} // public override bool IsCCW(Coordinates ring)
/// <summary>
/// This algorithm does not attempt to first check the point against the envelope
/// of the ring.
/// </summary>
/// <param name="p"></param>
/// <param name="ring">Assumed to have first point identical to last point</param>
/// <returns></returns>
public override bool IsPointInRing(Coordinate p, Coordinates ring)
{
int i;
int i1; // point index; i1 = i-1
double xInt; // x intersection of segment with ray
int crossings = 0; // number of segment/ray crossings
double x1; // translated coordinates
double y1;
double x2;
double y2;
int nPts = ring.Count;
//
// For each segment l = (i-1, i), see if it crosses ray from test point in positive x direction.
//
for (i = 1; i < nPts; i++)
{
i1 = i - 1;
Coordinate p1 = ring[i];
Coordinate p2 = ring[i1];
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.SignOfDet2x2(x1, y1, x2, y2) / (y2 - y1);
//xsave = xInt;
//
// crosses ray if strictly positive intersection.
//
if (0.0 < xInt)
{
crossings++;
}
}
}
//
// p is inside if number of crossings is odd.
//
if ((crossings % 2) == 1)
{
return(true);
}
else
{
return(false);
}
} // public override bool IsPointInPolygon(Coordinate p, Coordinates ring)
public static int OrientationIndex(Coordinate p1, Coordinate p2, Coordinate 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.SignOfDet2x2(dx1, dy1, dx2, dy2));
} // public static int OrientationIndex(Coordinate p1, Coordinate p2, Coordinate q)
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.SignOfDet2x2(x1, y1, x2, y2) / (y2 - y1);
//xsave = xInt;
//
// crosses ray if strictly positive intersection.
//
if (0.0 < xInt)
{
_crossings++;
}
}
}
