Architecture

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In order to address the requirements and resolve the current issues with Gazebo, we propose a distributed architecture. Gazebo will be broken into libraries for physics simulation, rendering, user interface, communication, and sensor generation. Three different processes will be provided: physics_sim, sensor_gen, gui, and a master for coordination.

Contents

Communication Between Processes

Communication between each process will use a combination of google::protobufs and sockets. The communication architecture will mimic that of ROS nodes. A simulated world will publish body pose updates, and sensor generation and GUI will consume these messages to produce output.

This mechanism will allow for introspection of a running simulation, and provide a convenient mechanism to control aspects of Gazebo.

System Diagram

Gazebo design.png

Gazebo Master

This is a stripped down clone of the ROS master. It provides namelookup, and topic management. A single master can handle multiple physics simulations, sensor generators, and GUIs.

Communication Library

  • Dependencies: Protobuf and boost::ASIO
  • External API:
  • Internal API: None
  • Advertised Topics: None
  • Subscribed Topics: None

This library is used by almost all subsequent libraries. It acts as the communication and transport mechanism for Gazebo. It currently supports only publish/subscribe, but it's possible to use RPC with minimal effort.

Physics Library

  • Dependencies: Dynamics engine, and Collision Library
  • External API: Provides a simple and generic interface to physics simulation
  • Internal API: Defines a fundamental interface to the physics library for 3rd party dynamic engines.

The physics library can use any dynamic engine that conforms to the internal API (TBD). It also presents a simple external interface in order to establish a work physics simulation.

Collision Library

  • Dependencies: 3rd party collision engine
  • External API: TBD
  • Internal API: Generic interface for collision engines
  • Advertised Topics: None
  • Subscribed Topics: None

This is an abstraction library to handle different collision engines, and provide a simple external interface to the user.

Rendering Library

  • Dependencies: OGRE
  • External API: Allows for loading, initialization, and scene creation
  • Internal API: None, we are going to use only OGRE.

The rendering library provides a simple interface to both the GUI and sensor generation. We are currently sticking with OGRE since we don't have a better alternative. It will be possible to write plugins for the rendering engine.

Sensor Generation

  • Dependencies: Rendering Library, Collision Library
  • External API: Provide functionality to initialize and run a set of sensors
  • Internal API: TBD

The sensor generation library implements all the various types of sensors, listens to world state updates from a physics simulator and produces output specified by the instantiated sensors.

GUI

  • Dependencies: Rendering Library, wxWidgets
  • External API: None
  • Internal API: None

The primary function of the GUI involves displaying the current state of the simulation and providing a convenient means for user input. There is no need for an internal or external API since we are sticking with wxWidgets.

Plugins

The physics, sensor, and rendering libraries will support plugins. These plugins will provide users with access to the respective libraries without using the communication system.

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