Nate Koenig

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Stage and GazeboThe Instant Experts Guide

• Nate Koenig
• 15 Sep 2004

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Overview

• Simulators
• When, why, how, what
• The right tool Stage or Gazebo?
• Stage in depth
• Installation, usage
• Examples
• Gazebo in depth
• Installation and usage
• Examples
• Where to get help

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Working with Simulators

• What
• Mimic the real world, to a certain extent
• When
• Always!!
• Why
• Save time and your sanity
• Experimentation much less destructive
• Use hardware you dont have
• Create really cool videos
• How
• Someone has probably already done it, so use it

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Which Simulator?
Gazebo 3D Sensor-based Player Dynamic
O(n) O(n3) Small teams (10s)
Stage 2D Sensor-based Player interface
Kinematic O(1) O(n) Large teams (100s)
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The Big Picture
Stage
TCP/UDP
Cmds
Player
Gazebo
Client
Data
SHM
Real Hardware
TCP/UDP
TCP/UDP
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Stage
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Stage Environment

• Simulates mobile robots, sensors and objects on
  2-D bitmapped environment

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Stage Models

• Designed for multi-agent autonomous research
• Each model simple (computationally cheap)
• Can simulate many such models

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Stage Control

• Control models via Player
• Simulated hardware appear as their real
  counterparts
• Easy transition between simulation and real world
• Supports a wide range of devices
• Pioneers, laser, sonar, camera, pucks, etc.

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Stage In Depth

• The result?

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Stage Worldfile

• Stage environment specified in a worldfile
• Describes the robots, sensors and objects
• Many examples provided in distribution

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Example Stage Worldfile
the resolution of Stage's raytrace model in
meters resolution 0.02 GUI settings gui (
size 502.000 506.000 origin 5.018 4.950
0 scale 0.021 the size of each bitmap pixel
in meters ) load a bitmapped environment from
a file bitmap ( file "cave.pnm.gz"
resolution 0.02 ) include "pioneer.inc
create a robot, set start position and Player
port, and equip it with laser scanner position (
port 6665 pose 1.0 1.0 20 laser() )
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Running Stage

• To run stage
• Note Stage automatically starts a player server
• Problem abstract devices not implemented in
  Stage are needed. Such as VFH, or AMCL
• Solution start another Player server using
  passthrough devices
• Passthrough devices send data/cmds between Player
  servers
• A secondary server can collect data from Player,
  and run abstract devices

stage ltmyworldgt
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Working With Stage
Stage
Player localhost8000
Controller (client)
position0 port 7000 laser0
position0 driver passthrough port
7000 laser0 driver passthrough port
7000 position0 driver vfh position_index 0
laser_index 0 port 7000
Controller (client)
TCP/UDP
TCP/UDP
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Gazebo
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Gazebo In Depth

• Simulates robots, sensors, and objects in a 3-D
  dynamic environment
• Generates realistic sensor feedback and physical
  interactions between objects

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Gazebo In Depth

• Gazebo aims to be a high fidelity simulator
• Each model is NOT computationally cheap
• Small robot populations are possible.
• Dependent on number and type of robots

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Exception to the rule
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Gazebo Architecture
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Gazebo Architecture
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Gazebo Architecture
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Gazebo Client Code

• Client code (your program), can interface to
  Gazebo in two ways
• libgazebo
• Shared Memory, direct interface
• Fast, but requires more work
• Player
• Simulation transparency
• Get all of Players goodies
• Easier, but with more computational overhead
• Recommended for most cases

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Gazebo Architecture
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Libgazebo

• Simple C library
• Treat as a blackbox
• Client and server must run on same machine
• Read sensor data and send commands to simulated
  devices
• Devices and Interfaces
• Devices (Model), represent real world objects
• Pioneer2AT, SickLMS200
• The objects within Gazebo simulation
• Interfaces are general specifications for entire
  classes of devices
• Position, Laser
• The programmatic hooks to devices

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Gazebo Architecture
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The World

• A world is composed of a model hierarchy
• Models define simulated devices
• Models can be nested
• Specifies how models are physically attached to
  one another
• Think of it as bolting one model to another

ltmodelPioneer2ATgt ltidgtrobot1lt/idgt
ltmodelSickLMS200gt ltidgtlaser1lt/idgt
ltxyzgt0.10.0 0.2lt/xyzgt lt/modelSickLMS200gt lt/m
odelPioneer2ATgt

• Worldfile snippet
• Pioneer with a sick laser attached
• Sicks ltxyzgt relative location to Pioneer

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Gazebo Architecture
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Models

• Each model contains a few key properties
• Physical presence (optional)
• Body sphere, box, composite shapes
• Kinematics joints, velocities
• Dynamics mass, friction, forces
• Appearance color, texture
• Interface (optional)
• Control and feedback interface (libgazebo)

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Types of Models

• Static Models
• Built into Gazebo statically linked into server
• In general such models added by lead developers
• Plugin Models
• Shared objects loaded at runtime. Akin to linux
  kernel modules
• Recommended for new, experimental, third-party
  models
• Easier to build, faster code/compile/test cycle,
  source can be maintained in separate repository

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Available Models

• Factory
• GarminGPS
• GroundPlane
• LightSource
• MapExtruder
• ObserverCam
• Pioneer2AT
• Pioneer2DX
• Pioneer2Gripper
• Pioneer2Sonars
• SegwayRMP
• SickLMS200
• SimpleSolid
• SonyVID30
• Terrain
• TruthWidget

MapExtruder

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Working with Player

• Steps to creating a simulation
• Write Gazebo worldfile
• Start Gazebo
• Write corresponding Player configuration file
• Start Player
• Start client program
• Note
• Gazebo must be started before Player
• Player must be re-started whenever Gazebo is
  restarted

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Example Using a single robot

• Single robot with a scanning laser range finder

driver ( name "gz_position" devices
"position0" gz_id "robot1_position" )
driver ( name "gz_laser" devices
"laser0" gz_id "robot1_laser" )
ltmodelPioneer2DXgt ltidgtrobot1_positionlt/idgt
ltxyzgt0 0 0.40lt/xyzgt ltrpygt0 0 45lt/rpygt
ltmodelSickLMS200gt ltidgtrobot1_laserlt/idgt
ltxyzgt0.15 0 0.20lt/xyzgt ltrpygt0 0
0lt/rpygt lt/modelSickLMS200gt lt/modelPioneer2D
Xgt
Gazebo world
Player config
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Example Using a single robot

• Run Gazebo
• Run Player
• Now run your code

gazebo ltmyworldgt
player g default ltmyconfiggt
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Getting Player/Stage/Gazebo

• Source distributions from the Player/Stage
  website
• http//playerstage.sourceforge.net/
• No binary (pre-built) distributions
• Basic requirements
• Posix-like OS (Linux, OS X)
• GCC
• Gazebo additional requirements
• OpenGL with hardware acceleration
• Open Dynamics Engine (www.ode.org)

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Installing Packages

• To use Gazebo
• Download, install
• librtk-src-2.2.0
• gazebo-src-0.2.0
• player-src-1.4rc1
• To use Stage
• Download, install
• librtk-src-2.2.0
• player-src-1.3.2
• stage-src-1.3.2

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Getting Help

• Where to get help
• Your peers
• Player/Stage website
• Player/Stage/Gazebo mailing list archives
• Player/Stage/Gazebo mailing lists

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Questions?