[ros-users] Using IR distance sensors with costmap2d

[Eitan Marder-Eppstein]

Christian,

The reason that your IR sensors do not clear out of the costmap is that they
are at a different height than the laser and you've chosen (implicitly by
not setting the "map_type" parameter) to use a 3D voxel grid as your
underlying map structure. So, the laser will never clear out IR hits because
it lies strictly above them. Your IR sensors can clear out old hits, but
with only 9 points to raytrace to... its quite likely that many old hits
will not be seen through and thus are not safe to clear.

You have two options to clear these hits:

1) If you want your laser to be able to clear out hits from your IR sensors
once they are no longer observed, you could switch to the "map_type"
parameter to use "costmap": see
http://www.ros.org/wiki/costmap_2d#Map_type_parameters. This will use a 2D
representation of the world where everything is assumed to be on the same
plane.

2) You can continue using the 3D voxel grid and write your own sensor that
publishes a dense point cloud at the height of the IR sensors and is only
used for clearing. This sensor could publish the cloud at whatever rate you
want your IR hits to clear out.

Both of these options aren't strictly safe, consider the case where you see
an object with IR, move a little bit, clear that object out, don't see it
again, and hit it, but should probably help you do what you want.

Hope this helps,

Eitan

On Mon, Jul 26, 2010 at 6:34 AM, Christian Verbeek <
verbeek at servicerobotics.eu> wrote:

> Dear all,
>
> my robot is equipped with a laser rangefinder and 9 infrared distances
> sensors. The rangefinder is scanning at z=0.2 while the infrared sensors
> are scanning at z=0.05. So it absolutely makes sense to put the readings
> of the infrared sensors into the local costmap to avoid obstacles not
> seen by the rangefinder.
>
> I publish a point cloud with 9 points in it (the distances read from the
> 9 infrared sensors mapped to the base frame). The maximum range of the
> infrared sensors is 0.4m.
>
> My costmap_common_params.yaml look like this
>
> observation_sources: laser_scan_sensor ir_sensors
>
> laser_scan_sensor: {sensor_frame: laser_link, data_type: LaserScan,
> topic: scan, marking: true, clearing: true}
> ir_sensors: {sensor_frame: base_link, data_type: PointCloud, topic:
> ir_sensors, marking: true, clearing: true, obstacle_range: 0.4,
> raytrace_range: 0.4, observation_persistence: 0.0 }
>
> The obstacles detected by the infrared sensors are correctly put into
> the costmap. The problem is that the marker cells aren't cleared. So
> when I move around my robot the robot is surrounded by occupied cells
> and path planning does not work any more.
>
> What can I do?
>
> Regards
> Christian
>
>
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