[QGIS-Developer] Non-cartesian buffering

[Alexis R.L.]

Greetings,

I've reached out to the author and it seems doable for a point by using
this method (
https://geographiclib.sourceforge.io/Python/doc/code.html#geographiclib.geodesic.Geodesic.Direct
) and using the azimuth to generate the vertices.

My guess would be that for more complex geometries you'd need to find the
angle to the next node, and only generate vertices that are on the outside.
I'll continue to look into it and do some trials.

Thanks for the pointer.

Alex


Le mer. 24 mai 2023 à 20:47, Nyall Dawson <nyall.dawson at gmail.com> a écrit :

> On Thu, 25 May 2023 at 10:27, Alexis R.L. via QGIS-Developer
> <qgis-developer at lists.osgeo.org> wrote:
> >
> > Greetings,
> >
> > I was looking into buffers and noticed that arc could do geoid buffering
> but it's not something qgis could do yet.
> >
> > Now I'm going to assume that such a thing would usually need to be
> implemented in geos and in one of the ticket asking about this, another
> repository was pointed to ( https://github.com/libgeos/geos/issues/820).
> >
> > That repository being https://github.com/google/s2geometry now I don't
> know how important generating things based on non-cartesian distance is and
> if such tools are to be made if they should be made in QGIS instead of
> relying on external libs.
>
> Unfortunately S2 isn't a sufficiently generic approach in my opinion.
> It is designed completely around a spherical earth assumption, so
> doesn't work for situations where an ellipsoidal model is required
> (and definitely doesn't work for non-earth bodies).
>
> What we need is a library which can perform geographic buffering using
> an ellipsoid. Which doesn't exist yet, but
> https://geographiclib.sourceforge.io/ would be a good place for this
> to exist...
>
> Nyall
>
>
>
>
> >
> > As more and more global and 3D things are added,I assume that those will
> be more important.
> >
> > Thanks,
> >
> > Alex
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