I have a bunch of North American data points that reference NAVD 27, 83 and WGS 84 ellipsoid for elevations. How can I utilize FME to reproject the vertical data so it references the WGS 84 geoid (EGM96) instead of its current vertical datum?
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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.