in reply to
Millions of line segment intersection calcs: Looking for speed tips
You should be able to divide and conquer the data set. Rather than sorting the list by segment length, you should pick a dimension and sort on that.
Sort all the points by X and then Y. Create all the edges so that the higher X is first. Sort all the edges by X1, then X2. When processing a segment against the list, you can skip any segment where Xn1 is less than X2 or Xn2 is greater than X1. Better still, you can exit the loop early once Xn1 is less than X2 since all the rest of the segments are certain to not intersect.
The segment intersection calcs are expensive, adding a bail-out test for simple cases will go a long way by itself... but sorting the data to bail out of the entire list early should pay off handsomely as well.
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