This might be a possible fit:
http://www.magic-software.com/Applications.html
(see "Boolean operations on 2D polygons. Based on BSP trees" near the
bottom of the page).

The license agreement might be acceptable.  I'm not a lawyer, so I can't
be sure how free it really is to use from reading this:
http://www.magic-software.com/License/free.pdf

It would probably be good to contact the author.
http://www.magic-software.com/CompanyInfo.html

Wed, 22 May 2002 14:15:49 -0700
"Dann Corbit" <DCorbit@connx.com>
Re: A more precise polygon_overlap()
See http://www.vividsolutions.com/jts/jtshome.htm for a robust set of
algorithms in Java which do all the spatial predicates (the 3x3
Egenhofer matrix). Also union, difference, and buffer. It is licenced
LGPL. Also see PostGIS (http://postgis.refractions.net) (licenced GPL)
for a set of PostgreSQL GIS objects. We are currently working on porting
JTS algorithms to C++ for use in PostGIS.

P.

Dann Corbit wrote:
> 
> This might be a possible fit:
> http://www.magic-software.com/Applications.html
> (see "Boolean operations on 2D polygons. Based on BSP trees" near the
> bottom of the page).
> 
> The license agreement might be acceptable.  I'm not a lawyer, so I can't
> be sure how free it really is to use from reading this:
> http://www.magic-software.com/License/free.pdf
> 
> It would probably be good to contact the author.
> http://www.magic-software.com/CompanyInfo.html
> 
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> TIP 5: Have you checked our extensive FAQ?
> 
> http://www.postgresql.org/users-lounge/docs/faq.html

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     | Paul Ramsey
     | Refractions Research
     | Email: pramsey@refractions.net
     | Phone: (250) 885-0632
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Wed, 22 May 2002 17:09:49 -0700
Paul Ramsey <pramsey@refractions.net>
Re: A more precise polygon_overlap()