object RayCrossingCounter

Counts the number of segments crossed by a horizontal ray extending to the right from a given point, in an incremental fashion. This can be used to determine whether a point lies in a {link Polygonal} geometry. The class determines the situation where the point lies exactly on a segment. When being used for Point-In-Polygon determination, this case allows short-circuiting the evaluation.

This class handles polygonal geometries with any number of shells and holes. The orientation of the shell and hole rings is unimportant. In order to compute a correct location for a given polygonal geometry, it is essential that all segments are counted which

  • touch the ray
  • lie in in any ring which may contain the point

The only exception is when the point-on-segment situation is detected, in which case no further processing is required. The implication of the above rule is that segments which can be a priori determined to not touch the ray (i.e. by a test of their bounding box or Y-extent) do not need to be counted. This allows for optimization by indexing.

This implementation uses the extended-precision orientation test, to provide maximum robustness and consistency within other algorithms.

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  12. def locatePointInRing(p: Coordinate, ring: CoordinateSequence): Int

    Determines the {link Location} of a point in a ring.

    Determines the {link Location} of a point in a ring.

    p

    the point to test

    ring

    a coordinate sequence forming a ring return the location of the point in the ring

  13. def locatePointInRing(p: Coordinate, ring: Array[Coordinate]): Int

    Determines the {link Location} of a point in a ring.

    Determines the {link Location} of a point in a ring. This method is an exemplar of how to use this class.

    p

    the point to test

    ring

    an array of Coordinates forming a ring return the location of the point in the ring

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