/// <summary>
/// For the set of minimal rings comprising a maximal ring,
/// assigns the holes to the shell known to contain them.
/// Assigning the holes directly to the shell serves two purposes:
/// <list type="bullet">
/// <item><description>it is faster than using a point-in-polygon check later on.</description></item>
/// <item><description>it ensures correctness, since if the PIP test was used the point
/// chosen might lie on the shell, which might return an incorrect result from the
/// PIP test</description></item>
/// </list>
/// </summary>
private static void AssignHoles(OverlayEdgeRing shell, IEnumerable <OverlayEdgeRing> edgeRings)
{
foreach (var er in edgeRings)
{
if (er.IsHole)
{
er.Shell = shell;
}
}
}
/// <summary>
/// Finds the single shell, if any, out of
/// a list of minimal rings derived from a maximal ring.
/// The other possibility is that they are a set of (connected) holes,
/// in which case no shell will be found.
/// </summary>
/// <returns>The shell ring, if there is one
/// or <c>null</c>, if all rings are holes
/// </returns>
private OverlayEdgeRing FindSingleShell(IEnumerable <OverlayEdgeRing> edgeRings)
{
int shellCount = 0;
OverlayEdgeRing shell = null;
foreach (var er in edgeRings)
{
if (!er.IsHole)
{
shell = er;
shellCount++;
}
}
Assert.IsTrue(shellCount <= 1, "found two shells in EdgeRing list");
return(shell);
}
public List <OverlayEdgeRing> BuildMinimalRings(GeometryFactory geometryFactory)
{
LinkMinimalRings();
var minEdgeRings = new List <OverlayEdgeRing>();
var e = _startEdge;
do
{
if (e.EdgeRing == null)
{
var minEr = new OverlayEdgeRing(e, geometryFactory);
minEdgeRings.Add(minEr);
}
e = e.NextResultMax;
} while (e != _startEdge);
return(minEdgeRings);
}
