[gdal-dev] GDAL 3.3.0beta1 available

Sat Apr 24 08:13:39 PDT 2021

Just one idea: which time is setting GDAL (and/or PROJ understanding) on
the transformation if nothing is specified? Is it the same as in cs2cs?
That transformation is time dependent.
I read somewhere that the "default" value is not the same (but my memory is
not very reliable).

Cheers.
.___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
Entre dos pensamientos racionales
hay infinitos pensamientos irracionales.

On Sat, 24 Apr 2021 at 16:58, Even Rouault <even.rouault at spatialys.com>
wrote:

> 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 <even.rouault at spatialys.com> 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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