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As far as I know, gmapping maintains occupancy values internally. However, the ROS wrapper thresholds them into binary free/occupied values.

Take a look at this file:

slam_gmapping.cpp

Starting at line 625:

for(int x=0; x < smap.getMapSizeX(); x++)
{
  for(int y=0; y < smap.getMapSizeY(); y++)
  {
    GMapping::IntPoint p(x, y);
    double occ=smap.cell(p);
    assert(occ <= 1.0);
    if(occ < 0)
      map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = -1;
    else if(occ > occ_thresh_)
    {
      //map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = (int)round(occ*100.0);
      map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = 100;
    }
    else
      map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = 0;
  }
}

The default value for occ_thresh_ is 0.25. It appears that if you want the occupancy values, you can simply revert the line which was commented out, and change the code to:

map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = (int)round(occ*100.0);
//map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = 100;

I have created a ticket here.

As far as I know, gmapping maintains occupancy values internally. However, the ROS wrapper thresholds them into binary free/occupied values.

Take a look at this file:

slam_gmapping.cpp

Starting at line 625:

for(int x=0; x < smap.getMapSizeX(); x++)
{
  for(int y=0; y < smap.getMapSizeY(); y++)
  {
    GMapping::IntPoint p(x, y);
    double occ=smap.cell(p);
    assert(occ <= 1.0);
    if(occ < 0)
      map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = -1;
    else if(occ > occ_thresh_)
    {
      //map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = (int)round(occ*100.0);
      map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = 100;
    }
    else
      map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = 0;
  }
}

The default value for occ_thresh_ is 0.25. It appears that if you want the occupancy values, you can simply revert the line which was commented out, and change the code to:

map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = (int)round(occ*100.0);
//map_.map.data[MAP_IDX(map_.map.info.width, x, y)] = 100;

I have created a ticket here.