[geos-devel] PolygonBuilder::findShell assertion 'shellcount <= 1' failed

[kyle cronan]

Hi everyone,

I ran into this assertion failure while developing a python script
that uses Shapely 1.2.3 with GEOS 3.2.2.  My program makes it most of
the way through a large dataset and then gives this message:

python: PolygonBuilder.cpp:261: geos::geomgraph::EdgeRing*
geos::operation::overlay::PolygonBuilder::findShell(std::vector<geos::operation::overlay::MinimalEdgeRing*,
std::allocator<geos::operation::overlay::MinimalEdgeRing*> >*):
Assertion `shellCount <= 1' failed.

I figured I'd try to isolate some code that can recreate the problem,
and see if I can get the same behavior with some test code in C, but
first I just wanted to ask what this failure is all about.  And what
is a minimal edge ring?  Any pointers that could help me understand
how to debug the problem would be appreciated.

Thanks,
Kyle Cronan
<kyle at pbx.org>