Hi @Alexander_Johannesen, thanks for your observations. I wanted to clarify one thing:
One would think that the global terrain would have been adjusted to geoid models, but you’re saying it is not and will globally be incorrect, even within the parameters of ellipsoid correctness?
I don’t know if “correct” or “incorrect” is the right term here. To describe a terrain height, we need to make a choice between two references:
- Height above the WGS84 ellipsoid. This is typically the measurement you would get from a satellite.
- Height above the geoid. This is the value you would get from a ground-based survey.
Cesium uses heights above the WGS84 ellipsoid, as discussed in this older thread. This means that if you have a terrain source which returns geoid heights, those heights need to be converted to ellipsoid heights before rendering them in Cesium. As discussed in the thread, the geoid itself is a large file, so it usually makes sense to do the conversion as a pre-processing step on the input terrain dataset.
For Cesium to render geoid-referenced heights directly, we would have to load the geoid file at render time, in order to render each point at the correct screen position. So far, we have found it more efficient to convert heights to ellipsoid values instead.