GEOS
3.9.0dev

Functions to compute the orientation of basic geometric structures including point triplets (triangles) and rings. More...
#include <Orientation.h>
Public Types  
enum  { CLOCKWISE = 1, COLLINEAR = 0, COUNTERCLOCKWISE = 1, RIGHT = 1, LEFT = 1, STRAIGHT = 0 } 
Static Public Member Functions  
static int  index (const geom::Coordinate &p1, const geom::Coordinate &p2, const geom::Coordinate &q) 
Returns the orientation index of the direction of the point q relative to a directed infinite line specified by p1p2. More...  
static bool  isCCW (const geom::CoordinateSequence *ring) 
Functions to compute the orientation of basic geometric structures including point triplets (triangles) and rings.
Orientation is a fundamental property of planar geometries (and more generally geometry on twodimensional manifolds).
Orientation is notoriously subject to numerical precision errors in the case of collinear or nearly collinear points. JTS uses extendedprecision arithmetic to increase the robustness of the computation.

static 
Returns the orientation index of the direction of the point q relative to a directed infinite line specified by p1p2.
The index indicates whether the point lies to the Orientation::LEFT
or Orientation::RIGHT
of the line, or lies on it Orientation::COLLINEAR
. The index also indicates the orientation of the triangle formed by the three points ( Orientation::COUNTERCLOCKWISE
, Orientation::CLOCKWISE
, or Orientation::STRAIGHT
)

static 
Computes whether a ring defined by a geom::CoordinateSequence is oriented counterclockwise.
This algorithm is guaranteed to work with valid rings. It also works with "mildly invalid" rings which contain collapsed (coincident) flat segments along the top of the ring. If the ring is "more" invalid (e.g. selfcrosses or touches), the computed result may not be correct.
ring  a CoordinateSequence forming a ring (with first and last point identical) 
IllegalArgumentException  if there are too few points to determine orientation (< 4) 