I want to calculate the height of an object based on nearest ground surface. I have GPS coordinates and GPS elevation(which I assume is ellipsoid height) as an input in WGS84 coordinate system. I read through some basics and it seems I have to convert this ellipsoid height to orthometric height which I guess is roughly equivalent to Above Mean Sea Level (AMSL), correct?
I'm not 100% sure if 122.6m ellipsoid height for GPS location 47.662511,-122.152067 is correct or not?
Please also let me know if I want to get accurate height am I following correct approach?
I may have to again convert NAVD88 to AMSL for more accuracy right?