ArcGIS Pro now has default transformations which seem off between HARN and NAD83 and/or should I even transform data between HARN and NAD 83 2011?

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08-24-2021 07:45 AM
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LancasterGIS
New Contributor III

Out statewide imagery is projected into NAD 1983 HARN (3753 and 54). When this imagery is brought into a new map in ArcGIS Pro for the corresponding state plane projection, for example NAD83 South (3735), ArcGIS Pro automatically applies the “NAD 1983 to HARN Ohio” transformation, however from everything I can find this transformation is mean to convert to the original NAD83, not NAD83 (2011) – see references below. Also, when I bring in GPS points (4 in accuracy - Trimble R2) collected using our DOT's RTK VRS network which uses the latest NAD revision, the do not align with the imagery when this transformation is being used.

In ArcMap the user had to manually apply a transformation when bringing in data in projection different from the map projection. I am guessing that traditionally many people have just clicked yes in ArcMap to continue without applying a transformation when adding our state imagery, so this may not have been an issue in the past as few people noticed.

So a couple things could be happening - 

  1. The imagery is not in the correct projection and/or has been incorrectly transformed into HARN.
  2. The default ArcGIS Pro transformation should not be used or is not appropriate.
  3. Something else...

Further, from the links below it would seem there is no highly accurate transformation available from EPSG:3754 to EPSG:3735, since this shift would only be a few centimeters.

So the question is should data in NAD83 HARN be transformed when projected to NAD83 2011?

Possibly related to this topic - 

https://community.esri.com/t5/map-projections-questions/nad83-to-nad83-harn-florida-transformation-s...

References

https://gis.stackexchange.com/questions/324377/why-are-there-differences-in-output-position-between-...

https://gis.stackexchange.com/questions/1115/cors-harn-transformations-what-is-the-most-accurate-met...

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