[Proj] Vertical Datum Shift

[Daniel Komisar]

I'm having trouble figuring out how to the the +geoidgrids option. I'm trying to 
convert EGM96 values to WGS84 with cs2cs (I will eventually be converting a dted 
file but first I'm trying to just get this to work) and I cannot get it to alter 
the values so I'm doing something wrong. Using 4.7.1.

cs2cs +proj=latlong +ellps=WGS84 +datum=WGS84 +geoidgrids=egm96_15.gtx +to 
+proj=latlong +ellps=WGS84 +datum=WGS84

It always outputs the exact same numbers I put in.

Thanks.