Curve support in GEOS C API

[Daniel Baston]

Thanks, I figured there was a reason I hadn't seen this pattern in the wild
:)

Dan

On Wed, Jan 7, 2026 at 10:31 AM Even Rouault <even.rouault at spatialys.com>
wrote:

> Dan,
>
> Just commenting on your last question. I don't think using function
> pointers is feasible. I've vague memories of past times where I tried
> this and I remember that at least on Windows, with shared libraries, the
> address of a function inside the library is not the same as the address
> an external user gets, due to how the dynamic loader works (typically
> the address an external user gets is the one of some "trampoline"
> function that then jumps to the actual address inside the library)
>
> Even
>
> Le 07/01/2026 à 16:06, Daniel Baston a écrit :
> > Hi,
> >
> > I have been incrementally adding curve support in GEOS, for example in
> > https://github.com/libgeos/geos/pull/1347. I've been thinking about
> > the best way for applications such as QGIS/PostGIS/GDAL to integrate
> > this functionality.
> >
> > Currently, these applications linearize all geometries before sending
> > them to GEOS. That will not be necessary for GEOSNode and a list of
> > functions that will likely increase over multiple GEOS releases. It
> > seems cumbersome for applications to rely on GEOS version checks to
> > know if linearization is needed, so I think GEOS should offer an
> > ability to automatically linearize inputs and curvify outputs where
> > needed. The parameters for this conversion (and whether to perform it
> > all) could be held by the context handle, and controlled with
> > functions like GEOSContext_setCurveToLine([ DISABLED / STEP_DEGREES /
> > MAX_DEVIATION ]) and GEOSContext_setLineToCurve([ DISABLED /
> > SOME_OTHER_TOLERANCE]). I would also expose a
> > GEOSCurveToLine(GEOSGeometry*, params) and
> > GEOSLineToCurve(GEOSGeometry*, params).
> >
> > If needed, we could also provide a capabilities function that would
> > take a function name (or pointer?) and report whether the function
> > supports curves in the current GEOS version.
> >
> > Does this seem like a reasonable approach?
> >
> > Dan
>
> --
> http://www.spatialys.com
> My software is free, but my time generally not.
>
>
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