Class RayCrossingCounter

Hierarchy: Object , RayCrossingCounter

public class 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 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.

Authors:: Martin Davis

public RayCrossingCounter(Coordinate p)

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 - p the point to test; ring - ring an array of Coordinates forming a ring

Returns:: the location of the point in the ring

public static int locatePointInRing(Coordinate p, CoordinateSequence ring)

Determines the Location of a point in a ring.

Parameters:: p - p the point to test; ring - ring a coordinate sequence forming a ring

Returns:: the location of the point in the ring

public void countSegment(Coordinate p1, Coordinate p2)

Counts a segment

Parameters:: p1 - p1 an endpoint of the segment; p2 - p2 another endpoint of the segment

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

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

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