Planning Scene Monitor

The planning scene is an object used for storing the representation of the world around the robot and also the state of the robot itself. The internal state of the planning_scene object is typically maintained by a planning_scene_monitor component that enables reading and writing the state in a thread-safe manner.

Particularly, the move_group node as well as the rviz planning scene plugin maintain their own Planning Scene Monitor (PSM). The move_group node’s PSM listens to the topic /planning_scene and publishes its planning scene state to the topic monitored_planning_scene. The latter is listened to by the rviz planning scene plugin.

World Geometry Monitor

The world geometry monitor builds world geometry using information from the sensors on the robot such as LIDARs or depth cameras and from user input. It uses the occupancy map monitor described below to build a 3D representation of the environment around the robot and augments that with information on the planning_scene topic for adding object information.

3D Perception

3D perception in MoveIt is handled by the occupancy map monitor. The occupancy map monitor uses a plugin architecture to handle different kinds of sensor input as shown in the Figure above. In particular, MoveIt has inbuilt support for handling two kinds of inputs:

• Point clouds: handled by the PointCloudOccupancyMapUpdater plugin.

• Depth images: handled by the DepthImageOccupancyMapUpdater plugin.

Note that you can add your own types of updaters as a plugin to the occupancy map monitor.

Octomap

The Occupancy map monitor uses an Octomap to maintain the occupancy map of the environment. The Octomap can actually encode probabilistic information about individual cells although this information is not currently used in MoveIt. The Octomap can directly be passed into FCL, the collision checking library that MoveIt uses.

Depth Image Occupancy Map Updater

The depth image occupancy map updater includes its own self-filter, i.e. it will remove visible parts of the robot from the depth map. It uses current information about the robot (the robot state) to carry out this operation.