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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?

Question asked by KelseyMcDonald on Jun 29, 2016
Latest reply on Jul 1, 2016 by MKennedy-esristaff

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!!