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geos::geom::LineSegment Class Reference

#include <LineSegment.h>

Inheritance diagram for geos::geom::LineSegment:

geos::simplify::TaggedLineSegment List of all members.

Public Member Functions

 LineSegment ()
 Segemnt end.
 LineSegment (const LineSegment &ls)
 LineSegment (const Coordinate &c0, const Coordinate &c1)
 Constructs a LineSegment with the given start and end Coordinates.
 LineSegment (double x0, double y0, double x1, double y1)
void setCoordinates (const Coordinate &c0, const Coordinate &c1)
const Coordinateoperator[] (size_t i) const
Coordinateoperator[] (size_t i)
void setCoordinates (const LineSegment &ls)
double getLength () const
 Computes the length of the line segment.
bool isHorizontal () const
 Tests whether the segment is horizontal.
bool isVertical () const
 Tests whether the segment is vertical.
int orientationIndex (const LineSegment &seg) const
int orientationIndex (const LineSegment *seg) const
int orientationIndex (const Coordinate &p) const
 Determines the orientation index of a Coordinate relative to this segment.
void reverse ()
 Reverses the direction of the line segment.
void normalize ()
 Puts the line segment into a normalized form.
double angle () const
void midPoint (Coordinate &ret) const
 Computes the midpoint of the segment.
double distance (const LineSegment &ls) const
 Computes the distance between this line segment and another one.
double distance (const Coordinate &p) const
 Computes the distance between this line segment and a point.
double distancePerpendicular (const Coordinate &p) const
 Computes the perpendicular distance between the (infinite) line defined by this line segment and a point.
void pointAlong (double segmentLengthFraction, Coordinate &ret) const
 Computes the Coordinate that lies a given fraction along the line defined by this segment.
void pointAlongOffset (double segmentLengthFraction, double offsetDistance, Coordinate &ret) const
 Computes the Coordinate that lies a given fraction along the line defined by this segment and offset from the segment by a given distance.
double projectionFactor (const Coordinate &p) const
 Compute the projection factor for the projection of the point p onto this LineSegment.
double segmentFraction (const Coordinate &inputPt) const
 Computes the fraction of distance (in [0.0, 1.0]) that the projection of a point occurs along this line segment.
void project (const Coordinate &p, Coordinate &ret) const
 Compute the projection of a point onto the line determined by this line segment.
bool project (const LineSegment &seg, LineSegment &ret) const
 Project a line segment onto this line segment and return the resulting line segment.
void closestPoint (const Coordinate &p, Coordinate &ret) const
 Computes the closest point on this line segment to another point.
int compareTo (const LineSegment &other) const
 Compares this object with the specified object for order.
bool equalsTopo (const LineSegment &other) const
 Returns true if other is topologically equal to this LineSegment (e.g. irrespective of orientation).
CoordinateSequenceclosestPoints (const LineSegment &line)
CoordinateSequenceclosestPoints (const LineSegment *line)
bool intersection (const LineSegment &line, Coordinate &coord) const
bool lineIntersection (const LineSegment &line, Coordinate &coord) const
 Computes the intersection point of the lines defined by two segments, if there is one.
std::auto_ptr< LineStringtoGeometry (const GeometryFactory &gf) const

Public Attributes

Coordinate p0
Coordinate p1
 Segment start.

Friends

std::ostream & operator<< (std::ostream &o, const LineSegment &l)

Detailed Description

Represents a line segment defined by two Coordinate. Provides methods to compute various geometric properties and relationships of line segments.

This class is designed to be easily mutable (to the extent of having its contained points public). This supports a common pattern of reusing a single LineSegment object as a way of computing segment properties on the segments defined by arrays or lists of Coordinates.

TODO: have this class keep pointers rather then real Coordinates ?


Member Function Documentation

double geos::geom::LineSegment::angle  )  const
 

Returns:
the angle this segment makes with the x-axis (in radians)

void geos::geom::LineSegment::closestPoint const Coordinate p,
Coordinate ret
const
 

Computes the closest point on this line segment to another point.

Parameters:
p the point to find the closest point to
ret the Coordinate to which the closest point on the line segment to the point p will be written

CoordinateSequence* geos::geom::LineSegment::closestPoints const LineSegment line  ) 
 

Computes the closest points on two line segments.

Parameters:
p the point to find the closest point to
Returns:
a pair of Coordinates which are the closest points on the line segments. The returned CoordinateSequence must be deleted by caller

int geos::geom::LineSegment::compareTo const LineSegment other  )  const
 

Compares this object with the specified object for order.

Uses the standard lexicographic ordering for the points in the LineSegment.

Parameters:
o the LineSegment with which this LineSegment is being compared
Returns:
a negative integer, zero, or a positive integer as this LineSegment is less than, equal to, or greater than the specified LineSegment

bool geos::geom::LineSegment::equalsTopo const LineSegment other  )  const
 

Returns true if other is topologically equal to this LineSegment (e.g. irrespective of orientation).

Parameters:
other a LineSegment with which to do the comparison.
Returns:
true if other is a LineSegment with the same values for the x and y ordinates.

bool geos::geom::LineSegment::intersection const LineSegment line,
Coordinate coord
const
 

Computes an intersection point between two segments, if there is one. There may be 0, 1 or many intersection points between two segments. If there are 0, null is returned. If there is 1 or more, a single one is returned (chosen at the discretion of the algorithm). If more information is required about the details of the intersection, the LineIntersector class should be used.

