Curve support in GEOS C API

[Regina Obe]

So this would just be for GEOS 3.15 and above right?  So projects would still need to change if GEOS >= 3.15 to know if curve support is available.

 

That’s fine.  But backporting would not be fine.

 

From: Daniel Baston <dbaston at gmail.com> 
Sent: Wednesday, January 7, 2026 10:07 AM
To: GEOS Development List <geos-devel at lists.osgeo.org>
Subject: Curve support in GEOS C API

 

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

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