Re: A more precise polygon_overlap() - Mailing list pgsql-hackers

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