I am new to LiDAR and have never been a part of the LiDAR data pre-processing stage and hence, this question. I have two LiDAR point clouds (.las files) of a densely forested area that were captured from two different sensors (A and B). Both of the point clouds have an offset due to incorrect GPS calibration during time of capture.

The only hint I have to correctly georeference the point clouds is with a known location of a carbon flux tower [let's say at (X,Y)m].

Would I be heading in the right direction to write a python script that could just correct the offset in the point clouds to match with (x,y)?

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  • The simplest way is to export las files to multipoint and use spatial adjustment. This is ArcGIS solution though – FelixIP Mar 1 '16 at 4:59
  • @FelixIP thanks for your suggestion. Tried the method but didn't work..The point cloud is so dense that it doesn't let me match a single point to the reference point. – Amritha Hariharan Mar 1 '16 at 7:07
  • Arcgis goes mad when need to snap to big sets. Just fool it. Extract small subsets and work on them, but turn the biggie off. It will help to construct displacement links, i.e. table needed for adjustment – FelixIP Mar 1 '16 at 8:30
  • If this is about coordinate shift, i.e. 1 link, convert multipoints to single and use technique described here gis.stackexchange.com/questions/159206/… – FelixIP Mar 1 '16 at 8:33

I assume both point clouds have the same coordinate reference system.

Then, if you know the actual tower location in the field, and also know its location in the point clouds; then, yes, one solution would be to offset the .las files based on the common reference point (the tower).

It is possible to shift the x, y and z coordinates with LAStools, las2las tool plus its argument offset. See the example below:

las2las -i forest.las -o shifted_forest.las --offset:-1050,-503,0

It will shift the x coordinates to west by 1050 distance units, and the y coordinates to south by 503 distance units. In this case, elevations will not be altered.

It is important though, that you validate the new position of your points, by comparing one point cloud with another, and if possible, by trying to match other known locations in the LiDAR scene with reference points in the field, besides the tower.

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