Curve support in GEOS C API

[Daniel Baston]

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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