I've read things all over the internet which claim that NAD83 and WGS84 are effectively equivalent (with minor ellipsoid differences). However, if I do geodetic (WGS84) -> ECEF -> geodetic (NAD83) conversions, using only the WGS84 and GRS80 ellipsoid parameters and no Helmert transformation, I can't replicate the results of government sponsored online converters like this one. My geodetic/ecef conversions are done following EPSG note 7.2 and have been rigorously tested for correctness.
Thus my questions are:
- Is a Helmert transform required to convert WGS84 to NAD83?
- Are there canonical or official coefficient values for doing so? I know there are variants of NAD83 and WGS84 over time, but I'm interested in coefficients that would be used today (I think that means NAD83 (2011) and WGS 84 (G1674)?)