[lasreader] Default point ordering ?

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Philippe Verley

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Nov 24, 2022, 8:17:14 AM11/24/22
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Hi there,

I am wondering whether there is any default/natural order guaranteed either by LAS specification or LASlib implementation when reading LAS points from a LAS/LAZ file ? 

I'm current;y developing https://www.amapvox.org software and we need reconstruct the LiDAR shot geometry. With LAS files, assuming there is no particular order when reading the points, I have to read all points and HEAP memory and order that list by GPS time. With large LAZ files it is becoming a hurdle. It would easier to read and process the points on the fly if I was sure there were read ordered by time (which seems to be true in practice over the tens of LAS/LAZ files I've tried but I cannot find any written evidence of this observation).

Cheers,
Philippe V.

michaelperdue99

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Nov 27, 2022, 4:18:55 AM11/27/22
to LAStools - efficient tools for LiDAR processing
Hi Philippe,

No, there is no natural order in the las specification or provided by LASlib. if you read the documentation for lassort or lasoptimize, you will see that points may be deliberately re-organized for inhanced performance.

In short, don't expect a la[sz] file to be sorted by time.

Cheers,

Mike

Philippe Verley

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Nov 29, 2022, 8:22:12 AM11/29/22
to LAStools - efficient tools for LiDAR processing
Thank you very much for the clarification!
Cheers,
Philippe
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