I have a very small and cheap robot and I wanted to mount a 2D LiDAR on a bottom of it (3cm above the ground). It seems to be great as during the mapping the lidar will detect even small elevations from the ground.

But what happens when a chair will be in front of this LiDAR? I guess it will see only its legs due to a limited optical window (as it is 2D). How can I cope with that? So my robot will not try to go under the chair.

This is the LiDAR: LINK

  • $\begingroup$ How can I cope with that? .... how to cope with what? ..... why would you need to keep the robot from going under the chair? ...... you have not clearly described your project, otherwise these questions would not be necessary $\endgroup$ – jsotola Nov 23 '18 at 0:40
  • $\begingroup$ hint: what would you use to see around a corner? $\endgroup$ – jsotola Nov 23 '18 at 7:53

The answer by @nathangeorge1 is valid for the case of not hitting the legs of the chair.

However, you are faced with limited sensor input. This is the case for most robots, even people need to turn their heads to see what is behind them. Either you need to mount more sensors or you may actuate the lidar. You can see an example of an actuated lidar on the PR2 robot platform under its chin in this video.

You could also use a depth camera like the Realsense cameras from Intel or the Structure cameras from Occipital. These cameras will give you a limited field-of-view compared to the LIDAR, but will provide depth information also above the robot.

A cheaper solution is to use ultrasonic sensors. Mounting them pointing upwards will give the robot a sense of obstacles above it. Alternatively the IR based range finders from Sharp, models GP2Y0xxxxxxx, does almost the same job.


The LiDAR won't go under the chair if your mapper inflates the occupied space created by the legs of the chair; ROS's move_base package does this automatically.

The problem with this approach is then the robot will have a harder time going through narrow corridors, doors, or hallways.

  • $\begingroup$ What happens if you want to stop the robot from driving under a bed? Inflate everything by one meter? $\endgroup$ – FooTheBar Nov 29 '18 at 14:23
  • 2
    $\begingroup$ the question was about 2D lidar solutions for chairs, not beds or new sensors $\endgroup$ – Void Nov 29 '18 at 15:23
  • $\begingroup$ No, the question is about how to detect objects that are outside of the measurement plane and a chair is only one example. $\endgroup$ – FooTheBar Nov 29 '18 at 16:56

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