Explore possibilities for adding cLoD to las files

[vanlankveldthijs]

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Also check whether PoTree can load these las/laz files and whether we need to 'hyjack' other known attributes for cLoD

[bmmeijers]

Las v.1.4 gives 'extra_bytes' for user defined attributes per point. las-rs does not support it, laspy and pdal do

• ASPRS spec: http://www.asprs.org/wp-content/uploads/2019/07/LAS_1_4_r15.pdf#subsection.0.4.3 (section 4.3, Table 24, page 43)

The various libraries that give info about it:

• PDAL: https://pdal.io/stages/writers.las.html#options > extra_dims : PDAL writes an extra bytes VLR (User ID: LASF_Spec, Record ID: 4) when extra dims are written. The VLR describes the extra dimensions specified by this option. Note that reading of this VLR is only specified for LAS version 1.4, though some systems will honor it for earlier file formats. The LAS reader requires the option use_eb_vlr in order to read the extra bytes VLR for files written with 1.1 - 1.3 LAS format.
• laspy: https://pythonhosted.org/laspy/tut_part_3.html#new-format-features-las-versions-1-3-and-1-4
• las-rs: https://github.com/gadomski/las-rs/issues/12 asks for implementing extra bytes (I think this is asking for a more structured approach to deal with the extra bytes at the API level)