Point return numbers are all 0

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Pierre Abbat

Jul 15, 2019, 2:22:53 AM7/15/19
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I'm writing a program to process point clouds. Initially it read only PLY
files, then I added code to read LAS files. The first LAS file I got is
DH178.las, a laser scan of a piece of West Virginia terrain. It's a LAS 1.4
file; the point numbers are 13051948, 9081971, 3177106, 699687, 86863, 6062,
255, and 4, which add up correctly. As it has sixth and seventh return points,
the legacy numbers are zero.

A surveyor named Pat gave me a photogrammetric LAS file of a parking lot. It's
a LAS 1.2 file; I added the code to read it. The number of points is 250024,
and the number of first-return points (which is meaningless, since it's
photogrammetric) is also 250024. That checks, so the program read 250024

Another surveyor named Cliff gave me another LAS 1.2 file. I ran my program on
it and it said "No point cloud found". I looked at it in a hex editor. There
are 22850601 points, but all the numbers of points by return are 0, so my
program threw out the legacy numbers as unverified. The eight-byte point
numbers don't exist, since this isn't LAS 1.4. Is this valid? Should I output
a warning or error if this happens?

Jews use a lunisolar calendar; Muslims use a solely lunar calendar.

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