All this stuff looks rather useful: http://geos.osgeo.org/doxygen/classgeos_1_1noding_1_1Noder.html
However, from the GEOS README file:
The C++ interface should not be used directly; the geos project
views it as a bug for another program to use the C++ interface or even
to directly link against the C++ library.
Is there a C interface to the Noding functionality that I'm missing? I can't find it in