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I am looking for a way to compute the approximate HAE (height above ellipsoid of WGS84) of a point at the surface of the Earth at a specific latitude and longitude. Is there a simple way to get this information? Is this even possible? The most convenient way for me would be to use some Python library if there exists one that does that.

This is because I need to find the altitude of a flying object with respect to the surface of the Earth, and the object GPS only gives its HAE therefore I also need the HAE of the surface.

Vince
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Lelouch
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  • The HAE I measure is the HAE of a flying object, therefore it is not on the ground. The HAE of the surface would be the HAE measured it it was actually on the ground. @KadirŞahbaz I am truly interested into the difference between these two values since I am looking for an approximation of the altitude wrt to the ground and not to some theoretical ellipsoid. I guess I'll have to use some geoid thing somewhere. – Lelouch Mar 21 '23 at 10:52
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    If I understood well I have to use some SRTM data that will give me MSL altitude, then I need to use the WGS84 geoid (EGM96) to compute the geoid height (Hgeoid) and I can get my HAE height with HAE = MSL+Hgeoid . Maybe there is something that does all of this directly – Lelouch Mar 21 '23 at 11:07
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    Use WGS84 ellipsoid height, if you are using GPS coordinates of the flying object you can compute the difference directly. No need to use geoid or MSL here, unless the GPS height value is orthometric height instead of ellipsoidal height. – aldo_tapia Mar 21 '23 at 11:36
  • Yes, you need some terrain model, which are usually referenced to a geoid. So also need to transform the model elevations from geoid to ellipsoid, or the object elevation from ellipsoid to geoid. For the terrain model, maybe python-srtm (more like an old surface model, but probably enough). For the conversions maybe pyproj. If you downloaded the terrain model, maybe can do all with gdal. – Gabriel De Luca Mar 21 '23 at 14:03
  • If you have a GNSS height you have the height above the surface but that surface is expressed as the height above the WGS84 ellipsoid. It sounds like you are intereseted in getting the height above the geoid (some orthometric height). See here for information on vertical datums and tools to do those transformations using vDatum: https://vdatum.noaa.gov/welcome.html. See here for converting WGS84 ellipsoid heights to geoid heights using pyproj. https://gis.stackexchange.com/questions/340392/vertical-datum-transformation-using-pyproj – GBG Mar 21 '23 at 15:30

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