For x/y or lat/lon or heights between different ellipsoid, we can do conversion by using proj.4. But I found that if I want to convert between WGS84 height and local height, I found that it is not so simple.
For example, I try to convert height of EPSG:5738 which is Hong Kong Principal Datum from WGS84 height. As it proj.4 file is blank, I cannot do it.
From the official description of HKPD (http://www.geodetic.gov.hk/smo/gsi/Data/pdf/explanatorynotes.pdf), it just shows the rough relationship.
Does it mean I have no luck with doing it in proj.4 or other tools?