/// <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.
/// Notice 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 static Coordinate[] Reduce(Coordinate[] pts)
{
Coordinate[] polyPts = ComputeOctRing(pts);
// unable to compute interior polygon for some reason
if (polyPts == null)
{
return(pts);
}
// add points defining polygon
Iesi.Collections.Generic.SortedSet <Coordinate> reducedSet = new Iesi.Collections.Generic.SortedSet <Coordinate>();
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 < pts.Length; i++)
{
if (!CgAlgorithms.IsPointInRing(pts[i], polyPts))
{
reducedSet.Add(pts[i]);
}
}
Coordinate[] arr = new Coordinate[reducedSet.Count];
reducedSet.CopyTo(arr, 0);
return(arr);
}
/// <summary>
///
/// </summary>
/// <param name="p"></param>
/// <param name="ring"></param>
/// <returns></returns>
private static LocationType LocateInPolygonRing(Coordinate p, IBasicGeometry ring)
{
// can this test be folded into IsPointInRing?
if (CgAlgorithms.IsOnLine(p, ring.Coordinates))
{
return(LocationType.Boundary);
}
if (CgAlgorithms.IsPointInRing(p, ring.Coordinates))
{
return(LocationType.Interior);
}
return(LocationType.Exterior);
}
/// <summary>
///
/// </summary>
/// <param name="p"></param>
/// <param name="poly"></param>
/// <returns></returns>
public static bool ContainsPointInPolygon(Coordinate p, IPolygon poly)
{
if (poly.IsEmpty)
{
return(false);
}
LinearRing shell = (LinearRing)poly.Shell;
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.NumHoles; i++)
{
LinearRing hole = (LinearRing)poly.GetInteriorRingN(i);
if (CgAlgorithms.IsPointInRing(p, hole.Coordinates))
{
return(false);
}
}
return(true);
}
/// <summary>
///
/// </summary>
/// <param name="pt"></param>
/// <returns></returns>
public virtual bool IsInside(Coordinate pt)
{
return(CgAlgorithms.IsPointInRing(pt, _pts));
}