On Tue, Mar 20, 2012 at 6:51 PM, Simon Greener <si...@spatialdbadvisor.com> wrote: > I looked at this in Oracle many years ago. > I would have thought number of vertices is an unreliable measure of > complexity - how > do we know that any one straight line is not described by a lot more than a > start and > end node?
True, but if a line, which could be described by only 2 points, is described by 100s, doesn't the algorithm still take longer? Isn't removing the redundancies part of what simplification does? I tried ST_Simplify, and using ST_npoints (thanks Sandro!), I was able to get some measure of how much simpler the shapes were - or at least, how many fewer data points the algorithm had to consider - as I gradually simplified them more and more. I found that using ST_within on multi-polygons with >11k points is pretty slow, and our multi-polygons with the most points (~35k) were VERY slow. We dropped the slowest ones down to around 2000 points, and they're much faster. I'm still concerned about accuracy, though. > If one can remove or reduce such vertex complexity then triangulating the > polygon and > counting the triangles may be a better measure. Perhaps looks at > ST_SimplifyPreserveTopology() > with very small tolerances first. Thanks for the suggestion, I'll check it out. I'm not familiar enough with the terms to understand how it's different from ST_Simplify, but I'm still learning. Thank you both for your help! _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users