/// <summary> Finds and removes all cut edges from the graph.</summary> /// <returns> a list of the <see cref="LineString"/>s forming the removed cut edges /// </returns> public ArrayList DeleteCutEdges() { ComputeNextCWEdges(); // label the current set of edgerings FindLabeledEdgeRings(dirEdges); /// <summary> Cut Edges are edges where both dirEdges have the same label. /// Delete them, and record them /// </summary> ArrayList cutLines = new ArrayList(); for (IEnumerator i = dirEdges.GetEnumerator(); i.MoveNext();) { PolygonizeDirectedEdge de = (PolygonizeDirectedEdge)i.Current; if (de.Marked) { 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 {@link LineStrings} that formed dangles /// </returns> public ICollection DeleteDangles() { ArrayList 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); ArrayList 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(dangleLines); }
/// <summary> /// Add a <see cref="LineString"/> forming an edge of the polygon graph. /// </summary> /// <param name="line">the line to Add /// </param> public void AddEdge(LineString line) { if (line.IsEmpty) { return; } ICoordinateList linePts = CoordinateCollection.RemoveRepeatedCoordinates(line.Coordinates); Coordinate startPt = linePts[0]; Coordinate endPt = linePts[linePts.Count - 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.Count - 2], false); Edge edge = new PolygonizeEdge(line); edge.SetDirectedEdges(de0, de1); Add(edge); }