Hi Even, Thanks for explaining the difference between the images. You're absolutely right: I indeed assumed the two were using the same ellipsoids. If I use epsg:4269 (nad83 ell.) as the src, all the numbers are consistent.
- Regards Rajsekar On Mon, Jan 10, 2022 at 8:05 PM Even Rouault <[email protected]> wrote: > Rajsekar, > > One of the reason that the -full image is larger than the -small one is > that the former includes > 500 MB of geodetic grids, whereas the later only > includes very basic ones. (I've just amended > https://github.com/OSGeo/gdal/blob/master/docker/README.md to make it > clearer) > > As you do a WGS 84 to NAD83 transformation, the ubuntu-full image can use > the HPGN grids, and in particular the Pennsylviana grid > > $ echo -77.75 40.16666666666666 | PROJ_DEBUG=2 bin/cs2cs > '+init=epsg:4326' '+to' '+init=epsg:2271' > [ ... snip ... ] > Using coordinate operation axis order change (2D) + Inverse of NAD83 to > WGS 84 (57) + SPCS83 Pennsylvania North zone (US Survey feet) > pj_open_lib(us_noaa_pahpgn.tif): call > fopen(/home/even/proj/PROJ-data/us_noaa/us_noaa_pahpgn.tif) - succeeded > 1968499.39 -0.15 0.00 > > Whereas the -small image has no such grid and will assume that NAD83 == > WGS84. > > In theory the result with the -full image should be more accurate, but it > depends if somewhere in your workflow someone has not assumed that NAD83 == > WGS84 ... > > Anyway WGS 84 is literaly a moving and somewhat fuzzy target, so you > shouldn't expect in general results to have an accuracy better than ~ 2m in > any transformation involving it. > > Even > Le 10/01/2022 à 15:21, Rajsekar Manokaran a écrit : > > Hi gdal devs and users, > > I came across a discrepancy in proj. values between ubuntu-small and > ubuntu-full docker images even for the same gdal version tag. I tried to > convert a few coords from epsg:4326 to epsg:2271. The coords are: > > Input: > -77.75 40.16666666666666 # this is the center meridian, lat of 2271 > -75.18094433657971 40.25904959199275 # another sample point > > The outputs of all ubuntu-small-* images seem to be correct, but the > ubuntu-full-* images have about 1 feet error (2271 uses US_SURVEY_FEET > units). > > Here's how I run it: > > $ docker run --rm -i osgeo/gdal:"$tag" cs2cs '+init=epsg:4326' '+to' > '+init=epsg:2271' < input > where tag is the docker tag: "ubuntu-full-3.2.2", or "ubuntu-small-3.4.1", > etc. > > Here are the outputs for the ubuntu-full images: > > output-ubuntu-full-3.2.2 > 1968499.39 -0.15 0.00 > 2685535.97 44295.90 0.00 > output-ubuntu-full-3.3.3 > 1968499.39 -0.15 0.00 > 2685535.97 44295.90 0.00 > output-ubuntu-full-3.4.1 > 1968499.39 -0.15 0.00 > 2685535.97 44295.90 0.00 > > Here are the outputs for the small images: > > output-ubuntu-small-3.2.2 > 1968500.00 -0.00 0.00 > 2685536.18 44296.27 0.00 > output-ubuntu-small-3.3.3 > 1968500.00 -0.00 0.00 > 2685536.18 44296.27 0.00 > output-ubuntu-small-3.4.1 > 1968500.00 -0.00 0.00 > 2685536.18 44296.27 0.00 > > The first input is the center and so should translate to "(false east, > false north)". Going by that, the small versions seem to be more correct. > Any idea why this difference in the values? > > - > Rajsekar > > > > _______________________________________________ > gdal-dev mailing > [email protected]https://lists.osgeo.org/mailman/listinfo/gdal-dev > > -- http://www.spatialys.com > My software is free, but my time generally not. > >
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