/// <summary>
/// Finds and removes all cut edges from the graph.
/// </summary>
/// <returns>A list of the <c>LineString</c>s forming the removed cut edges.</returns>
public virtual IList DeleteCutEdges()
{
ComputeNextCWEdges();
// label the current set of edgerings
FindLabeledEdgeRings(dirEdges);
/*
* Cut Edges are edges where both dirEdges have the same label.
* Delete them, and record them
*/
IList cutLines = new ArrayList();
for (IEnumerator i = dirEdges.GetEnumerator(); i.MoveNext();)
{
PolygonizeDirectedEdge de = (PolygonizeDirectedEdge)i.Current;
if (de.IsMarked)
{
continue;
}
PolygonizeDirectedEdge sym = (PolygonizeDirectedEdge)de.Sym;
if (de.Label == sym.Label)
{
de.Marked = true;
sym.Marked = true;
// save the line as a cut edge
PolygonizeEdge e = (PolygonizeEdge)de.Edge;
cutLines.Add(e.Line);
}
}
return(cutLines);
}
/// <summary>
/// Marks all edges from the graph which are "dangles".
/// Dangles are which are incident on a node with degree 1.
/// This process is recursive, since removing a dangling edge
/// may result in another edge becoming a dangle.
/// In order to handle large recursion depths efficiently,
/// an explicit recursion stack is used.
/// </summary>
/// <returns>A List containing the LineStrings that formed dangles.</returns>
public virtual IList DeleteDangles()
{
IList nodesToRemove = FindNodesOfDegree(1);
ISet dangleLines = new HashedSet();
Stack nodeStack = new Stack();
for (IEnumerator i = nodesToRemove.GetEnumerator(); i.MoveNext();)
{
nodeStack.Push(i.Current);
}
while (nodeStack.Count != 0)
{
Node node = (Node)nodeStack.Pop();
DeleteAllEdges(node);
IList nodeOutEdges = node.OutEdges.Edges;
for (IEnumerator i = nodeOutEdges.GetEnumerator(); i.MoveNext();)
{
PolygonizeDirectedEdge de = (PolygonizeDirectedEdge)i.Current;
// delete this edge and its sym
de.Marked = true;
PolygonizeDirectedEdge sym = (PolygonizeDirectedEdge)de.Sym;
if (sym != null)
{
sym.Marked = true;
}
// save the line as a dangle
PolygonizeEdge e = (PolygonizeEdge)de.Edge;
dangleLines.Add(e.Line);
Node toNode = de.ToNode;
// add the toNode to the list to be processed, if it is now a dangle
if (GetDegreeNonDeleted(toNode) == 1)
{
nodeStack.Push(toNode);
}
}
}
return(new ArrayList(dangleLines));
}
/// <summary>
/// Add a <c>LineString</c> forming an edge of the polygon graph.
/// </summary>
/// <param name="line">The line to add.</param>
public virtual void AddEdge(LineString line)
{
if (line.IsEmpty)
{
return;
}
ICoordinate[] linePts = CoordinateArrays.RemoveRepeatedPoints(line.Coordinates);
ICoordinate startPt = linePts[0];
ICoordinate endPt = linePts[linePts.Length - 1];
Node nStart = GetNode(startPt);
Node nEnd = GetNode(endPt);
DirectedEdge de0 = new PolygonizeDirectedEdge(nStart, nEnd, linePts[1], true);
DirectedEdge de1 = new PolygonizeDirectedEdge(nEnd, nStart, linePts[linePts.Length - 2], false);
Edge edge = new PolygonizeEdge(line);
edge.SetDirectedEdges(de0, de1);
Add(edge);
}