[R-sig-Geo] Offering an alternative to GPC.

[Angus Johnson]

  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