map_matcher

map_matcher is a ros node which matches a source map to a reference map.

Example - Using Map Matcher to Localize

• Create a map with gmapping. When done, save map.yaml and map.pgm to ~/maps/ .
• run gmapping again. It should be publishing a map to the topic /map (nav_msgs/OccupancyGrid)
• While gmapping is running, launch map_matcher (both client and server will be run):
  $roslaunch map_matcher map_matcher.launch

After successful map matching, both maps should be visible in rviz, and transforms between the two map frames will be published to tf.

Using the map_matcher server separately

The map_matcher_client node is provided as an example. However, you are free to call the services advertised by the server directly from within your code, according to the map_matcher_server interface.

map_matcher_server node

The map_matcher_server node by itself exposes two services:

• set_reference_map (map_matcher.srv.SetReferenceMap)
• match_to_reference (map_matcher.srv.MatchToReference)

set_reference_map: expects a map in the format nav_msgs/OccupancyGrid.
match_to_reference: runs the branch and bound matching algorithm.
expects a map in the format nav_msgs/OccupancyGrid
returns the match information (success, pose, angle, score)

Both maps should have similar resolutions for the matching algorithm to succeed.

An example launch file for running the map_matcher_server standalone can be found in launch/map_matcher_server.launch

Parameters

map_matcher_client parameters

• acceptance_ratio (float, default 0.5) : Proportion of occupied points in the source map that must match to an occupied point in the reference map in order for the match to be accepted. should be a value between 0 and 1. Higher is stricter (at 1, all points must match) and faster. A good default value is 0.5
• rotation_downsampling (int, default 1) : multiplies the default angular resolution, increasing this value leads to less accurate results but faster execution. should be 1 or larger than 1.
• hits_sample_threshold (int, default 0) : if a value n other than 0, n occupied points in the source map will be sampled randomly to reduce computation. should be 0 or a positive integer.

map_matcher_server parameters

The above parameters are passed at runtime from client to server with each map request via the MatchToReference service request.