URBI

Urbi

Developer(s)	Gostai
Initial release	2003 (2003)
Stable release	2.7.4 / November 17, 2011 (2011-11-17)
Repository	github.com/urbiforge/urbi
Written in	urbiscript, C++
Operating system	Microsoft Windows, Mac OS X, Linux
Type	Robotics suite, OS, library
License	GNU Affero GPL v3
Website	www.urbiforge.com

Urbi is an open source cross-platform software platform in C++ used to develop applications for robotics and complex systems. Urbi is based on the UObject distributed C++ component architecture. It also includes the urbiscript orchestration language which is a parallel and event-driven script language. UObject components can be plugged into urbiscript and appear as native objects that can be scripted to specify their interactions and data exchanges. UObjects can be linked to the urbiscript interpreter, or executed as autonomous processes in "remote" mode.

The urbiscript Language

Main article: urbiscript

The urbiscript language has been developed since 2003 by Jean-Christophe Baillie in the Cognitive Robotics Lab of ENSTA, Paris. It is now actively and further developed in the industry through the Gostai company founded in 2006.

The urbiscript language can be best described as an orchestration script language: like Lua in video games, urbiscript can be used to glue together C++ components into a functional behavior, the CPU-intensive algorithmic part being left to C++ and the behavior scripting part being left to the script language which is more flexible, easy to maintain and allows dynamic interaction during program execution. As an orchestration language, urbiscript also brings some useful abstractions to the programmer by having parallelism and event-based programming as part of the language semantics. The scripting of parallel behaviors and reactions to events are core requirements of most robotic and complex AI applications, therefore urbiscript (and the whole Urbi platform) is well suited to these applications.

Language attributes

• Parallelism and event-based programming
• Prototype-based programming
• C++ like syntax
• C++ based component architecture (UObject) with possibility to link objects or run them remotely
• Client/Server based architecture
• Client interfaces with Java and Matlab (Urbi SDK)
• Cross platform: Linux, Mac, Windows and others. Embeddable, URBI can run on various processors: x86, ARM, mips, powerPC, etc.
• Taggable commands for execution flow control

Pros

• Urbi is now open source with a GPL compatible license (GNU AGPL v3) since May 2010.
• Urbi is interoperable with Willow Garage's ROS.
• Supported by a company if support is needed, frequent releases, and a core dev team.

Cons

• Urbi can be used as a simple C++ middleware, without urbiscript. However, using urbiscript requires learning a relatively new language, not so much in term of syntax (which is C-like), but rather in terms of parallel/event-based programming paradigm.
• Software for visual robot control Gostai Studio and Gostai Lab are proprietary and not free.

Examples

The example below shows how to write a ball tracking action/perception loop in urbiscript: headYaw/headPitch are two motor objects, and ball is the ball detection object (x and y range from -1/2 to 1/2):

 whenever (ball.visible)
 {
     headYaw.val   += camera.xfov * ball.x
   &
     headPitch.val += camera.yfov * ball.y
 };

whenever is used to trigger a piece of code in loops as long as the associated condition is true. The "&" sign is used to specify that both commands should start at the same time, thus running in parallel.

Other notable event-driven constructs include at, which triggers the associated code once when the event is triggered:

 at (speech.hear?("hello"))
 {
   voice.say("How are you?") &
   robot.standup();
 }

Every command or group of commands is taggable, which provides a way to stop it later if needed:

 myTag:
   while (true)
     echo("This is a never ending loop"),
 at (button.pressed)
   myTag.stop;

Note in the example above the comma at the end of the command. It will put the preceding command in background, allowing the flow execution to carry on, in particular the next 'at' command to be executed.

UObject component architecture

The UObject component architecture, currently based on the C++ UObject library, allows developers to interface any C++ object within Urbi, making selected methods and attributes visible in the script language, while in fact being C++ code. Special notifiers can be set on any of the object's attributes to notify the C++ side of any change on these attributes on the urbiscript/Urbi side.

UObject uses C++ templates to transparently map any requested method to an interface machinery that takes care of the type checking.

A C++ UObject can be used in plugged mode if it is directly linked to the URBI Engine at compile time or with dynamic loading. In that case, the C++ object shares the Urbi Kernel memory directly, resulting in efficient integration. This is typically used for time critical components like motor or sensor drivers. The same C++ UObject can also be used without modifications as a remote component. In that case, it will become an autonomous program to be executed with the IP address of the Urbi server as a parameter. In both cases, the object will transparently appear in urbiscript as a native urbiscript object.

Components for Robotics: speech, face/object detection, SLAM

Gostai has several plug & play UObject components useful for robotics:

• voice recognition
• voice synthesis
• face detection (including a bridge with OpenCV)
• face recognition
• SLAM
• color blob detection
• SIFT based object recognition

Free GPL components developed by the community can be found and exchanged on the urbiforge community website of URBI.

Ecosystem

Robotics simulators compatible with Urbi

• Webots is the official robot simulator compatible with Urbi ,.
• Player/Stage integration has been reported, although it is not currently released.

"Urbi-fied" robots

Released:

• Segway
• Aibo ERS7/ERS2xx (Urbi 1.x only)
• iRobot Create
• Lego Mindstorms NXT[1]
• HRP-2 (restricted release to members of JRL)
• Nao
• Robotis Bioloid
• Mobile Robots Pioneer

Announced:

• Surveyor
• Khepera III
• e-puck

Development environments

Urbi comes with Gostai Studio that integrates a behavior editor to graphically create finite state machines whose states are simple urbiscript programs, and GUI builder to design interfaces with drag and drop support. Gostai Studio is cross-platform and generates freely usable urbiscript code as an output. Choregraphe is a platform for NAO using Python and also URBI languages.

See also

• Robotics suite
• Player Project - open source robot interface in research and post-secondary education
• ROS (Willow Garage)

External links

• Official website
• Urbi Online documentation
• urbiscript Tutorial
• UObject Tutorial
• Videos
• Wong, William, "Gostai Urbi", "Electronic Design", August 05, 2010.
• McCafferty, Billy, "Q&A of Urbi, a robot OS", "Sharprobotica", July 16, 2010.
• Blankenhorn, Dana, "I, open source robot", "ZDNet", August 20, 2010.