[geos-devel] QD (Quad-Double) Approach to Robustness

[Paul Ramsey]

In a conversation with Dale Lutz at GeoAlberta, he mentioned they had  
experimented with using the QD library (<http://crd.lbl.gov/~dhbailey/ 
mpdist/>) in some of their topology processing and found that it was  
exceptionally good at bypassing problems caused by reduced  
precision.  Presumably this is because all the input data is at  
double precision, at most, so relative to the processing precision  
(quad) it is quite well behaved.  The approach was so good that in a  
race between the old algorithms (double precision but with lots of  
tests and bobbing and weaving to catch special cases) and the new  
(quad precision, with no special cases at all, just naive algorithms)  
the qd won hands down.  So the overhead of the math library on all  
cases was not higher than the overhead of finding and handling the  
special cases.

Something to look at!

P