/// <summary>
///
/// </summary>
/// <param name="c"></param>
/// <returns></returns>
private Stack <ICoordinate> GrahamScan(ICoordinate[] c)
{
ICoordinate p;
Stack <ICoordinate> ps = new Stack <ICoordinate>(c.Length);
ps.Push(c[0]);
ps.Push(c[1]);
ps.Push(c[2]);
for (int i = 3; i < c.Length; i++)
{
p = ps.Pop();
while (CGAlgorithms.ComputeOrientation(ps.Peek(), p, c[i]) > 0)
{
p = ps.Pop();
}
ps.Push(p);
ps.Push(c[i]);
}
ps.Push(c[0]);
return(ps);
}
/// <summary>
///
/// </summary>
/// <param name="p"></param>
/// <param name="poly"></param>
/// <returns></returns>
public static bool ContainsPointInPolygon(ICoordinate p, IPolygon poly)
{
if (poly.IsEmpty)
{
return(false);
}
ILinearRing shell = (ILinearRing)poly.ExteriorRing;
if (!CGAlgorithms.IsPointInRing(p, shell.Coordinates))
{
return(false);
}
// now test if the point lies in or on the holes
for (int i = 0; i < poly.NumInteriorRings; i++)
{
ILinearRing hole = (ILinearRing)poly.GetInteriorRingN(i);
if (CGAlgorithms.IsPointInRing(p, hole.Coordinates))
{
return(false);
}
}
return(true);
}
/// <summary>
/// Uses a heuristic to reduce the number of points scanned to compute the hull.
/// The heuristic is to find a polygon guaranteed to
/// be in (or on) the hull, and eliminate all points inside it.
/// A quadrilateral defined by the extremal points
/// in the four orthogonal directions
/// can be used, but even more inclusive is
/// to use an octilateral defined by the points in the 8 cardinal directions.
/// Note that even if the method used to determine the polygon vertices
/// is not 100% robust, this does not affect the robustness of the convex hull.
/// </summary>
/// <param name="pts"></param>
/// <returns></returns>
private ICoordinate[] Reduce(ICoordinate[] pts)
{
ICoordinate[] polyPts = ComputeOctRing(inputPts);
// unable to compute interior polygon for some reason
if (polyPts == null)
{
return(inputPts);
}
// add points defining polygon
SortedSet <ICoordinate> reducedSet = new SortedSet <ICoordinate>();
for (int i = 0; i < polyPts.Length; i++)
{
reducedSet.Add(polyPts[i]);
}
/*
* Add all unique points not in the interior poly.
* CGAlgorithms.IsPointInRing is not defined for points actually on the ring,
* but this doesn't matter since the points of the interior polygon
* are forced to be in the reduced set.
*/
for (int i = 0; i < inputPts.Length; i++)
{
if (!CGAlgorithms.IsPointInRing(inputPts[i], polyPts))
{
reducedSet.Add(inputPts[i]);
}
}
ICoordinate[] arr = new ICoordinate[reducedSet.Count];
reducedSet.CopyTo(arr, 0);
return(arr);
}
/// <summary>
///
/// </summary>
/// <param name="pt"></param>
/// <returns></returns>
public bool IsInside(ICoordinate pt)
{
return(CGAlgorithms.IsPointInRing(pt, pts));
}
/// <summary>
///
/// </summary>
/// <param name="p1"></param>
/// <param name="p2"></param>
/// <param name="q1"></param>
/// <param name="q2"></param>
/// <returns></returns>
public override int ComputeIntersect(ICoordinate p1, ICoordinate p2, ICoordinate q1, ICoordinate q2)
{
isProper = false;
// first try a fast test to see if the envelopes of the lines intersect
if (!Envelope.Intersects(p1, p2, q1, q2))
{
return(DontIntersect);
}
// for each endpoint, compute which side of the other segment it lies
// if both endpoints lie on the same side of the other segment,
// the segments do not intersect
int Pq1 = CGAlgorithms.OrientationIndex(p1, p2, q1);
int Pq2 = CGAlgorithms.OrientationIndex(p1, p2, q2);
if ((Pq1 > 0 && Pq2 > 0) || (Pq1 < 0 && Pq2 < 0))
{
return(DontIntersect);
}
int Qp1 = CGAlgorithms.OrientationIndex(q1, q2, p1);
int Qp2 = CGAlgorithms.OrientationIndex(q1, q2, p2);
if ((Qp1 > 0 && Qp2 > 0) || (Qp1 < 0 && Qp2 < 0))
{
return(DontIntersect);
}
bool collinear = (Pq1 == 0 && Pq2 == 0 && Qp1 == 0 && Qp2 == 0);
if (collinear)
{
return(ComputeCollinearIntersection(p1, p2, q1, q2));
}
/*
* Check if the intersection is an endpoint. If it is, copy the endpoint as
* the intersection point. Copying the point rather than computing it
* ensures the point has the exact value, which is important for
* robustness. It is sufficient to simply check for an endpoint which is on
* the other line, since at this point we know that the inputLines must
* intersect.
*/
if (Pq1 == 0 || Pq2 == 0 || Qp1 == 0 || Qp2 == 0)
{
isProper = false;
if (Pq1 == 0)
{
intPt[0] = new Coordinate(q1);
}
if (Pq2 == 0)
{
intPt[0] = new Coordinate(q2);
}
if (Qp1 == 0)
{
intPt[0] = new Coordinate(p1);
}
if (Qp2 == 0)
{
intPt[0] = new Coordinate(p2);
}
}
else
{
isProper = true;
intPt[0] = Intersection(p1, p2, q1, q2);
}
return(DoIntersect);
}
