Class RayCrossingCounter

java.lang.Object
org.locationtech.jts.algorithm.RayCrossingCounter
public class RayCrossingCounter extends Object
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 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.

Author:
Martin Davis

  • Constructor Details

    • RayCrossingCounter

      public RayCrossingCounter(Coordinate p)

  • Method Details

    • locatePointInRing

      public static int locatePointInRing(Coordinate p, Coordinate[] ring)
      Determines the Location of a point in a ring. This method is an exemplar of how to use this class.
      Parameters:
      p - the point to test
      ring - an array of Coordinates forming a ring
      Returns:
      the location of the point in the ring

    • locatePointInRing

      public static int locatePointInRing(Coordinate p, CoordinateSequence ring)
      Determines the Location of a point in a ring.
      Parameters:
      p - the point to test
      ring - a coordinate sequence forming a ring
      Returns:
      the location of the point in the ring

    • countSegment

      public void countSegment(Coordinate p1, Coordinate p2)
      Counts a segment
      Parameters:
      p1 - an endpoint of the segment
      p2 - another endpoint of the segment

    • getCount

      public int getCount()
      Gets the count of crossings.
      Returns:
      the crossing count

    • isOnSegment

      public boolean isOnSegment()
      Reports whether the point lies exactly on one of the supplied segments. This method may be called at any time as segments are processed. If the result of this method is true, no further segments need be supplied, since the result will never change again.
      Returns:
      true if the point lies exactly on a segment

    • getLocation

      public int getLocation()
      Gets the Location of the point relative to the ring, polygon or multipolygon from which the processed segments were provided.

      This method only determines the correct location if all relevant segments must have been processed.

      Returns:
      the Location of the point

    • isPointInPolygon

      public boolean isPointInPolygon()
      Tests whether the point lies in or on the ring, polygon or multipolygon from which the processed segments were provided.

      This method only determines the correct location if all relevant segments must have been processed.

      Returns:
      true if the point lies in or on the supplied polygon