Append(merge,copy,..) two point Layers (GPS GNSS points) with different epochs 2017.50 and 2025.00

Question

In ArcGIS Pro, I need to copy (or merge or append) two-point feature classes (GPS GNSS points) that share identical schemas but exist in different epochs. Layer A was collected at Epoch 2017.50, while Layer B was at Epoch 2025.00. Both are in NAD 1983 StatePlane California V FIPS 0405 (US Feet)

What is the standard GIS/ survey workflow to append Layer A into Layer B? My current 'Calculate Geometry' test after appending one layer to another layer resulted shifts in Northing and Easting ( decimals). What transformation settings should I use to reconcile these two different epochs? As much as I understand copying (merging, appending) them directly without transformation(HTDP , python coding, Perform a Time-Dependent Transformation,) will cause misalignment because the Earth's crust has moved between those dates. Both data are collected in 2025 (Jan 2025 and November 2025)

MelitaKennedy · Answer

Hello,

My colleague, Kevin M. Kelly, asked me to post a reply because he's having trouble accessing Esri Community.

Currently, functionality does not yet exist in ArcGIS Pro or any other Esri product to perform a point motion operation to update coordinates over time. We are working hard to build this functionality but it is not there yet.

It seems you want to update your CSRS Epoch 2017.50 (NAD83) projected coordinates (NAD 1983 StatePlane California V FIPS 0405 (US Feet)) at epoch 2017.50 to CSRN Epoch 2025.00 (NAD83 2011) State Plane coordinates at epoch 2025.0. Again, this is not yet possible in ArcGIS. The only tool available to correctly perform this point motion operation is the SOPAC Coordinate Interpolator Prompt (SCIP). Unfortunately, this tool does not handle GIS datasets but only single points or a list of points in CSV format.

Be aware that the NGS HTDP tool will not yield the same results as the SOPAC Coordinate Interpolator Prompt (SCIP) tool. This is because NGS and SOPAC used different geophysical models and analysis methods to derive the California crustal motion models. This is clear from the comparison below between HTDP and SCIP for point motion from 2017.5 to 2025.0 at station 7ODM in Southern California (see values in bold text). Note for the SCIP calculation I used the online tool with a single point rather than a CSV file.

HTDP Output

****************************************

HTDP OUTPUT, VERSION 3.6.0

TRANSFORMING POSITIONS FROM NAD_83(2011/CORS96/2007) (EPOCH = 07-02-2017 (2017.5000))
                         TO NAD_83(2011/CORS96/2007) (EPOCH = 01-01-2025 (2025.0000))

70DM                   
  LATITUDE     34 06 59.05950 N     34 06 59.06426 N       18.64 mm/yr  north
  LONGITUDE   117 05 35.45393 W    117 05 35.45786 W      -13.46 mm/yr  east
  ELLIP. HT.             762.791             762.785 m     -1.22 mm/yr  up
  X                 -2407750.342        -2407750.392 m     -6.76 mm/yr
  Y                 -4706537.770        -4706537.646 m     16.34 mm/yr
  Z                  3557571.660         3557571.778 m     14.75 mm/yr

SOPAC Coordinate Interpolator Prompt

T-in                            2017.5000 (2017-07-02)
T-out                           2025.0000 (2025-01-01)
Closest Input Date              20170705
Closest Output Date             20250106
Input Datum                     NAD83(2011)
T-in Latitude (N)                 34 6 59.0595
T-in Longitude (E)              -117 5 35.4539
T-in Ellipsoidal /height (m)        762.7910
Output Datum                    NAD83(2011)
T-out Latitude (N)                34 6 59.0641
T-out Longitude (E)             -117 5 35.4581
T-out Ellipsoidal /height (m)       762.7980
East Diff. (mm) (t-out - t-in)     -106.6
North Diff. (mm) (t-out - t-in)    140.5
Up Diff. (mm) (t-out - t-in)       7.0
East Unc. (mm)                     2.4
North Unc. (mm)                    2.7
Up Unc. (mm)                       11.1

I hope this helps.

Kevin (and Melita)

SarmenBajari · Answer

Thank you, I also got this answer from Reddit.

ZenMasterZeke · Answer

Try calculating using Round(coordinate, 4)  on each coordinate. Change the 4 to however many decimals are appropriate for your situation. Your Before coordinates are likely just displaying two decimal points, with actual values being longer.

Coordinates shouldn't have shifted if both epochs used the same coordinate system, but it's very difficult to get exactly the same coordinates on separate readings. If your numbers are in meters, for example, the third decimal would be 1000th of a meter. You're starting to get into accuracy levels of the GPS at that stage. It might be helpful to consider coordinates identical if the difference between them is below a threshold, rather than matching precisely.