Vertical Datum reprojection

To reproject your data from the specified vertical datum to EGM96, you need to do a combination of one or more of the following transforms:    WGS84 ellipsoid -> EGM96 CsmapReprojector with these settings:

 

vertical handling: 'Geocentric or ellipsoid height -> Orthometric Height', Geoid height grid: FME_HOME\\Reproject\\GeoidHeightGrids\\World\\Egm96-Wgs84.gdc

 

LL84 as both source and dest CS   NAVD83 (assuming this means NAD83+NAVD88) -> WGS84 ellipsoid CsmapReprojector with these settings:

 

vertical handling: 'Orthometric Height -> Geocentric or ellipsoid height', Geoid height grid: FME_HOME\\Reproject\\GeoidHeightGrids\\Usa\\Geoid*-Nad83_Navd88-*.gdc, (source CS: LL83 -> destination CS: LL84)   NAVD27 (assuming this means NAD27+NGVD29) -> NAD83+NAVD88 CsmapReprojector  with these settings:

 

vertical handling: 'NAD27 heights in NGVD29; NAD83 heights in NAVD88', Source CS: LL27 -> Destination CS: LL83 (more steps required if horizontal and vertical datums are not currently in sync)

 

So, to go from NAD27+NGVD29 to EGM96 you need to do 3 vertical transforms in this order:

 

 

NAD27+NGVD29 => NAD83+NAVD88 => WGS84 ellipsoid height => EGM96

 

 

NAD83+NAVD88 =>  EGM96 requires 2 steps:

 

NAD83+NAVD88 => WGS84 ellipsoid height => EGM96

 

 

and WGS84 ellipsoid height => EGM96 is just one step.

 

 

Hope this helps.