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On 08/08/2015 06:39 AM, xschen wrote:
> I found the "intersects, intersection" calculation of postgis is very
> slow, so that I read the JTS, and found the intersects algrithem is
> this one:
>
> package com.vividsolutions.jts.geomgraph.index;
> public class SimpleEdgeSetIntersector extends EdgeSetIntersector
>
> private void computeIntersects(Edge e0, Edge e1,
> SegmentIntersector si)
> {
> com.vividsolutions.jts.geom.Coordinate pts0[] =
> e0.getCoordinates();
> com.vividsolutions.jts.geom.Coordinate pts1[] =
> e1.getCoordinates();
> for(int i0 = 0; i0 < pts0.length - 1; i0++)
> {
> for(int i1 = 0; i1 < pts1.length - 1; i1++)
> si.addIntersections(e0, i0, e1, i1);
>
> }
>
> }
>
>
> if an n points line intersects an n points line ,the complexity will
> be O(n*n).
> this algrithem wiil show very low performance, if n>10000
>
> i suggest to cut each line into sevel small pieces, group them into 4
> branch trees boxes and join, then calculate the intersects of small
> pieces in the same boxes
> so that the complexity will be O(nlog(n)).
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