/// <summary>
/// Returns the index of the direction of the point q
/// relative to a
/// vector specified by p1-p2.
///
/// </summary>
/// <param name="p1">the origin point of the vector
/// </param>
/// <param name="p2">the final point of the vector
/// </param>
/// <param name="q">the point to compute the direction to
///
/// </param>
/// <returns> 1 if q is counter-clockwise (left) from p1-p2
/// </returns>
/// <returns> -1 if q is clockwise (right) from p1-p2
/// </returns>
/// <returns> 0 if q is collinear with p1-p2
/// </returns>
public static int OrientationIndex(Coordinate p1, Coordinate p2, Coordinate q)
{
if (p1 == null)
{
throw new ArgumentNullException("p1");
}
if (p2 == null)
{
throw new ArgumentNullException("p2");
}
if (q == null)
{
throw new ArgumentNullException("q");
}
// travelling along p1->p2, turn counter clockwise to get to q return 1,
// travelling along p1->p2, turn clockwise to get to q return -1,
// p1, p2 and q are colinear return 0.
double dx1 = p2.X - p1.X;
double dy1 = p2.Y - p1.Y;
double dx2 = q.X - p2.X;
double dy2 = q.Y - p2.Y;
return(RobustDeterminant.SignOfDeterminant(dx1, dy1, dx2, dy2));
}
private void TestLineSegment(Coordinate p, LineSegment seg)
{
double xInt; // x intersection of segment with ray
double x1; // translated coordinates
double y1;
double x2;
double y2;
// Test if segment Crosses ray from test point in positive x direction.
Coordinate p1 = seg.p0;
Coordinate p2 = seg.p1;
x1 = p1.X - p.X;
y1 = p1.Y - p.Y;
x2 = p2.X - p.X;
y2 = p2.Y - p.Y;
if (((y1 > 0) && (y2 <= 0)) || ((y2 > 0) && (y1 <= 0)))
{
// segment straddles x axis, so compute intersection.
xInt = RobustDeterminant.SignOfDeterminant(x1, y1, x2, y2) / (y2 - y1);
//xsave = xInt;
// Crosses ray if strictly positive intersection.
if (0.0 < xInt)
{
crossings++;
}
}
}
/// <summary>
/// This algorithm does not attempt to first check the point against the envelope
/// of the ring.
///
/// </summary>
/// <param name="ring">assumed to have first point identical to last point
/// </param>
public bool IsPointInRing(Coordinate p, ICoordinateList ring)
{
if (p == null)
{
throw new ArgumentNullException("p");
}
if (ring == null)
{
throw new ArgumentNullException("ring");
}
/*
* For each segment l = (i-1, i), see if it crosses ray from test point in positive x direction.
*/
int crossings = 0; // number of segment/ray crossings
int nCount = ring.Count;
for (int i = 1; i < nCount; i++)
{
int i1 = i - 1;
Coordinate p1 = ring[i];
Coordinate p2 = ring[i1];
if (((p1.Y > p.Y) && (p2.Y <= p.Y)) ||
((p2.Y > p.Y) && (p1.Y <= p.Y)))
{
double x1 = p1.X - p.X;
double y1 = p1.Y - p.Y;
double x2 = p2.X - p.X;
double y2 = p2.Y - p.Y;
/*
* segment straddles x axis, so compute intersection with x-axis.
*/
double xInt = RobustDeterminant.SignOfDeterminant(x1, y1, x2, y2) / (y2 - y1);
//xsave = xInt;
/*
* crosses ray if strictly positive intersection.
*/
if (xInt > 0.0)
{
crossings++;
}
}
}
/*
* p is inside if number of crossings is odd.
*/
if ((crossings % 2) == 1)
{
return(true);
}
else
{
return(false);
}
}