GEOS  3.12.0dev
geos::geom::LineSegment Class Reference

`#include <LineSegment.h>`

Inheritance diagram for geos::geom::LineSegment: ## Public Member Functions

LineSegment (const Coordinate &c0, const Coordinate &c1)

LineSegment (double x0, double y0, double x1, double y1)

void setCoordinates (const Coordinate &c0, const Coordinate &c1)

void setCoordinates (const LineSegment &ls)

const Coordinateoperator[] (std::size_t i) const

Coordinateoperator[] (std::size_t i)

double getLength () const
Computes the length of the line segment.

bool isHorizontal () const

bool isVertical () const

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...

LineSegment offset (double offsetDistance)

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...

std::array< Coordinate, 2 > closestPoints (const LineSegment &line)

std::array< Coordinate, 2 > closestPoints (const LineSegment *line)

Coordinate intersection (const LineSegment &line) const

Coordinate lineIntersection (const LineSegment &line) 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

Coordinate p0

Coordinate p1
Segment start.

## Friends

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

bool operator== (const LineSegment &a, const LineSegment &b)
Checks if two LineSegment are equal (2D only check)

## 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 ?

## ◆ angle()

 double geos::geom::LineSegment::angle ( ) const
inline
Returns
the angle this segment makes with the x-axis (in radians)

References geos::geom::Coordinate::x, and geos::geom::Coordinate::y.

## ◆ closestPoint()

 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

## ◆ closestPoints()

 std::array geos::geom::LineSegment::closestPoints ( const LineSegment & line )

Computes the closest points on two line segments.

Parameters
 line the line segment to find the closest points to
Returns
a pair of Coordinates which are the closest points on the line segments.

## ◆ compareTo()

 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
 other 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

## ◆ equalsTopo()

 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.

## ◆ intersection()

 Coordinate geos::geom::LineSegment::intersection ( const LineSegment & line ) 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
Returns
intersection if found, setNull() otherwise

## ◆ isHorizontal()

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

Tests whether the segment is horizontal.

Returns
`true` if the segment is horizontal

References geos::geom::Coordinate::y.

## ◆ isVertical()

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

Tests whether the segment is vertical.

Returns
`true` if the segment is vertical

References geos::geom::Coordinate::x.

## ◆ lineIntersection()

 Coordinate geos::geom::LineSegment::lineIntersection ( const LineSegment & line ) 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
Returns
intersection if found, setNull() otherwise

## ◆ midPoint()

 void geos::geom::LineSegment::midPoint ( Coordinate & ret ) const
inline

Computes the midpoint of the segment.

Parameters
 ret will be set to the midpoint of the segment

References geos::geom::Coordinate::x, and geos::geom::Coordinate::y.

## ◆ normalize()

 void geos::geom::LineSegment::normalize ( )
inline

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.

References geos::geom::Coordinate::compareTo().

## ◆ offset()

 LineSegment geos::geom::LineSegment::offset ( double offsetDistance )

Computes the LineSegment that is offset from the segment by a given distance. The computed segment is offset to the left of the line if the offset distance is positive, to the right if negative.

Parameters
 offsetDistance the distance the point is offset from the segment (positive is to the left, negative is to the right)
Returns
a line segment offset by the specified distance
Exceptions
 IllegalStateException if the segment has zero length

## ◆ orientationIndex() [1/2]

 int geos::geom::LineSegment::orientationIndex ( const Coordinate & p ) const
inline

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

The orientation index is as defined in Orientation::index.

Parameters
 p the Coordinate 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
Orientation::index(Coordinate, Coordinate, Coordinate)

References geos::algorithm::Orientation::index().

## ◆ orientationIndex() [2/2]

 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,

• 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

## ◆ pointAlong()

 void geos::geom::LineSegment::pointAlong ( double segmentLengthFraction, Coordinate & ret ) const
inline

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

References geos::geom::Coordinate::x, and geos::geom::Coordinate::y.

## ◆ pointAlongOffset()

 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
Exceptions
 IllegalStateException if the segment has zero length

## ◆ project() [1/2]

 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].

## ◆ project() [2/2]

 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

## ◆ projectionFactor()

 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

## ◆ segmentFraction()

 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

## ◆ toGeometry()

 std::unique_ptr 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: