What is the difference between horizontal transformations using the ArcMap Project Tool and NOAA VDatum for transforming WGS84 (ITRF00) to NAD83? Which one is more accurate?

[KelseyMcDonald]

I've noticed a ~30cm horizontal difference between data that I transformed from WGS84 (ITRF00) to NAD83 using the ArcMap Project Tool and the same points transformed using NOAA's Vertical Datum Transformation Tool (VDatum). Is there a difference in the parameters used in these transformations? Is one more accurate? Or did I do something funky? Unfortunately, this small of an error could make a big difference for my data, which was collected by RTK and should be accurate to ~2cm. I saw that the WGS_1984_(ITRF00)_To_NAD_1983 transformation has an accuracy of 0.10m, which is less accurate than I would like. It seems like the difference between the two should not be more than 3x the published accuracy, so I think I must be missing something. Let me know if you have thoughts on the best transformation method to use. Thank you for your help!!

[MelitaKennedy · Accepted solution]

If your data's RTK then it's not on NAD 1983. You'll get access to other transformations if you use a later realization like NAD 1983 (2011) or NSRS2007. I would recommend using WGS_1984_(ITRF08)_To_NAD_1983_2011 instead, for instance.

Equation-based transformations (coordinate frame, position vector, Molodensky-Badekas, geocentric translations) will also give (slightly) different results if you run them with or without ellipsoidal heights.