This question moved me to implement an easy idea I had on mind https://github.com/OSGeo/PROJ/pull/4418
The result is here: https://osgeo-proj--4418.org.readthedocs.build/en/4418/operations/projections/all_images.html (This is not solving your problem. It is just collecting a bunch of images) On Sun, 9 Mar 2025, 00:13 Michael Sumner, <[email protected]> wrote: > In the past I've had success filtering out bad segments that are "long" > (in native CRS), for example with omerc. I guess we could generate spanning > segments across the grid domain (maybe with a rectangle or triangle grid > from longlat)and analytically find that boundary (endpoint pixels that have > segments that are "too long). > > I think this would work for omerc and spilhaus, not sure about generally. > Certainly repointing polygons back together is much harder and probably > needs mesh decomposition. > > Will try, very interested in this discussion. > > Cheers, Mike > > On Sun, Mar 9, 2025, 08:27 Javier Jimenez Shaw via PROJ < > [email protected]> wrote: > >> Implementing the Spilhaus projection I learned how the images in the >> documentation are generated, like the one in >> https://proj.org/en/latest/operations/projections/spilhaus.html >> if you have a look at docs/plot/plotdefs.json you will see that the >> workaround is to not plot very long lines, that are usually crossing from >> one border of the projection to another. >> >> On Sat, 8 Mar 2025 at 22:03, Nyall Dawson <[email protected]> wrote: >> >>> On Sun, 9 Mar 2025 at 04:06, Javier Jimenez Shaw <[email protected]> >>> wrote: >>> > >>> > If you mean in a generic way, I think the answer is no. >>> > Each projection has its own peculiarities and behaviours. Spilhaus (by >>> the way, not yet in PROJ, but coming in 9.6.0) is a good example. >>> >>> Testing Spilhaus in QGIS was actually the motivation for this >>> question. It works fine for rasters, but for vectors there's extreme >>> artifacts caused by rendering features crossing the boundaries of this >>> projection. >>> >>> > >>> > "... latitude (or projected x coordinate) " Do you mean longitude? See >>> that the longitude you are looking for may depend on the latitude. >>> >>> 🤦 of course! (*although for the above mentioned Spilhaus projection I >>> guess we'd need something more complex than a single line longitude >>> line anyway!) >>> >>> Nyall >>> >>> > >>> > >>> > On Sat, 8 Mar 2025 at 07:30, Nyall Dawson via PROJ < >>> [email protected]> wrote: >>> >> >>> >> Hi list, >>> >> >>> >> A question: given an arbitrary projection/CRS, is it possible to >>> determine the latitude (or projected x coordinate) at which features would >>> need to be "cut" in order to avoid artifacts when those features wrap >>> around the projection extremes. >>> >> >>> >> Eg if it was EPSG:4326, we'd need to cut the features at +/- 180. But >>> if it's another projection... say mercator or spilhaus or ... is there any >>> way to reliably determine this cutting line? >>> >> >>> >> Nyall >>> >> >>> >> _______________________________________________ >>> >> PROJ mailing list >>> >> [email protected] >>> >> https://lists.osgeo.org/mailman/listinfo/proj >>> >> _______________________________________________ >> PROJ mailing list >> [email protected] >> https://lists.osgeo.org/mailman/listinfo/proj >> >
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