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I'm really a newbie and this task seems over my head. Suppose you have one cloud from LiDAR (a LAS file) with coordinates in WGS84 and another cloud, obtained from structure-from-motion, in ECEF. They represent a 100 mt long street and one (say the first) have to be used as ground truth for a statistical comparison.

My intention is to use the Python library laspy to extract the coordinates of the points and pyproj (the Python interface to PROJ) to convert from WGS84 to ECEF. I'm especially worried about losing accuracy when doing this conversion. One example of the coordinates I have in my LAS file (1.2 version, point data record 1, proj=latlon) is:

((-8495308, 1344287, 84460, 100, 9, 1, 0, 0, 1576, 1.52689438e+08),)

with scale [1e-08, 1e-08, 0.0001]

and offset [30.40828783662081, 59.9284293900385, 20.370796515028587].

In order to convert to ECEF, I have to apply both scale and offset to obtain actual values of lon, lat and elevation. Am I losing accuracy doing these operations? Is there any alternative?

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  • What accuracy do you aim for?
    – bugmenot123
    Jun 22, 2020 at 6:24
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    Hello bugmenot123, actually i cannot answer your question precisely, i only wanted to have an idea of the consequences of the transformation. The LAS point cloud will be the reference for a comparison with the same cloud reconstructed by photogrammetry, so it has to be very precise (order of mm I guess). In the meanwhile i accomplished to do the conversion from WGS84 to ECEF with las2las in LAStools.
    – Fabrizio Pellegrini
    Jun 24, 2020 at 9:55

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