Questions about costmap_2D

asked 2016-12-12 12:21:38 -0600

sterlingm
380 ●25 ●38 ●39

Hi, I've been reading up on the costmap_2D package and I just can't seem to wrap my head about it. Here are a couple questions that hopefully someone on here can help me understand.

1) What is the difference between the OccupancyGrid published on /map by the Gmapping package and the OccupancyGrid published on /grid by the costmap_2D package? My understanding is that costmap_2D provides a way to update a map at real-time, but when I run the gmapping_demo.launch file in turtlebot_navigation, the map is also updated at real-time. So why is costmap_2D needed if the Gmapping package can build and update a map at real-time?

2) Where is the costmap_2D package actually run? The wiki makes me think that it is run in one of the navigation launch files, and that it is needed by the move_base node. However, when I run the amcl_demo.launch file, I do not see costmap_2D in the results of rosnode list. When I run rqt_graph with the amcl demo running, the only topics I see relevant to costmaps are published by move_base (they are /move_base/global_costmap/costmap, /move_base/global_costmap/costmap_updates, /move_base/local_costmap/costmap, and /move_base/local_costmap/costmap_updates), but they have no subscribers.

If anyone can help me understand, I would be very grateful.

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answered 2016-12-15 08:43:22 -0600

David Lu

10932 ●123 ●219 ●250 http://MetroRobots.com/

1) The model used by costmap_2d is much simpler/faster than gmapping. The costmap relies on localization for accurate position estimates, whereas gmapping keeps track of many more factors to publish a map and a position estimate. The costmap is primarily used when you have already built a static map and want to track your position within it using AMCL, while still performing dynamic obstacle avoidance.

2) Costmap_2d is usually not run by itself (although it can be). It is typically run from within move_base, with its results published as a convenience, not necessarily to be used by other nodes, thus explaining the lack of subscribers.

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