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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