GEOS (Geometry Engine - Open Source) is a C++ port of the
Java Topology Suite (JTS). As such, it aims to contain the complete
functionality of JTS in C++. This includes all the OpenGIS "Simple
Features for SQL" spatial predicate functions and spatial operators,
as well as specific JTS topology functions such as IsValid().

WWW: http://trac.osgeo.org/geos/
