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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. The slam_gmapping node will attempt to transform each incoming scan into the odom (odometry) tf frame. See the "Required tf transforms" 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 sensor_msgs/LaserScan messages and builds a map (nav_msgs/OccupancyGrid). The map can be retrieved via a ROS topic or service.

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

Published 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

~entropy (std_msgs/Float64)

• Estimate of the entropy of the distribution over the robot's pose (a higher value indicates greater uncertainty). New in 1.1.0.

Services

dynamic_map (nav_msgs/GetMap)

• Call this service to get the map data

Parameters

~inverted_laser (string, default: "false")

• (REMOVED in 1.1.1; transform data is used instead) Is the laser right side up (scans are ordered CCW), or upside down (scans are ordered CW)?

~throttle_scans (int, default: 1)

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

~base_frame (string, default: "base_link")

• The frame attached to the mobile base.

~map_frame (string, default: "map")

• The frame attached to the map.

~odom_frame (string, default: "odom")

• The frame attached to the odometry system.

~map_update_interval (float, 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 (float, default: 80.0)

• The maximum usable range of the laser. A beam is cropped to this value.

~sigma (float, default: 0.05)

• The sigma used by the greedy endpoint matching

~kernelSize (int, default: 1)

• The kernel in which to look for a correspondence

~lstep (float, default: 0.05)

• The optimization step in translation

~astep (float, default: 0.05)

• The optimization step in rotation

~iterations (int, default: 5)

• The number of iterations of the scanmatcher

~lsigma (float, default: 0.075)

• The sigma of a beam used for likelihood computation

~ogain (float, default: 3.0)

• Gain to be used while evaluating the likelihood, for smoothing the resampling effects

~lskip (int, default: 0)

• Number of beams to skip in each scan.

~srr (float, default: 0.1)

• Odometry error in translation as a function of translation (rho/rho)

~srt (float, default: 0.2)

• Odometry error in translation as a function of rotation (rho/theta)

~str (float, default: 0.1)

• Odometry error in rotation as a function of translation (theta/rho)

~stt (float, default: 0.2)

• Odometry error in rotation as a function of rotation (theta/theta)

~linearUpdate (float, default: 1.0)

• Process a scan each time the robot translates this far

~angularUpdate (float, default: 0.5)

• Process a scan each time the robot rotates this far

~temporalUpdate (float, default: -1.0)

• Process a scan if the last scan proccessed is older than the update time in seconds. A value less than zero will turn time based updates off.

~resampleThreshold (float, default: 0.5)

• The Neff based resampling threshold

~particles (int, default: 30)

• Number of particles in the filter

~xmin (float, default: -100.0)

• Initial map size

~ymin (float, default: -100.0)

• Initial map size

~xmax (float, default: 100.0)

• Initial map size

~ymax (float, default: 100.0)

• Initial map size

~delta (float, default: 0.05)

• Processing parameters (resolution of the map)

~llsamplerange (float, default: 0.01)

• Translational sampling range for the likelihood

~llsamplestep (float, default: 0.01)

• Translational sampling step for the likelihood

~lasamplerange (float, default: 0.005)

• Angular sampling range for the likelihood

~lasamplestep (float, default: 0.005)

• Angular sampling step for the likelihood

~transform_publish_period (float, default: 0.05)

• How long (in seconds) between transform publications.

~occ_thresh (float, default: 0.25)

• Threshold on gmapping's occupancy values. Cells with greater occupancy are considered occupied (i.e., set to 100 in the resulting sensor_msgs/LaserScan). New in 1.1.0.

~maxRange (float)

• The maximum range of the sensor. If regions with no obstacles within the range of the sensor should appear as free space in the map, set maxUrange < maximum range of the real sensor <= maxRange.

Required tf Transforms

<the frame attached to incoming scans> → base_link

• usually a fixed value, broadcast periodically by a robot_state_publisher, or a tf static_transform_publisher.

base_link → odom

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

Provided tf Transforms

map → odom

• the current estimate of the robot's pose within the map frame