1

I'm trying to transform (using pyproj) the same coordinates, first from WGS84, and then from NAD83(2011), and I'm getting the same result:

from pyproj import CRS, Transformer

from_wgs84_transformer = Transformer.from_crs(CRS("WGS84"), CRS("epsg:6415"), allow_ballpark=False)
from_nad83_transformer = Transformer.from_crs(CRS("NAD83(2011)"), CRS("epsg:6415"), allow_ballpark=False)
>>> from_wgs84_transformer.transform(41.15240653663834, -122.85890995637374)
(1927909.814711512, 702339.7864515218)

>>> from_nad83_transformer.transform(41.15240653663834, -122.85890995637374)
(1927909.814711512, 702339.7864515218)

Can someone explain why, and also how to fix the code?

5
  • I could not find any example about the usage as ` Transformer.from_crs(CRS("WGS84"),...`. Where did you find the documentation for that syntax?
    – user30184
    Commented Nov 21, 2023 at 7:56
  • How to you suggest to create the transformation? pyproj4.github.io/pyproj/stable/_modules/pyproj/…
    – paul
    Commented Nov 21, 2023 at 8:03
  • Do you have the transportation grids installed? pyproj4.github.io/pyproj/stable/transformation_grids.html
    – snowman2
    Commented Nov 21, 2023 at 13:51
  • One transformation/operation path could be 7666 which is wgs84(G1762) to ITRF2008 (null transformation) and then 7807, ITRF2008 to NAD83(2011) which is time-based so you need a data epoch or just use the base epoch of the transformation.
    – mkennedy
    Commented Nov 29, 2023 at 21:33
  • @mkennedy How can I make sure this is the correct path to take? btw, can you recommend a source (book/blog/etc) where I can learn all this stuff to its core?
    – paul
    Commented Dec 2, 2023 at 21:50

2 Answers 2

1

You get that result because for Proj NAD83(2011) and WGS 84 mean the same. You can get a full report by testing the transformation with Projinfo.

projinfo -s epsg:6318 -t epsg:4326

Candidate operations found: 1
-------------------------------------
Operation No. 1:

EPSG:9774, NAD83(2011) to WGS 84 (1), 2.0 m ...
...

PROJ string:
+proj=noop
...
SCOPE["(null/copy) Approximation for medium and low accuracy
applications assuming equality between plate-fixed static 
and earth-fixed dynamic CRSs, ignoring static/dynamic CRS 
differences."]
...
    REMARK["For many purposes NAD83(2011) can be considered
to be coincident with WGS 84. This approximation ignores 
the ~2.2m offset of NAD83 from the geocentre, the low 
accuracy of the WGS 84 ensemble and the application 
of tectonic plate motion to WGS 84 data."]]

Unfortunately I do not know which tools can handle the terms that Proj ignores.

4
  • 1
    They're not the same. NAD83(2011) is plate-fixed, while WGS 84 (and ITRFxx) is not. There's about 1-2 m difference between the 2 systems. That transformation has a 2 m accuracy because it's not taking the differences into account.
    – mkennedy
    Commented Nov 29, 2023 at 21:25
  • 1
    And for taking into account the differences also the epoch of the dynamic system should be known. It seems that Proj and GDAL has nowadays support for coordinate epoch gdal.org/user/coordinate_epoch.html.
    – user30184
    Commented Nov 30, 2023 at 6:54
  • @user30184 do you know how to do this in pyproj? I didn't find any reference to "coordinate epoch" in pyproj
    – paul
    Commented Dec 2, 2023 at 21:52
  • Maybe you could try for example EPSG:7665 instead of EPSG:4326. If I understand right it has the epoch included somehow.
    – user30184
    Commented Dec 3, 2023 at 8:41
0

Since NAD83(2011) is plate-fixed, you need to know the time of the coordinate in order to do a transformation, as the relationship between the two frames changes over time. So, like others have stated in comments, you would need to specify the time/epoch of the coordinates to do such a transformation, which is the tt parameter (Input time coordinate(s)) of the transform call. Also, EPSG:6415 is a projected CRS, so passing a lat/lon to from_nad83_transformer in your question doesn't really make much sense.

Also, WGS 84 is not really a 4D CRS, so you might need to use ITRF 2014/2020 instead for it to find the appropriate transformation.

Assuming you want geographic 2D coordinates for NAD83(2011), it would look something like:

from_itrf2020_transformer = Transformer.from_crs(9990, 6318, allow_ballpark=False)
from_itrf2020_transformer .transform(xx=41.15240653663834, yy=-122.85890995637374, tt=2024.0)

See https://pyproj4.github.io/pyproj/stable/examples.html#d-transformations-with-time

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