Jonathan Franklin wrote:
On Mon, Nov 16, 2009 at 7:06 AM, Brandon Kohn <blkohn@hotmail.com> wrote:
One of the more useful features of the library (GGL) would of course be the boolean operations. The problem however is clearly going to be robustness.
For some.
I have never encountered a robust floating point boolean operation library in my 9 years of working in the geometry domain. While this may not mean it's impossible, I think it does mean it's unlikely.
I believe that this is because for many use-cases, it isn't worth the run-time performance and development-time trade-off.
The acceptability may depend on the failure mode; it is "looks OK but subtly imperfect", "wrong but valid output", "invalid output", "runs forever", "segfaults", or "reformats disk"? A while ago, Fernando Cacciola posted some links to a set of presentations and papers about FP line intersection robustness that I found very enlightening: http://www.mpi-inf.mpg.de/departments/d1/ClassroomExamples/ or directly to the PDF: http://www.mpi-inf.mpg.de/~kettner/pub/nonrobust_cgta_06.pdf I strongly encourage anyone who wants to express an opinion on this subject in the context of the current review to look at this material; it is very accessible and on page 2 there's a compelling example of what can go wrong. Personally, I find it better to use fixed point (e.g. for latitude/longitude) and relax knowing that I don't have to worry. Regards, Phil.