Greg,
There's a high chance for this to be completely PROJ behavior. GDAL
hardly knows about CRS those days :-)
Could you share your input and output files ?
Also set CPL_DEBUG=PROJ and PROJ_DEBUG=2 as environment variables to see
which transformations PROJ pickup : look for lines starting with "PROJ:
Using coordinate operation ..."
With latest PROJ master (and also 6.3.2), I see that
projinfo -s EPSG:6319 -t EPSG:7912 -o PROJ
Candidate operations found: 1
-------------------------------------
Operation No. 1:
unknown id, Conversion from NAD83(2011) (geog3D) to NAD83(2011)
(geocentric) + Inverse of ITRF2014 to NAD83(2011) (1) + Conversion from
ITRF2014 (geocentric) to ITRF2014 (geog3D), 0 m, Puerto Rico - onshore
and offshore. United States (USA) onshore and offshore - Alabama;
Alaska; Arizona; Arkansas; California; Colorado; Connecticut; Delaware;
Florida; Georgia; Idaho; Illinois; Indiana; Iowa; Kansas; Kentucky;
Louisiana; Maine; Maryland; Massachusetts; Michigan; Minnesota;
Mississippi; Missouri; Montana; Nebraska; Nevada; New Hampshire; New
Jersey; New Mexico; New York; North Carolina; North Dakota; Ohio;
Oklahoma; Oregon; Pennsylvania; Rhode Island; South Carolina; South
Dakota; Tennessee; Texas; Utah; Vermont; Virginia; Washington; West
Virginia; Wisconsin; Wyoming. US Virgin Islands - onshore and offshore.
PROJ string:
+proj=pipeline
+step +proj=axisswap +order=2,1
+step +proj=unitconvert +xy_in=deg +z_in=m +xy_out=rad +z_out=m
+step +proj=cart +ellps=GRS80
+step +inv +proj=helmert +x=1.0053 +y=-1.9092 +z=-0.5416 +rx=0.0267814
+ry=-0.0004203 +rz=0.0109321 +s=0.00037 +dx=0.0008 +dy=-0.0006
+dz=-0.0014 +drx=6.67e-05 +dry=-0.0007574 +drz=-5.13e-05 +ds=-7e-05
+t_epoch=2010 +convention=coordinate_frame
+step +inv +proj=cart +ellps=GRS80
+step +proj=unitconvert +xy_in=rad +z_in=m +xy_out=deg +z_out=m
+step +proj=axisswap +order=2,1
So it applies a time-dependent Helmert transformation, which has also
non-time dependent terms.
However trying a bit, the transformation seems to introduce a shift of
about ~1 m or so, not 35 m
$ echo 50 -100 0 | cs2cs -d 8 EPSG:6319 EPSG:7912
50.00000754 -100.00001400 -0.68652183
$ echo 50 -100 50.00000754 -100.00001400 | geod -I +ellps=GRS80
-50d7'11.377" 129d52'48.584" 1.308
Even
Le 24/04/2021 à 16:39, Greg Troxel a écrit :
Even Rouault <[email protected]> writes:
- http://download.osgeo.org/gdal/3.3.0/gdal-3.3.0beta1.tar.gz
The tl;dr is:
- I'm seeing bad transforms NAD83/ITRF with 3.3.0beta1 but I do not
have any basis to blame 3.3.0 because a lot of other things are in
flux.
- If you are using 3.3.0beta1 and transforms I suggest looking at your
output data.
I have noticed a problem but I have little idea where it is. I will be
looking into it myself but I wanted to mention it so that others could
be on the lookout.
Besides updating to gdal, I'm doing a general software freshening and
rebuilding lots of things, but aside from the gdal beta my geo packages
haven't changed versions. I have proj 6.3.2 with installed grids, which
was just rebuilt.
The background is that I'm mostly working in EPSG:6319 which is
NAD83(2011).
I transform to EPSG:7912 which is ITRF2014 to display the data on
leaflet webmaps (as a proxy for WGS84 to avoid null transforms).
I noticed that my points on the webmap were very far off, displaced very
roughly 35m ESE. I then put an NAD83 version in the webspace, and that
made things look ok (with the ~1 meter error from treating NAD83 and
ITRF2014 as equal, surely).
I'm extracting things from a geopackage in 6319 like
ogr2ogr -f GeoJSON -t_srs "EPSG:7912" -s_srs "EPSG:6319"
FOO/issues.geojson foo.gpkg issues
ogr2ogr -f GeoJSON -t_srs "EPSG:6319" -s_srs "EPSG:6319"
FOO/issues-nad83.geojson foo.gpkg issues
which has previously been fine. I'm definitely getting very large
offsets from two files extracted seconds apart from the very same
geopackage.
So this is not a request for help, but if you are using ogr2ogr to
transform datums, and you are using gdal 3.3.0beta1 especially with proj
6, I'd suggest a quick look at your output data to see if it seems ok.
I will be retesting after all the software rebuilds are done, and
rolling back to released gdal. (Yes, I know proj 6.3 is old and that I
should update.)
Thanks,
Greg
--
http://www.spatialys.com
My software is free, but my time generally not.
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