A GPS survey for a flood study yields ellipsoid heights. To convert these to NAVD 88 orthometric heights, the surveyor should use:
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A
A constant conversion factor of -32 feet applied nationwide
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B
NOAA's GEOID model (e.g., GEOID18) to compute the geoid-ellipsoid separation
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C
A simple subtraction of the WGS 84 ellipsoid radius
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D
The NGVD 29 to NAVD 88 conversion table only