GEOS  3.8.0dev
geos::algorithm::RayCrossingCounter Class Reference

Counts the number of segments crossed by a horizontal ray extending to the right from a given point, in an incremental fashion. More...

`#include <RayCrossingCounter.h>`

## Public Member Functions

RayCrossingCounter (const geom::Coordinate &p_point)

void countSegment (const geom::Coordinate &p1, const geom::Coordinate &p2)

bool isOnSegment ()

int getLocation ()

bool isPointInPolygon ()

## Static Public Member Functions

static int locatePointInRing (const geom::Coordinate &p, const geom::CoordinateSequence &ring)

static int locatePointInRing (const geom::Coordinate &p, const std::vector< const geom::Coordinate * > &ring)
Semantically equal to the above, just different args encoding.

static int orientationIndex (const geom::Coordinate &p1, const geom::Coordinate &p2, const geom::Coordinate &q)
Returns the index of the direction of the point `q` relative to a vector specified by `p1-p2`. More...

## Detailed Description

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.

## Member Function Documentation

 void geos::algorithm::RayCrossingCounter::countSegment ( const geom::Coordinate & p1, const geom::Coordinate & p2 )

Counts a segment

Parameters
 p1 an endpoint of the segment p2 another endpoint of the segment
 int geos::algorithm::RayCrossingCounter::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
 bool geos::algorithm::RayCrossingCounter::isOnSegment ( )
inline

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
 bool geos::algorithm::RayCrossingCounter::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
 static int geos::algorithm::RayCrossingCounter::locatePointInRing ( const geom::Coordinate & p, const geom::CoordinateSequence & ring )
static

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
 static int geos::algorithm::RayCrossingCounter::orientationIndex ( const geom::Coordinate & p1, const geom::Coordinate & p2, const geom::Coordinate & q )
static

Returns the index of the direction of the point `q` relative to a vector specified by `p1-p2`.

Parameters
 p1 the origin point of the vector p2 the final point of the vector q the point to compute the direction to
Returns
1 if q is counter-clockwise (left) from p1-p2
-1 if q is clockwise (right) from p1-p2
0 if q is collinear with p1-p2

The documentation for this class was generated from the following file: