Save 2D map

[Hunter L. Allen]

Hey all,

I was wondering what I'm doing wrong here: I'm just trying to save a 2D map, but the output map is rather strange.

I just ran a simple

```

rosrun map_server map_saver

```

to produce this. What's odd to me is the lack of occupancy lines -- the walls are not being registered somehow. Am I doing something incorrectly?

Thanks,

--Hunter

[Holger Rapp]

​Does the /map look good in rViz? Do the /submaps look good? Could you attach a screenshot?​

My initial hunch is that map_saver does some sort of discretization at sub-optimal values.

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[dgrie...@6river.com]

We ran into this problem as well.  The map_saver node discretizes the map such that 100 is lethal, 0 is free, and anything else is unknown space.  Because Cartographer outputs the probability from 0-100, only things that are 100% likely to be an obstacle are saved as lethal obstacles by map_saver.  Our solution was to modify map_saver to take ranges for the values, i.e. 0-20 is free, 21-64 is unknown, and 65-100 is lethal.  We have not yet pushed a PR to ros-navigation for this change.

Cheers,

Dan

On Monday, July 31, 2017 at 5:10:02 AM UTC-4, Holger Rapp wrote:

​Does the /map look good in rViz? Do the /submaps look good? Could you attach a screenshot?​

My initial hunch is that map_saver does some sort of discretization at sub-optimal values.

On Fri, Jul 28, 2017 at 10:48 PM, Hunter L. Allen <hun...@osrfoundation.org> wrote:

Hey all,

I was wondering what I'm doing wrong here: I'm just trying to save a 2D map, but the output map is rather strange.

I just ran a simple

```

rosrun map_server map_saver

```

to produce this. What's odd to me is the lack of occupancy lines -- the walls are not being registered somehow. Am I doing something incorrectly?

Thanks,

--Hunter

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[Hunter L. Allen]

On Monday, July 31, 2017 at 6:31:50 AM UTC-7, dgrie...@6river.com wrote:

We ran into this problem as well.  The map_saver node discretizes the map such that 100 is lethal, 0 is free, and anything else is unknown space.  Because Cartographer outputs the probability from 0-100, only things that are 100% likely to be an obstacle are saved as lethal obstacles by map_saver.  Our solution was to modify map_saver to take ranges for the values, i.e. 0-20 is free, 21-64 is unknown, and 65-100 is lethal.  We have not yet pushed a PR to ros-navigation for this change.

You were very right! That's rather strange, as the comments are even there with the desired bounds. I guess this comes from the fact that GMapping itself rounds up, so it made sense for the map server to as well. 

I suppose it would be best to update the output yaml so that the occupancy is reflective of the input occupancy.

A PR upstream would almost certainly be welcome.

Cheers,

-Hunter

[Guillaume Doisy]

I am having the same issue. Is there currently a way to save a 2D map generated by cartographer?

[Guillaume Doisy]

Thanks a lot!

"I've PR'd the changes into the navigation stack.

https://github.com/ros-planning/navigation/pull/613

You can checkout that branch for a temporary fix, and, otherwise, you can wait for the next nav stack release (assuming that gets merged before then)."

[Damon Kohler]

We don't recommend saving the map via map_saver due to the issues you all described. Instead, this should be implemented in the asset writer pipeline. This regression/feature is being tracked in https://github.com/googlecartographer/cartographer_ros/issues/475

Cheers,

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Cheers,

-Hunter

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