I have few thousand rasters in AK zone 4 state plane on NAD83 and in UTM5/6 on GRS 80 that I am trying to mosaic into Web Mercator. ArcGIS (10. 4.1) is reporting that I need a transformation but I do not see an esri transformation for it. I understand that the ellipsoids are almost the same. NOAA/NOS's VDatum: A tutorial on datums enter image description here

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1 Answer 1


I looked for an already existing question, but wasn't able to find one.

GRS80 is an ellipsoid (spheroid in Esri software), not an actual geodetic datum or coordinate reference system. If Esri software is given data that only has a grs80 and no other datum information, we'll build a GRS80-based geographic coordinate [reference] system.

Because it's not an actual GeoCRS (datum), there are no available transformations for it.

You could assume that they're all actually NAD 1983, and redefine the coordinate systems to use the standard NAD 1983 geographic coordinate system. Or you could create a custom geographic transformation using the tool. You could either use all zeroes for the parameter values and pick the geocentric translation method.

  • Thanks for the input. They are most likely on the NAD83 datum (using the GRS80 ellipsoid) and then projecting into a UTM zone. So, if this assumption is right I will see a shift in the data when I put it onto the WGS84 datum (about 4.5 meters in my area -- enough to be a problem for the project). Redefining the CRS will be hard as they are in write protected folder. So, I will be stuck with a custom transformation. What is weird is that the people who had originally built the fist old mosaic did not account for this. I guess it could be on the an old WGS84 datum using the GRS80 ellipsoid.
    – fallingdog
    Apr 20, 2017 at 23:25

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