LIDAR produces "phantom walls"
Hello,
We have a SICK LMS100 LIDAR attached to the front of our mobile robot and we have been using it for several years. We suddenly started noticing "phantom walls" appearing in the laser scan when viewed in RViz. You can see a video of the phenomenon here. The small yellow dots in the video are produced by a rotating LIDAR on the head of the robot and these dots line up correctly with the surrounding walls and other obstacles. The larger colored dots are the LMS LIDAR points shown in intensity view. Near the beginning of the video you can see how the LMS points line up with the yellow dots along a wall at the far right. As the robot backs up, the LMS readings "pull off" the real wall but continue to produce a phantom wall that moves with the robot.
We have observed the same phenomenon whenever there is a symmetrical gap that the robot is facing and the phantom wall is always positioned at roughly the same distance from the robot.
Can anyone explain what is going on here? Is the LMS faulty at the hardware level? Or is this some kind of reflection problem that we can filter?
Thanks! patrick
Is the lidar getting tilted and is pointing at the floor in those instances? Try putting something on the floor with some height but that should always lie beneath the scan plane but will be noticeable if the robot or sensor angles down.
Maybe the lidar lens is dirty or the power input to the lidar is drooping? P.S. I recognized your name on the Youtube channel, I read ROS by Example a while back, excellent book!
I agree. I use the book and recommend it to others.
@lucasw - Thanks for the suggestion but the scanner is definitely not tilting down and data further away than the "phantom" wall shows up OK.
@Airuno2L - Wouldn't a dirty lens cause a permanent reading rather than the odd intermittent reading we get? Also, we can reproduce the phantom wall effect at certain locations time after time so I don't think it is a power fluctuation which presumably would occur at other locations as well.
P.S. Thanks for the book recommendation. :)
Can you share a bag of what is in that video on botbags or marvhub?
I'll post a bag file on Monday assuming we haven't figured out the issue by then.