Goals and Navigation in dynamic maps using GMapping

asked 2011-05-11 06:51:02 -0600

Pablo Hevia-Koch
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Hello Everyone,

Lately I've been experimenting on using the navigation stack without the mapserver, and using GMapping for the generation of a map via Online SLAM, with very good results (although sometimes a little CPU intensive).

I was wondering how could I refer to a point the robot has visited in the past, when the map is continually changing. Here is an example of my question:

Suppose I am giving my robot a tour of the office (he doesn't have a prior knowledge of its environment). While we tour, at certain positions I will "mark" some place, for example, "this is Ben's desk". After the tour, I would like to be able to tell the robot to go to Ben's desk.

I am not sure how I could manage to do that if the map is continually changing, in size, orientation, etc. Is there a way that doesn't rely exclusively on odometry?

Thanks in advance. All ideas are welcome :)

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answered 2011-05-11 07:15:30 -0600

dornhege

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Well, in theory the map should not be changing, just growing in terms of adding information. So, if you mark your current location in the /map frame, then this should later also be the same position to go back to.

If the maps you are producing look OK, this should be sufficient. Otherwise you need a better SLAM solution or remember the environment and use some global matching procedure to find the spot.

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Are you sure about this? I've seen maps change in the sense of "deformation" when closing loops, and similar things.

Pablo Hevia-Koch ( 2011-05-11 07:16:54 -0600 )edit

That what the "in theory" was for. It can happen that the map deforms to correct accumulated errors. The only real solution is: better SLAM algorithm/input quality or to use some kind of place recognition. E.g. with graph-based SLAM you could remember the current node.

dornhege ( 2011-05-12 05:28:15 -0600 )edit

Thank you very much for your advice =). I'll give it a shot

Pablo Hevia-Koch ( 2011-05-12 06:29:10 -0600 )edit

Have you made any achievements? I need to do the same. Or are there any packages to mark positions?

felix k ( 2011-09-14 02:11:33 -0600 )edit

@dornhege How do yo tag a position in the /map??? Ive looked for this answer but was unable to find it. Thanks

ctguell ( 2013-09-12 10:10:52 -0600 )edit

Just transform your position from its odom frame (or where it is originated from) to the map frame using `tf` and store it in a list of positions as wanted.

felix k ( 2013-09-15 22:59:52 -0600 )edit

@felix_k thanks but could you explain how to store that position so later I can see it in rviz for example?? Should i listen to /map and then publish it with a new topic?? I understand the idea but dont know how to make it work, i would really appreciate your help, thanks

ctguell ( 2013-09-24 07:34:22 -0600 )edit

I've had written a tool that stores positions and can give them to `move_base` later, storing just the geometry_msg/Pose objects used in all messages in a list: [position_memo.py](https://github.com/felix-kolbe/uashh-rvl-ros-pkg/blob/master/position_memo/src/position_memo.py)

felix k ( 2013-09-24 23:04:25 -0600 )edit

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answered 2011-05-11 08:31:01 -0600

Dimitar Simeonov
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I pretty much agree with dornhedge that /map shouldn't be changing too much.

Another, pretty ad-hoc solution would be to remember the local environment when a position is tagged and then to do some kind of nearest neighbor search in your updated map, with a (possibly gaussian) prior over the odometry estimate for Ben's desk.

But that may be too much hassle and/or computation to implement/run.

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