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how can I build probability maps with gmapping

asked 2012-06-03 22:15:41 -0600

igoliao gravatar image

updated 2012-06-03 22:19:59 -0600

I want build probability maps, but I find that gmapping can only generate maps with 3 values (unknown, free and obstacle). How can gmapping work with probablility maps. Thank you. Further, I change source code, but it doesn't work too.

the code I changed is below: if(occ < 0)[MAP_IDX(, x, y)] = -1; else[MAP_IDX(, x, y)] = (int)round(occ*100.0);

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answered 2012-06-04 00:55:07 -0600

updated 2012-06-04 01:02:46 -0600

It's not gmapping that is using only three discrete values, but the nav_msgs/OccupancyGrid.msg message format. Internally, gmapping uses probabilistic cell values, but in the slam_gmapping.cpp source, starting in line 631, those are converted to above linked message format like so:

for(int y=0; y < smap.getMapSizeY(); y++)
  /// @todo Sort out the unknown vs. free vs. obstacle thresholding
  GMapping::IntPoint p(x, y);
  double occ=smap.cell(p);
  assert(occ <= 1.0);
  if(occ < 0)[MAP_IDX(, x, y)] = -1;
  else if(occ > occ_thresh_)
    //[MAP_IDX(, x, y)] = (int)round(occ*100.0);[MAP_IDX(, x, y)] = 100;
  else[MAP_IDX(, x, y)] = 0;

Haven't played around with the code, but the occ variable should hold the probability of occupancy.

See also this question/answer about visualization in rviz.

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Hi Stefan, I guess it is an update after a long time! When I was trying to work on your suggestion and tried assigning the occ value directly to the map data and publish it I find the same -1,0,100 as the values and cant access the probability. Do you have some more input about this?

Thanks in advance

A_Hari gravatar image A_Hari  ( 2019-05-10 10:00:53 -0600 )edit

answered 2012-06-03 23:43:06 -0600

dornhege gravatar image

I would be very surprised if gmapping only outputs three values. You should have occupancies in the maps. Maybe you are doing something wrong in interpreting the raw data.

Also, the fact that you changed some line of code somewhere and "it doesn't work", doesn't encourage someone to properly help you.

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Asked: 2012-06-03 22:15:41 -0600

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Last updated: Jun 04 '12