4 ms·

Trees don't refract and reflect light.

• deleted 8y ago
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• jefft255 8y ago
  Of course they do. Airborne lidar usually works in the near infrared spectrum which is not absorbed by wood. It is however more absorbed by leaves which have a higher water content. My main point is: airborne lidar (which is what OP is referring to when talking about removing forests and keeping the ground) has multiple returns for one laser beam. Laser beams can have a radius of 1-2 meters or more when they hit the ground. By keeping only the lowest return in the z direction you most certainly have a ground point. It's not rocket science and interpreting ground lidar scans (velodyne and such) in bad weather is a much much more difficult problem.
  • mediaman 8y ago
    What would prevent using the same technique of only retaining the maximum Z direction return to tell the difference between a refracted rain drop and car bumper? Perhaps it is that the rain drop refracts the beam to all sorts of other objects which can make it difficult to tell which actually has the longest Z-distance return?
    • DoctorOetker 8y ago
      If I understand correctly the airborne LIDAR works in the timedomain and is much more expensive, while the LIDAR on automobiles is much more affordable but works in the frequency domain...
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