/// <summary>
/// Find the innermost enclosing shell EdgeRing containing the argument EdgeRing, if any.
/// The innermost enclosing ring is the <i>smallest</i> enclosing ring.
/// The algorithm used depends on the fact that:
/// ring A contains ring B iff envelope(ring A) contains envelope(ring B).
/// This routine is only safe to use if the chosen point of the hole
/// is known to be properly contained in a shell
/// (which is guaranteed to be the case if the hole does not touch its shell).
/// </summary>
/// <param name="shellList"></param>
/// <param name="testEr"></param>
/// <returns>Containing EdgeRing, if there is one <br/>
/// or <c>null</c> if no containing EdgeRing is found.</returns>
public static EdgeRing FindEdgeRingContaining(EdgeRing testEr, IList <EdgeRing> shellList)
{
var testRing = testEr.Ring;
var testEnv = testRing.EnvelopeInternal;
//var testPt = testRing.GetCoordinateN(0);
EdgeRing minShell = null;
Envelope minShellEnv = null;
foreach (var tryShell in shellList)
{
var tryShellRing = tryShell.Ring;
var tryShellEnv = tryShellRing.EnvelopeInternal;
if (minShell != null)
{
minShellEnv = minShell.Ring.EnvelopeInternal;
}
// the hole envelope cannot equal the shell envelope
// (also guards against testing rings against themselves)
if (tryShellEnv.Equals(testEnv))
{
continue;
}
// hole must be contained in shell
if (!tryShellEnv.Contains(testEnv))
{
continue;
}
var testPt = CoordinateArrays.PointNotInList(testRing.Coordinates, tryShellRing.Coordinates);
bool isContained = PointLocation.IsInRing(testPt, tryShellRing.Coordinates);
// check if this new containing ring is smaller than the current minimum ring
if (isContained)
{
if (minShell == null || minShellEnv.Contains(tryShellEnv))
{
minShell = tryShell;
minShellEnv = minShell.Ring.EnvelopeInternal;
}
}
}
return(minShell);
}