index static method
Returns the orientation index of the direction of the point q relative to
a directed infinite line specified by p1-p2.
The index indicates whether the point lies to the {@link #LEFT} or {@link #RIGHT}
of the line, or lies on it {@link #COLLINEAR}.
The index also indicates the orientation of the triangle formed by the three points
( {@link #COUNTERCLOCKWISE}, {@link #CLOCKWISE}, or {@link #STRAIGHT} )
@param p1 the origin point of the line vector @param p2 the final point of the line vector @param q the point to compute the direction to
@return -1 ( {@link #CLOCKWISE} or {@link #RIGHT} ) if q is clockwise (right) from p1-p2; 1 ( {@link #COUNTERCLOCKWISE} or {@link #LEFT} ) if q is counter-clockwise (left) from p1-p2; 0 ( {@link #COLLINEAR} or {@link #STRAIGHT} ) if q is collinear with p1-p2
Implementation
static int index(Coordinate p1, Coordinate p2, Coordinate q) {
/*
* MD - 9 Aug 2010 It seems that the basic algorithm is slightly orientation
* dependent, when computing the orientation of a point very close to a
* line. This is possibly due to the arithmetic in the translation to the
* origin.
*
* For instance, the following situation produces identical results in spite
* of the inverse orientation of the line segment:
*
* Coordinate p0 = new Coordinate(219.3649559090992, 140.84159161824724);
* Coordinate p1 = new Coordinate(168.9018919682399, -5.713787599646864);
*
* Coordinate p = new Coordinate(186.80814046338352, 46.28973405831556); int
* orient = orientationIndex(p0, p1, p); int orientInv =
* orientationIndex(p1, p0, p);
*
* A way to force consistent results is to normalize the orientation of the
* vector using the following code. However, this may make the results of
* orientationIndex inconsistent through the triangle of points, so it's not
* clear this is an appropriate patch.
*
*/
return CGAlgorithmsDD.orientationIndex(p1, p2, q);
// testing only
//return ShewchuksDeterminant.orientationIndex(p1, p2, q);
// previous implementation - not quite fully robust
//return RobustDeterminant.orientationIndex(p1, p2, q);
}