Applying geoid to DEM appears to have no effect

[colin.spexigeo]

Hello again,

As one of the final steps of our processing pipeline, I need to apply a geoid to adjust the DEM elevations (current DEM values are based on WGS84 ellipsoidal elevation).

The geoid I'm using is CGG2013.

I'm attempting to programmatically accomplish the addition of a new CRS with geoid as laid out in this tutorial. Here's how I'm going about it:

Code: [Select]

geoid_path = os.path.join(geoids_directory, 'EPSG 4269', 'CGG2013.tif')
crs = Metashape.CoordinateSystem('EPSG::4269')  # NAD83
crs.addGeoid(geoid_path)
self.chunk.buildDem(projection=crs)
The DEM end sup in NAD83, however, it seems to have had no effect on the resultant elevations coming back in the DEM. Am I missing something here?

Thank you for your time,
Colin

[Alexey Pasumansky]

Hello Colin,

addGeoid functions just specifies the path to the undulation grid, it doesn't modify the coordinate system definition.

You should define the coordinate system with vertical datum either via EPSG code or using WKT definition (as string or external PRJ file).

What is the target coordinate system you are interested in? Are you sure that the XY coordinates should be defined as degrees and you are not looking for some projected system on NAD83?