Author: Pablo Iñigo Blasco Grupo de Investigación RTCAR Robotica y Tecnología de Computadores Universidad de Sevilla

1. Distributed Architecture,
Deployment and Introspection
Pablo Iñigo Blasco
Grupo de Investigación RTCAR
Robotica y Tecnología de Computadores
Universidad de Sevilla

3. Contents
● Distributed Architecture
● ROS Architecture
● Nodes
● Communication mechanisms
● Introspection Tools

4. Complex Robotic Software
Architectures
● Non-Functional requirements
● Ubiquity
● High computation power
● Real Time
● Fault Tolerance and Robustness
● Problems
● Integration Problems
● Deployment and Debugging Problems → Need of
complex and powerful tools

5. Problems
● Deployment Problems
● Multiple cpus, multiple cores
● Multiple computers distributed in a network
● Software Engienering related (scalability, reusability, etc.)
● Integration of huge sets of software technologies
● Need of Package reutilization (impossible reinvent the wheel)
● Libraries
● Programming languages

6. ROS Distributed Architecture
● Hybrid P2P Architecture
● Distributed Components
● Severals Node communication
mechanisms (message passing based)
● Focused on node communication
mechanisms
● Free internal node design

7. Nodes (I)
Parameters(*)
● Minimal building block
● Own control flow
Services
● Operative system process
● Reactive and/or proactive NODE
● Any supported language
● Communication mechanisms
● Services
● Topics
● Parameters
Startup
Topics
configuration
.yaml

8. Nodes (II) Example
Parameters
P 1.0
I 1.0
D 1.0
Services
goHome
shutdown
Dyxinamel Servo
Startup_config.yaml
current_pose
P 1.0
I 1.0
D 1.0
goal

9. ROS Distributed Architecture (II) -
Example
Computer A Computer B
RPC RPC
Node services services Node
topic
Node
Central Node Node
Node
topic
Actuators

10. ROS Distributed Architecture:
Pros & Cons
● Advantages:
● Paralelism
● Ubiquity
● Fault Tolerance
●
Modularity – low coupling
● Language Abstraction
●
Disadvantages:
● Real Time applications
●
Heavier Robotic Systems
● Additional requirements:
● Deployment tools for distributed architecture
● Distributed logging System
●
Remote Introspection Tools
●

11. Message
● Data Structure
my_package/msg/example.msg
● Message Interface Description
File string field1
int8 field2
● Code generation bool field3
other_pkg_msg/custom_msg field4
● Specific language proxy code
generation
● C++, Python..
● Conveys
● Message packages
●
●
geometry_msgs
sensor_msgs
.h
.h .py .java
● navigation_msgs

12. Messages (II) – Example
$ rospack find geometry_msgs`/msg
Point32.msg PoseWithCovarianceStamped.msg
Polygon.msg Transform.msg
PoseArray.msg TwistStamped.msg
PoseWithCovariance.msg Vector3.msg
WrenchStamped.msg
QuaternionStamped.msg
PointStamped.msg
Twist.msg
Pose2D.msg
TwistWithCovarianceStamped.msg
PoseStamped.msg
Wrench.msg
Quaternion.msg
Point.msg
TransformStamped.msg
PolygonStamped.msg
TwistWithCovariance.msg
Pose.msg
Vector3Stamped.msg
●

13. Message (III) Examples
geometry_msgs/PoseWithCovariance sensor_msgs/LaserScan
Header header
geometry_msgs/Pose pose
uint32 seq
geometry_msgs/Point position
time stamp
float64 x
string frame_id
float64 y
float32 angle_min
float64 z
float32 angle_max
geometry_msgs/Quaternion orientation
float32 angle_increment
float64 x
float32 time_increment
float64 y
float32 scan_time
float64 z
float32 range_min
float64 w
float32 range_max
float64[36] covariance float32[] ranges
float32[] intensities

14. Topics
● Publish/Subscribe Models
● Proactive nodes (agents)
● NxM
● Promotes the instrospection
mechanisms
● Asynchronous
● Several configurations (buffer,
latching, etc.)
● Underlying Transport Layer:
● TCP, UDP, Shared Memory
● Others Transport → rosserial,
ethercat

15. Services
● RPC my_package/srv/example.srv
● Purely Reactive string request_field1
int8 request_field2
---
● Request/Response string response_field1
other_pkg_msg/custom_msg response_field2
● Stable Functionality
Interface
● Specific language
proxy code generation
● C++, Python.. .h
.h .py .java
● Typical in others RSFs

16. ROS MASTER
● Hybrid P2P Distributed
Architecture
● Central Information Node
● Capabilities
● Parameter Server
● Resource Localization (White
Pages)
● Service Lookup (Yellow Pages)

17. Nodelets
● Threads
● Compatible node
communication nl
nl
mechanisms NODE
nl
● Zero copy
communication
between nodelets
● Share Machine
NODE
● Only C++

18. Macro - Components (Components
of Components)
Robot A Robot B
Launch Launch
Ros
Robot C Launch Master
Launch

19. Parameters
● Client/Server Model
● Common Variable Information
● Not automatically update inside nodes
● Can be seen as node properties thanks to the
ramming convention

20. Advanced mode communication
mechanisms
● Actions
● Dynamic Reconfigure
● (Custom) Based on state machines and
workflows (SMACH)
● They are based on basic primitives
● Nodes
● Parameters
● Services

21. Actions
● Preemptive tasks
● Non immediate tasks
● Cancelable tasks
● Based on topics
● Examples
● Moving the robot to a target
location
● Performing a laser scan and
returning the resulting point
cloud
● Detecting the handle of a
door

22. Deployment: Launch Files
● Deployment layout of building blocks (nodes)
● Naming pushing
● Startup configuration (direct or yaml files)
● XML syntax
● Itself can be seen as an complex component or
building block

23. Tools - Remote Introspection
● Topics (rostopic)
● Services (rosservice)
● Nodes (rosnode)
● Parameters (rosparam)
● Messages (rosmsg)
● Services (rossrv)
● General debugging (roswtf)

24. Tools - RX-Graph

25. DEMO AMCL

26. Introspection tools - Rxplot
● Monitor numerical data field at runtime
● Example
$ rxplot /odom/pose/pose/position/x /odom/pose/pose/position/y

27. Introspection tools - Rviz
● Graphical
Representation of
message
● Typical messages
visualization plugins

28. DEMO AMCL

29. References
(1) Iñigo-Blasco, Pablo, Fernando Diaz-del-Rio, Ma Carmen Romero-Ternero, Daniel Cagigas-Muñiz, and Saturnino
Vicente-Diaz. 2012. “Robotics software frameworks for multi-agent robotic systems development” Robotics and
(2) ROS Wiki - http://ros.org
(3) Quigley, Morgan, Brian Gerkey, Ken Conley, Josh Faust, Tully Foote, Jeremy Leibs, Eric Berger, Rob Wheeler,
and Andrew Ng. 2009. ROS: an open-source Robot Operating System. In Open-Source Software workshop of
the International Conference on Robotics and Automation (ICRA). Autonomous Systems (February).