1

I have a LiDAR .laz file with points from Toulouse (France). I convert this file to a .las file using LAStools's las2las function. Then, using lasinfo on this .las file gives me some information, including:

GeoKeyDirectoryTag version 1.1.0 number of keys 3
  key 1024 tiff_tag_location 0 count 1 value_offset 2 - GTModelTypeGeoKey: ModelTypeGeographic
  key 2048 tiff_tag_location 0 count 1 value_offset 4326 - GeographicTypeGeoKey: GCS_WGS_84
  key 4099 tiff_tag_location 0 count 1 value_offset 9001 - VerticalUnitsGeoKey: Linear_Meter

So, I assume that my data is in the WGS84 format.

Regarding points, I have this information using lasinfo on my .las file:

scale factor x y z:         0.001 0.001 0.001
offset x y z:               1574926.999698425875977 3157519.458761402405798 142.690597958476445
min x y z:                  1574775.710 3157384.005 125.497
max x y z:                  1574981.625 3157614.866 226.186

Looking, for exemple, at the minimum point which should be located in Toulouse: (1574775.710, 3157384.005) and following the .las documentation, my real point is :

Xcoordinate = (Xrecord * Xscale) + Xoffset
Xcoordinate = (1574775.710 * 0.001) + 1574926.999698425875977 = 1576501.774698425875977
Ycoordinate = (3157384.005 * 0.001) + 3157519.458761402405798 = 3160676.842761402405798

However, as I saw on many sources, WGS_84 should be between [-90, 90] and [-180, 180], right ?

I saw this question on the forum that may be related to my problem, but even playing with the 3second-->100m that he talks about, I can't find any way to go from my data point (1574775.710, 3157384.005) to the (43.603266, 1.442261) latitude/longitude point that Google Maps gives me for Toulouse in France.

Capitole, Toulouse, France

1

I finally managed to solve my problem.

The weird thing is that the coordinates inside my .laz file weren't projected using WGS_84 but CC44. I still don't know why it was written GCS_WGS_84 in the lasinfo return.

An other thing that mistook me was that scaling and adding the offset gave me a less precise result than taking the raw min coordinate given by lasinfo. That's because those min and max coordinates are already scaled and translated when given by lasinfo.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.