Specify which dishwasher we want to use- - -# Define the resultuint32 total_dishes_cleaned- - -# Define a feedback messagefloat32 percent_complete




service:process

camera viewer

processor

client

publish(img)

images(tcp)

images(tcp)




service:process

camera viewer

processor

client

publish(img)

ActionClient

(’process’,ProcAction)

images(tcp)

images(tcp)




service:process

camera viewer

processor

client

publish(img)

wait_for_server(’process’)

images(tcp)

images(tcp)




service:process

camera viewer

processor

client

publish(img)

wait_for_server(’process’) ActionServer(’process’,ProcAction)

images(tcp)

images(tcp)




service:processaction:process

camera viewer

processor

client

publish(img)

images(tcp)

images(tcp)





camera viewer

processor

client

publish(img)

goal

images(tcp)

images(tcp)





camera viewer

processor

client

publish(img)

feedback(20%)

images(tcp)

images(tcp)





camera viewer

processor

client

publish(img)

feedback(40%)

abort

images(tcp)

images(tcp)





camera viewer

processor

client

publish(img)

feedback(60%)

images(tcp)

images(tcp)





camera viewer

processor

client

publish(img)

feedback(80%)

wait_for_result

images(tcp)

images(tcp)





camera viewer

processor

client

publish(img)

result

images(tcp)

images(tcp)


Kinematics ToolFoundation Structure Communication Kinematics Tool

I Visualization for kinematics of robot models


PropertiesFoundation Structure Communication Kinematics Tool

I Obeys physical constraints of the robot modelI Based on 100 Hz control loopI Forward control by sending joint target messagesI Offers IK solving serviceI Simple setupI Programmable in Python and C++

I Samples only in Python


introduction to ros · 2018-04-12 · introduction to ros lasse einig, dennis krupke, florens...

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