com.revolsys.jts.algorithm

Class RayCrossingCounter

java.lang.Object

com.revolsys.jts.algorithm.RayCrossingCounter

All Implemented Interfaces:

Visitor<LineSegment>

Direct Known Subclasses:

PointInArea

public class RayCrossingCounter
extends Object
implements Visitor<LineSegment>

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.

Author:

Martin Davis

Constructor Summary

Constructors

Constructor and Description
RayCrossingCounter(double x, double y)
RayCrossingCounter(Point point)

Method Summary

Methods

Modifier and Type	Method and Description
void	countSegment(double x1, double y1, double x2, double y2)
void	countSegment(Point p1, Point p2) For each segment, check if it crosses a horizontal ray running from the test point in the positive x direction.
void	countSegment(Segment segment)
Location	getLocation() Gets the Location of the point relative to the ring, polygon or multipolygon from which the processed segments were provided.
double	getX()
double	getY()
boolean	isOnSegment() Reports whether the point lies exactly on one of the supplied segments.
boolean	isPointInPolygon() Tests whether the point lies in or on the ring, polygon or multipolygon from which the processed segments were provided.
static Location	locatePointInRing(Point coordinates, LineString ring) Determines the Location of a point in a ring.
static Location	locatePointInRing(Point p, Point[] ring) Determines the Location of a point in a ring.
void	setPointOnSegment(boolean pointOnSegment)
boolean	visit(LineSegment segment) Visit an item of type T, performing some operation on the item.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

RayCrossingCounter

public RayCrossingCounter(double x,
                  double y)

RayCrossingCounter

public RayCrossingCounter(Point point)

Method Detail

locatePointInRing

public static Location locatePointInRing(Point coordinates,
                         LineString 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

locatePointInRing

public static Location locatePointInRing(Point p,
                         Point[] 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 Point forming a ring

Returns:

the location of the point in the ring

countSegment

public void countSegment(double x1,
                double y1,
                double x2,
                double y2)

countSegment

public void countSegment(Point p1,
                Point p2)

For each segment, check if it crosses a horizontal ray running from the test point in the positive x direction.

Parameters:

p1 - an endpoint of the segment

p2 - another endpoint of the segment

countSegment

public void countSegment(Segment segment)

getLocation

public Location 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

getX

public double getX()

getY

public double getY()

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

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

setPointOnSegment

public void setPointOnSegment(boolean pointOnSegment)

visit

public boolean visit(LineSegment segment)

Description copied from interface: Visitor

Visit an item of type T, performing some operation on the item. The method must return true if further items are to be processed or false if no further items are to be processed.

Specified by:

visit in interface Visitor<LineSegment>

Parameters:

segment - The item to process.

Returns:

True if further items are to be processed, false otherwise.