/**
* 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.
* <p>
* 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.
*
* @param pts
* @return
*/
private ICoordinateList Reduce(ICoordinateList inputPts)
{
ICoordinateList polyPts = ComputeOctRing(inputPts);
// unable to compute interior polygon for some reason
if (polyPts == null)
{
return(inputPts);
}
// add points defining polygon
ICoordinateList reducedSet = new CoordinateCollection();
int nCount = polyPts.Count;
for (int i = 0; i < nCount; i++)
{
if (!reducedSet.Contains(polyPts[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.
nCount = inputPts.Count;
for (int i = 0; i < nCount; i++)
{
if (!CGAlgorithms.IsPointInRing(inputPts[i], polyPts))
{
reducedSet.Add(inputPts[i]);
}
}
return(reducedSet);
}
public bool IsInside(Coordinate pt)
{
return(CGAlgorithms.IsPointInRing(pt, pts));
}