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.
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
void reverse ()
 Reverses the direction of the line segment.
void normalize ()
 Puts the line segment into a normalized form.
double angle () const
 
Returns:
the angle this segment makes with the x-axis (in radians)

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.
double projectionFactor (const Coordinate &p) const
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

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

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

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::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.

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 k by which the vector for this segment must be multiplied to equal the vector for the projection of p.

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

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

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.

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

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


The documentation for this class was generated from the following file:
Generated on Fri Mar 27 04:53:26 2009 for GEOS by  doxygen 1.5.4