I have elevation data for 699 points around Australia. I want to calculate the difference between these point elevations and the highest elevation within 25 nautical miles - in simple terms I want to get a sense of the terrain around each point.
I have been able to obtain the maximum elevation within a 25nm radius using the SRTM-derived 3 Second Digital Elevation Models Version 1.0. However, this DEM uses EGM96 as the vertical datum, whereas my point data is with reference to "mean sea level" which I take to mean AUSGeoid2020.
In order to find the difference between the two elevations I need to transform one set of data to the vertical datum of the other; it would probably be easier to transform my point data to EGM96.
I have downloaded the AUSGeoid2020 ASCII file which, I believe, will permit me to transform the point elevations to the Australian Height Datum (AHD). Now I need to convert from AHD to EGM96...
I've transformed geospatial data between horizontal datums before - in R - but I haven't been able to locate any documentation relating to transforming vertical datums.