Laser scanner - filter out hits on the robot itself

[kri...@gmail.com]

Patrick,

On your hardware page [1] you explain that you mounted your Hokuyo laser scanner at the front bottom of your robot, just in front of the wheels, to keep it out of harm's way.

Makes sense to me, but I was wondering how you deal with this "obstructed" position in your ROS code.

Do you filter out hits on the robot itself, and if yes, how?
Do you use the ROS laser_filters package [2]? Or is this somehow taken care of automatically in your URDF model of the robot?

Thanks,

Kristof

[1] http://www.pirobot.org/blog/0024/
[2] http://wiki.ros.org/laser_filters

[kri...@gmail.com]

Just after having posted this question, I found a very relevant ROS Answer here: http://answers.ros.org/question/10821/filter-robot-out-of-laser-scan/

It describes a package that filter out the robot based on the URDF description - pretty neat!

It also states that on the Turtlebot, the turtlebot_laser node simply filters out all points within the radius of the base - which is elegant as well, but obviously only works when the laser is placed in the center of the base.

Still would be interested to know how this is done on Pi Robot :)

Thanks,

Kristof

[KM6VV]

Angle of LiDAR is something like 240 degrees, so with careful
positioning, one can avoid getting the wheels in the view.

Alan KM6VV

[Kristof Robot]

Alan,

Indeed, Hokuyo's URG-04LX-UG01 [1] has a scanning range of 240
degrees, that explains it.

Thanks!

Kristof

[1] http://www.robotshop.com/ca/en/hokuyo-urg-04lx-ug01-scanning-laser-rangefinder.html

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[Patrick Goebel]

Hi Kristof,

The approach I took was to set the scanning angle for the laser in the launch file:

<launch>
  <!-- Run the Hokuyo laser scanner node -->
  <node name="hokuyo" pkg="hokuyo_node" type="hokuyo_node">
    <param name="port" value="/dev/laser" />
    <param name="min_ang" value="-1.7" />
    <param name="max_ang" value="1.7" />
    <param name="hokuyo_node/calibrate_time" value="true" />
    <param name="frame_id" value="/base_laser" />
  </node>
</launch>

Note how I set the max and min angles to +- 1.7 radians which is about 97 degrees to either side.  I chose these angles so that the laser would just miss the two closest standoffs.

--patrick

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