There are a lot of realizations for WGS84: WGS84 (G730), WGS84 (G873), WGS84 (G1150), WGS84 (G1674), WGS84 (G1762), and WGS84 (G2139); and the “Transit” in ArcGIS.
There are transformations between these realizations, or at least there is a transformation between G1761’(?) and G2139. However, there is no transformation between these GCSs if I try to project them into each other. I see, that the translation part is small to be important (https://earth-info.nga.mil/php/download.php?file=(U)WGS%2084(G2139).pdf), but why are these transformations missing from ArcGIS?
If I use an RTK GNSS, do I get the WGS84 coordinates in the current realization? Or does it depend on the chip/settings?
I see a lot of 3D coordinate systems in ArcGIS like WGS 1984 3D, EPSG 4979. What is the purpose of this GCS? Is it an ECEF (Earth Centered, Earth Fixed) cartesian coordinate system? (Probably not, the unit is degree, instead of meter.) If it is a real 3D why is it possible to create a feature class with this coordinate system without Z?
Are real ECEF coordinate systems supported by ArcGIS?
If you have a RTK GNSS the resulting coordinate system depends on your RTK provider. The settings of RTK caster is inherited by the rover practically (technically the output is always in WGS84, but the position is estimated relatively to the base station which could express the coordinates in different GCS and due to the relative manner of calculation the resulting coordinate inherits the base's GCS).
