How do I apply a geoid model to a one-step transformation?
The three important things to remember if you are going to apply a geoid model to a one-step transformation are: The geoid model must be selected before the points are matched. No points are to be matched vertically. The base must have a correct known ellipsoidal height. My thanks to Henri Ayers for the following information: All of the following cases are valid as long as the Geoid Field File is coming from a “WGS84” Geoid Model and is being selected “before” matching the horizontal (2-D position only) coordinates of the local points with the corresponding WGS84 coordinates. No points should be matched in vertical to prevent using the vertical (1-D vertical shift only or 1-D vertical shift with 2-D best-fit plane tilting parameters) transformation parameter(s) and therefore bypassing the use of Geoid Model to obtain Local (Orthometric) heights. The WGS84 Geoid Model will be used to directly convert WGS84 Ellipsoid Heights to Orthometric Heights and vice versa without affecting the 1-S
