com.vividsolutions.jts.algorithm

Class 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.

    • Constructor Detail

      • RayCrossingCounter

        public RayCrossingCounter(Coordinate p)

    • Method Detail

      • 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

      • countSegment

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

      • 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