Monday, May 14, 2018

Use PDAL to apply a vertical datum geoid correction to a LAS file

PDAL can be used to apply a vertical datum correction to LAS files, e.g. to convert LiDAR data in ellipsoidal heights to mean sea level using a geoid such as the EGM2008. PDAL uses geoids in gtx format and can be downloaded from http://download.osgeo.org/proj/vdatum/

The following steps show how to perform a vertical datum correction with the reprojection filter of PDAL:
  1. Optional. Download an appropriate geoid file e.g. egm08_25.gtx for EGM2008 from http://download.osgeo.org/proj/vdatum/ and place it in a folder e.g. D:\Temp\PDAL\
  2. Open up the OSGeo4W Shell.
  3. In the Command Prompt, type in the following command:

    D:\> pdal translate -i input.las -o output.laz reprojection --filters.reprojection.in_srs="EPSG:32610+4326" --filters.reprojection.out_srs="+init=EPSG:32610 +geoidgrids=D:/Temp/PDAL/egm08_25.gtx" --writers.las.compression="true" --writers.las.a_srs="EPSG:32610+3855" -v 4

    where
    --filters.reprojection.in_srs specifies the source coordinate reference system EPSG:32610 or UTM 10 North  and the source vertical datum of EPSG:4326 which is the WGS84 Ellipsoid

    --filters.reprojection.out_srs specifies the destination coordinate reference system EPSG:32610 (the same as the input) and the EGM2008 grid file to apply

    --writers.las.a_srs tells PDAL to write the destination coordinate reference system of EPSG:32610 and vertical datum EPSG:3855 (which is the EGM2008 datum) to the output file.


  4. Press RETURN.

    Processing messages appear. The input las file is reprojected to the EGM2008 vertical datum.

  5. Optional. Overlay the input and output LAS files in a viewer and observe the vertical offset in a profile as shown below.

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