A customer had some questions on why Esri has "null" or "bookkeeping" transformations as well as why there are transformations which have the same parameter values, but convert between multiple geographic coordinate systems. Here's what I wrote off the top of my head.
- WGS84 is actually not accessible to normal consumers because it’s a military system. Yes, GPS reports WGS84, but in a degraded state. RTK/post-processing are actually linking to ITRFxx or local GCS/datum like NAD83 (2011).
- A lot of data is labeled NAD83 but is really another realization like NAD83 HARN or CORS96 or worse, a mix of several realizations as the dataset has been edited over the years.
