GEOS  3.9.0dev
geos::algorithm::CGAlgorithmsDD Class Reference

Implements basic computational geometry algorithms using extended precision float-point arithmetic. More...

`#include <CGAlgorithmsDD.h>`

## Public Types

enum  { CLOCKWISE = -1, COLLINEAR = 0, COUNTERCLOCKWISE = 1 }

enum  { RIGHT = -1, LEFT = 1, STRAIGHT = 0, FAILURE = 2 }

## Static Public Member Functions

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...

static int orientationIndexFilter (const geom::Coordinate &pa, const geom::Coordinate &pb, const geom::Coordinate &pc)
A filter for computing the orientation index of three coordinates. More...

static int orientation (double x)

static geom::Coordinate intersection (const geom::Coordinate &p1, const geom::Coordinate &p2, const geom::Coordinate &q1, const geom::Coordinate &q2)

static int signOfDet2x2 (double dx1, double dy1, double dx2, double dy2)

static DD detDD (double x1, double y1, double x2, double y2)

static DD detDD (const DD &x1, const DD &y1, const DD &x2, const DD &y2)

static geom::Coordinate circumcentreDD (const geom::Coordinate &a, const geom::Coordinate &b, const geom::Coordinate &c)
Computes the circumcentre of a triangle. More...

## Static Protected Member Functions

static int signOfDet2x2 (const DD &x1, const DD &y1, const DD &x2, const DD &y2)

## Detailed Description

Implements basic computational geometry algorithms using extended precision float-point arithmetic.

## Member Function Documentation

 static geom::Coordinate geos::algorithm::CGAlgorithmsDD::circumcentreDD ( const geom::Coordinate & a, const geom::Coordinate & b, const geom::Coordinate & c )
static

Computes the circumcentre of a triangle.

The circumcentre is the centre of the circumcircle, the smallest circle which encloses the triangle. It is also the common intersection point of the perpendicular bisectors of the sides of the triangle, and is the only point which has equal distance to all three vertices of the triangle.

The circumcentre does not necessarily lie within the triangle. For example, the circumcentre of an obtuse isosceles triangle lies outside the triangle.

This method uses DD extended-precision arithmetic to provide more accurate results than geos::geom::Triangle::circumcentre(const Coordinate& p0, const Coordinate& p1, const Coordinate& p2 "circumcentre(Coordinate, Coordinate, Coordinate)").

Parameters
 a a vertex of the triangle b a vertex of the triangle c a vertex of the triangle
Returns
the circumcentre of the triangle
 static geom::Coordinate geos::algorithm::CGAlgorithmsDD::intersection ( const geom::Coordinate & p1, const geom::Coordinate & p2, const geom::Coordinate & q1, const geom::Coordinate & q2 )
static

If the lines are parallel (either identical or separate) a null value is returned.

Parameters
 p1 an endpoint of line segment 1 p2 an endpoint of line segment 1 q1 an endpoint of line segment 2 q2 an endpoint of line segment 2
Returns
an intersection point if one exists, or null if the lines are parallel
 static int geos::algorithm::CGAlgorithmsDD::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
 static int geos::algorithm::CGAlgorithmsDD::orientationIndexFilter ( const geom::Coordinate & pa, const geom::Coordinate & pb, const geom::Coordinate & pc )
static

A filter for computing the orientation index of three coordinates.

If the orientation can be computed safely using standard DP arithmetic, this routine returns the orientation index. Otherwise, a value `i > 1` is returned. In this case the orientation index must be computed using some other more robust method.

The filter is fast to compute, so can be used to avoid the use of slower robust methods except when they are really needed, thus providing better average performance.

Uses an approach due to Jonathan Shewchuk, which is in the public domain.

Parameters
 pa a coordinate pb a coordinate pc a coordinate
Returns
the orientation index if it can be computed safely
`i > 1` if the orientation index cannot be computed safely

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