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External Documentation

This is mostly a third party package; the underlying GMapping library is externally documented. Look there for details on many of the parameters listed below.

Hardware Requirements

To use slam_gmapping, you need a mobile robot that provides odometry data and is equipped with a horizontally-mounted, fixed, laser range-finder. slam_gmapping will attempt to transform each incoming scan into the odometry frame. See below for more on required transforms.

Example

To make a map from a robot with a laser publishing scans on the base_scan topic:

rosrun gmapping slam_gmapping scan:=base_scan

Nodes

slam_gmapping

The slam_gmapping node takes in laser scans and builds a map. The map can be retrieved via topic or service.

ROS API

Subscribed topics

• tf (tf/tfMessage) : Transforms necessary to relate frames for laser, base, and odometry (see below)

• scan (sensor_msgs/LaserScan) : Laser scans to create the map from

Advertised topics

• map_metadata (nav_msgs/MapMetaData) : Get the map data from this topic, which is latched, and updated periodically.

• map (nav_msgs/OccupancyGrid) : Get the map data from this topic, which is latched, and updated periodically

Advertised services

• dynamic_map (nav_msgs/GetMap) : Call this service to get the map data

Parameters used

• ~inverted_laser (default: false) : Is the laser right side up (scans are ordered CCW), or upside down (scans are ordered CW)?

• ~throttle_scans (default: 1) : Process 1 out of every this many scans (set it to a higher number to skip more scans)

• ~base_frame (default: "base_link") : The frame attached to the mobile base.

• ~map_frame (default: "map") : The frame attached to the map.

• ~odom_frame (default: "odom") : The frame attached to the odometry system.

• ~map_update_interval (default: 5.0) : How long (in seconds) between updates to the map. Lowering this number updates the occupancy grid more often, at the expense of greater computational load.

• ~maxUrange (default: 80.0) : The maximum usable range of the laser. A beam is cropped to this value.

• ~sigma (default: 0.05) : The sigma used by the greedy endpoint matching

• ~kernelSize (default: 1) : The kernel in which to look for a correspondence

• ~lstep (default: 0.05) : The optimization step in translation

• ~astep (default: 0.05) : The optimization step in rotation

• ~iterations (default: 5) : The number of iterations of the scanmatcher

• ~lsigma (default: 0.075) : The sigma of a beam used for likelihood computation

• ~ogain (default: 3.0) : Obstacle gain (?)

• ~lskip (default: 0) : Number of beams to skip in each scan.

• ~srr (default: 0.1) : Odometry error in translation as a function of translation (rho/rho)

• ~srt (default: 0.2) : Odometry error in translation as a function of rotation (rho/theta)

• ~str (default: 0.1) : Odometry error in rotation as a function of translation (theta/rho)

• ~stt (default: 0.2) : Odometry error in rotation as a function of rotation (theta/theta)

• `~linearUpdate (default: 1.0) : Process a scan each time the robot translates this far

• ~angularUpdate (default: 0.5) : Process a scan each time the robot rotates this far

• ~resampleThreshold (default: 0.5) : The neff based resampling threshold (?)

• ~particles (default: 30) : Number of particles in the filter

• ~xmin (default: -100.0) : Initial map size

• ~ymin (default: -100.0) : Initial map size

• ~xmax (default: 100.0) : Initial map size

• ~ymax (default: 100.0) : Initial map size

• ~delta (default: 0.05) : Processing parameters (resolution of the map)

• ~llsamplerange (default: 0.01) : Translational sampling range for the likelihood

• ~llsamplestep (default: 0.01) : Translational sampling range for the likelihood

• ~lasamplerange (default: 0.005) : Angular sampling range for the likelihood

• ~lasamplestep (default: 0.005) : Angular sampling step for the likelihood

tf API

Required transforms

• <the frame attached to incoming scans> → base_link : usually a fixed value, broadcast periodically by mechanism_control, or a tf/transform_sender

• base_link → odom : usually provided by the odometry system (e.g., the driver for the mobile base)

Provided transforms

• map → odom