5

This is the actual scene:

enter image description here

This is the corresponding LiDAR scene:

enter image description here

The LiDAR data is from xyz file. The questions are:

  • Why are there no points for the dark squares on the checkerboard as well as the wall behind? Similarly, why are there no points for the floor but points for the "holes"?

  • Are xyz files preprocessed so that the undesired points are "removed"?

I'm new to LIDAR and point cloud processing so I'm seeking for help here.

  • 2
    if it was a raw scan it should have points everywhere, this one definitely seems processed. (except if the surface is 100% non reflective, so areas become holes) – elasticrash Aug 26 '15 at 12:07
  • what file formats are the raw scans and what are the tools available for processing the raw scans? I'm not being lazy for not searching but there's a myriad of different file types and lingo going around and I'm confused where to look first. – goh Aug 26 '15 at 12:10
  • 1
    it depends what sensor/method you used to record the point cloud, there are indeed a lot of different file types. strictly airborne lidars usually classify points so the formats are more complex then there are a huge range of point cloud scanners (handhelds, stationary, camera based, laser based) everyone using a different format. usually scanners are accompanied with their own software for processing raw scans. – elasticrash Aug 26 '15 at 12:16
  • ty elasticrash. very helpful to amateurs like me. – goh Aug 26 '15 at 12:23
  • 1
    Looks like the sensor's intensity trigger was not adjusted to compensate for the target material. – Jeffrey Evans Aug 26 '15 at 22:59
7

Dark areas = low reflectivity. Light areas = high reflectivity. My guess is the dark squares simply has not reflected light back to the transceiver and then you have no xyz data here.

For the floor my guess is that light is deflected away from aperture and not towards aperture, except for the holes. This depends of course of the sensor and the setup. In airborne lidar you may see the same effect when flying over lakes, just a small strip directly below the aircraft reflects light back to the sensor, else it is deflected (never reaches sensor and no xyz's).

XYZ files may or may not be pre-processed, directly from sensor they are not but some post-processing may take place before You have got your hands in the data.

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