Parameters:
line 
coord the Coordinate to write the result into
Returns:
true if an intersection was found, false otherwise

bool geos::geom::LineSegment::isHorizontal  )  const
 

Tests whether the segment is horizontal.

Returns:
true if the segment is horizontal

bool geos::geom::LineSegment::isVertical  )  const
 

Tests whether the segment is vertical.

Returns:
true if the segment is vertical

bool geos::geom::LineSegment::lineIntersection const LineSegment line,
Coordinate coord
const
 

Computes the intersection point of the lines defined by two segments, if there is one.

There may be 0, 1 or an infinite number of intersection points between two lines. If there is a unique intersection point, it is returned. Otherwise, null is returned. If more information is required about the details of the intersection, the algorithms::LineIntersector class should be used.

Parameters:
line a line segment defining a straight line
ret will be set to the intersection point (if any)
Returns:
true if an intersection was found, false otherwise

void geos::geom::LineSegment::midPoint Coordinate ret  )  const
 

Computes the midpoint of the segment.

Parameters:
ret will be set to the midpoint of the segment

void geos::geom::LineSegment::normalize  ) 
 

Puts the line segment into a normalized form.

This is useful for using line segments in maps and indexes when topological equality rather than exact equality is desired.

int geos::geom::LineSegment::orientationIndex const Coordinate p  )  const
 

Determines the orientation index of a Coordinate relative to this segment.

The orientation index is as defined in CGAlgorithms::computeOrientation.

Parameters:
seg the LineSegment to compare
Returns:
1 if p is to the left of this segment

-1 if p is to the right of this segment

0 if p is collinear with this segment

See also:
CGAlgorithms::computeOrientation(Coordinate, Coordinate, Coordinate)

int geos::geom::LineSegment::orientationIndex const LineSegment seg  )  const
 

Determines the orientation of a LineSegment relative to this segment. The concept of orientation is specified as follows: Given two line segments A and L, <ul A is to the left of a segment L if A lies wholly in the closed half-plane lying to the left of L A is to the right of a segment L if A lies wholly in the closed half-plane lying to the right of L otherwise, A has indeterminate orientation relative to L. This happens if A is collinear with L or if A crosses the line determined by L.

Parameters:
seg the LineSegment to compare
Returns:
1 if seg is to the left of this segment

-1 if seg is to the right of this segment

0 if seg has indeterminate orientation relative to this segment

void geos::geom::LineSegment::pointAlong double  segmentLengthFraction,
Coordinate ret
const
 

Computes the Coordinate that lies a given fraction along the line defined by this segment.

A fraction of 0.0 returns the start point of the segment; a fraction of 1.0 returns the end point of the segment. If the fraction is < 0.0 or > 1.0 the point returned will lie before the start or beyond the end of the segment.

Parameters:
segmentLengthFraction the fraction of the segment length along the line
ret will be set to the point at that distance

void geos::geom::LineSegment::pointAlongOffset double  segmentLengthFraction,
double  offsetDistance,
Coordinate ret
const
 

Computes the Coordinate that lies a given fraction along the line defined by this segment and offset from the segment by a given distance.

A fraction of 0.0 offsets from the start point of the segment; a fraction of 1.0 offsets from the end point of the segment.

The computed point is offset to the left of the line if the offset distance is positive, to the right if negative.

Parameters:
segmentLengthFraction the fraction of the segment length along the line
offsetDistance the distance the point is offset from the segment (positive is to the left, negative is to the right)
ret will be set to the point at that distance and offset

bool geos::geom::LineSegment::project const LineSegment seg,
LineSegment ret
const
 

Project a line segment onto this line segment and return the resulting line segment.

The returned line segment will be a subset of the target line line segment. This subset may be null, if the segments are oriented in such a way that there is no projection.

Note that the returned line may have zero length (i.e. the same endpoints). This can happen for instance if the lines are perpendicular to one another.

Parameters:
seg the line segment to project
ret the projected line segment
Returns:
true if there is an overlap, false otherwise

void geos::geom::LineSegment::project const Coordinate p,
Coordinate ret
const
 

Compute the projection of a point onto the line determined by this line segment.

Note that the projected point may lie outside the line segment. If this is the case, the projection factor will lie outside the range [0.0, 1.0].

double geos::geom::LineSegment::projectionFactor const Coordinate p  )  const
 

Compute the projection factor for the projection of the point p onto this LineSegment.

The projection factor is the constant r by which the vector for this segment must be multiplied to equal the vector for the projection of p on the line defined by this segment.

The projection factor returned will be in the range (-inf, +inf)

Parameters:
p the point to compute the factor for
Returns:
the projection factor for the point

double geos::geom::LineSegment::segmentFraction const Coordinate inputPt  )  const
 

Computes the fraction of distance (in [0.0, 1.0]) that the projection of a point occurs along this line segment.

If the point is beyond either ends of the line segment, the closest fractional value (0.0 or 1.0) is returned.

Essentially, this is the projectionFactor clamped to the range [0.0, 1.0].

Parameters:
inputPt the point
Returns:
the fraction along the line segment the projection of the point occurs

std::auto_ptr<LineString> geos::geom::LineSegment::toGeometry const GeometryFactory gf  )  const
 

Creates a LineString with the same coordinates as this segment

Parameters:
gf the geometery factory to use
Returns:
a LineString with the same geometry as this segment


The documentation for this class was generated from the following file:
Generated on Thu Jun 11 06:17:02 2009 for GEOS by  doxygen 1.4.4