GEOS  3.8.0dev
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geos::geom::LineSegment Class Reference

#include <LineSegment.h>

Inheritance diagram for geos::geom::LineSegment:
geos::simplify::TaggedLineSegment

Public Member Functions

 LineSegment ()
 Segment 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[] (std::size_t i) const
 
Coordinateoperator[] (std::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. More...
 
bool isVertical () const
 Tests whether the segment is vertical. More...
 
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. More...
 
void reverse ()
 Reverses the direction of the line segment.
 
void normalize ()
 Puts the line segment into a normalized form. More...
 
double angle () const
 
void midPoint (Coordinate &ret) const
 Computes the midpoint of the segment. More...
 
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. More...
 
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. More...
 
double projectionFactor (const Coordinate &p) const
 Compute the projection factor for the projection of the point p onto this LineSegment. More...
 
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. More...
 
void project (const Coordinate &p, Coordinate &ret) const
 Compute the projection of a point onto the line determined by this line segment. More...
 
bool project (const LineSegment &seg, LineSegment &ret) const
 Project a line segment onto this line segment and return the resulting line segment. More...
 
void closestPoint (const Coordinate &p, Coordinate &ret) const
 Computes the closest point on this line segment to another point. More...
 
int compareTo (const LineSegment &other) const
 Compares this object with the specified object for order. More...
 
bool equalsTopo (const LineSegment &other) const
 Returns true if other is topologically equal to this LineSegment (e.g. irrespective of orientation). More...
 
CoordinateSequenceclosestPoints (const LineSegment &line)
 
CoordinateSequenceclosestPoints (const LineSegment *line)
 
bool intersection (const LineSegment &line, Coordinate &coord) const
 
bool lineIntersection (const LineSegment &line, Coordinate &ret) const
 Computes the intersection point of the lines defined by two segments, if there is one. More...
 
std::unique_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
pthe point to find the closest point to
retthe 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
pthe 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
othe 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
othera 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
coordthe 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 ret 
) 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
linea line segment defining a straight line
retwill 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
retwill 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 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
segthe 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
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 Orientation::index.

Parameters
segthe 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
Orientation::index(Coordinate, Coordinate, Coordinate)
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
segmentLengthFractionthe fraction of the segment length along the line
retwill 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
segmentLengthFractionthe fraction of the segment length along the line
offsetDistancethe distance the point is offset from the segment (positive is to the left, negative is to the right)
retwill be set to the point at that distance and offset
Exceptions
IllegalStateExceptionif the segment has zero length
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].

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
segthe line segment to project
retthe projected line segment
Returns
true if there is an overlap, false otherwise
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
pthe 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
inputPtthe point
Returns
the fraction along the line segment the projection of the point occurs
std::unique_ptr<LineString> geos::geom::LineSegment::toGeometry ( const GeometryFactory gf) const

Creates a LineString with the same coordinates as this segment

Parameters
gfthe 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: