While I'm not an R user, I noticed a couple of months ago some posters
in this mailing list were looking at ways to address the commercial
licensing restrictions associated with General Polygon Clipper (GPC).
I'd like to offer to the RGEOS community my own recently developed
polygon clipping library - 'Clipper'. I believe Clipper -
http://sourceforge.net/projects/polyclipping/ - has a couple of
significant advantages over GPC:
1. the licensing (MPL 1.1 or LGPL2.1) is much less restrictive and
doesn't require payment for commercial uses.
2. my testing indicates that Clipper is both significantly faster and
also more robust that GPC (see
http://angusj.com/delphi/clipper.php#features ).
Clipper was initially written in Delphi, but I've also translated the
library into C++.
There's also a DLL (for Window's users) that exports functions to
perform the boolean clipping algorithms (intersection, union, difference
& xor).
I'm afraid documentation is still very thin, but there is a demo in the
download package which shows that basics. Nevertheless, the public
methods of Clipper C++ class (or TClipper Delphi class) are relatively
few and fairly well documented with in the code (though much more
extensive in the Delphi code).
Hope that helps ...
Angus
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