I'm adding property line info for 80 parcels to existing mapping from a few years ago for a project to bury all the electric lines in town (Cruz Bay, St. John). I have a tight closed loop with a robot aligned to 4 GPS OPUS SPC points, all within 0.10'. But I'm missing the old mapping (1 control point from the company that did the mapping with GNSS) and over a dozen manholes, catch basins, curbs etc. by a consistent 3.7'N, 1.4'E. I had a problem with US Feet / Int. Feet on another project, but that was more E than N as the numbers are greater, so that's not it. I can just move all my work to match the old and it will be all good, but me and the guy that did the mapping would like to know what's up. Any ideas?
That type of little shift is usually international feet vs US feet or SPC adjusted to surface around a point. Without Metadata I would either hold the design control or move their data over universally to SPC.
My first guess would be that the older GNSS mapping data was mistakenly processed against an autonomous position rather than a published or adjusted position.
Or, if they processed it against an OPUS solution, someone could have screwed up and entered one or both of the ITRF geodetic values rather than NAD83 values. Seen that before too.
Or someone managed to grab all the points in CAD and move 'em somehow...
I'll just move mine to match. It's kind of backward - construction has started but no one knows where the property lines are, so easement acquisition can't start until I finish drawing all the property lines. Our power co. would be right at home in Texas.
That looks like the offset between WGS84 and NAD83. In Topcon Magnet many people will incorrectly use NAD83/2011 settings when should use NAD83_NO_TRANS . In my area, the difference is 3.78 ft.