[aprssig] filtering using shape files
Steve Dimse steve at dimse.comSat Mar 10 22:12:08 UTC 2007
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On Mar 10, 2007, at 4:51 PM, Scott Miller wrote: > I think you'd need to find a different solution for stream processing, > though. > The algorithm is well known and it is easy to find code examples on the internet. Distilled, the idea is to draw an imaginary line segment between the point under test and an arbitrary distant point (known to be outside the shape, e.g. the north pole), then check mathematically to see if that imaginary line crosses each of the line segments in the polygon under test. If the number of crossings is odd, the point lies within the polygon. If the number of intersections is zero or even, the point lies outside the polygon. Steve K4HG
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