[PROJ] Determine "cut line" for arbitrary projection

[Javier Jimenez Shaw]

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 <nyall.dawson at gmail.com> wrote:

> On Sun, 9 Mar 2025 at 04:06, Javier Jimenez Shaw <j1 at jimenezshaw.com>
> 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 <proj at lists.osgeo.org>
> 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
> >> PROJ at lists.osgeo.org
> >> https://lists.osgeo.org/mailman/listinfo/proj
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20250308/9f20888c/attachment.htm>