/// <summary>
/// Returns the orientation index of the direction of the point <paramref name="q"/> relative to
/// a directed infinite line specified by <c>p1->p2</c>.
/// The index indicates whether the point lies to the <see cref="OrientationIndex.Left"/>
/// or <see cref="OrientationIndex.Right"/> of the line, or lies on it <see cref="OrientationIndex.Collinear"/>.
/// The index also indicates the orientation of the triangle formed by the three points
/// (<see cref="OrientationIndex.CounterClockwise"/>, <see cref="OrientationIndex.Clockwise"/>, or
/// <see cref="OrientationIndex.Straight"/> )
/// </summary>
/// <param name="p1">The origin point of the line vector</param>
/// <param name="p2">The final point of the line vector</param>
/// <param name="q">The point to compute the direction to</param>
/// <returns>
/// The <see cref="OrientationIndex"/> of q in regard to the vector <c>p1->p2</c>
/// <list type="Table">
/// <listheader>
/// <term>Value</term><description>Description</description>
/// </listheader>
/// <item>
/// <term><see cref="OrientationIndex.Collinear"/>, <see cref="OrientationIndex.Straight"/></term>
/// <description><paramref name="q"/> is collinear with <c>p1->p2</c></description>
/// </item>
/// <item>
/// <term><see cref="OrientationIndex.Clockwise"/>, <see cref="OrientationIndex.Right"/></term>
/// <description><paramref name="q"/> is clockwise (right) from <c>p1->p2</c></description>
/// </item>
/// <item>
/// <term><see cref="OrientationIndex.CounterClockwise"/>, <see cref="OrientationIndex.Left"/></term>
/// <description><paramref name="q"/> is counter-clockwise (left) from <c>p1->p2</c></description>
/// </item>
/// </list>
/// </returns>
public static OrientationIndex 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.
*
*/
var res = (OrientationIndex)CGAlgorithmsDD.OrientationIndex(p1, p2, q);
return(res); //(Orientation)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);
}
private void CheckDD(Coordinate p1, Coordinate p2, Coordinate q1,
Coordinate q2, Coordinate intPt)
{
var intPtDD = CGAlgorithmsDD.Intersection(p1, p2, q1, q2);
bool isIn = IsInSegmentEnvelopes(intPtDD);
Debug.WriteLine("DD in env = " + isIn + " --------------------- " + intPtDD);
double distance = intPt.Distance(intPtDD);
if (distance > 0.0001)
{
Debug.WriteLine("Distance = " + distance);
}
}