/// <summary>
        /// Circles the check data node.
        /// </summary>
        /// <returns>
        /// The check data node.
        /// </returns>
        /// <param name='n'>
        /// N.
        /// </param>
        /// <param name='ys'>
        /// Ys.
        /// </param>
        public static VCircleEvent CircleCheckDataNode(VDataNode n, double ys)
        {
            VDataNode l = VNode.LeftDataNode(n);
            VDataNode r = VNode.RightDataNode(n);

            if (l == null || r == null || l.DataPoint == r.DataPoint || l.DataPoint == n.DataPoint || n.DataPoint == r.DataPoint)
            {
                return(null);
            }

            if (MathTools.ccw(l.DataPoint.X, l.DataPoint.Y, n.DataPoint.X, n.DataPoint.Y, r.DataPoint.X, r.DataPoint.Y, false) <= 0)
            {
                return(null);
            }

            Vector2D     Center = Fortune.CircumCircleCenter(l.DataPoint, n.DataPoint, r.DataPoint);
            VCircleEvent VC     = new VCircleEvent();

            VC.NodeN  = n;
            VC.NodeL  = l;
            VC.NodeR  = r;
            VC.Center = Center;
            VC.Valid  = true;
            if (VC.Y >= ys)
            {
                return(VC);
            }

            return(null);
        }
        /// <summary>
        /// Computes the voronoi graph.
        /// </summary>
        /// <returns>
        /// The voronoi graph.
        /// </returns>
        /// <param name='Datapoints'>
        /// Datapoints.
        /// </param>
        /// <exception cref='Exception'>
        /// Represents errors that occur during application execution.
        /// </exception>
        public static VoronoiGraph ComputeVoronoiGraph(IEnumerable Datapoints)
        {
            PriorityQueue <VEvent> PQ   = new PriorityQueue <VEvent>(PriorityQueueType.Minimum);
            Hashtable    CurrentCircles = new Hashtable();
            VoronoiGraph VG             = new VoronoiGraph();
            VNode        RootNode       = null;

            foreach (Vector2D V in Datapoints)
            {
                PQ.Enqueue(new VDataEvent(V));
            }

            while (PQ.Count > 0)
            {
                VEvent      VE = PQ.Dequeue() as VEvent;
                VDataNode[] CircleCheckList;

                if (VE is VDataEvent)
                {
                    RootNode = VNode.ProcessDataEvent(VE as VDataEvent, RootNode, VG, VE.Y, out CircleCheckList);
                }
                else if (VE is VCircleEvent)
                {
                    CurrentCircles.Remove(((VCircleEvent)VE).NodeN);
                    if (!((VCircleEvent)VE).Valid)
                    {
                        continue;
                    }
                    RootNode = VNode.ProcessCircleEvent(VE as VCircleEvent, RootNode, VG, VE.Y, out CircleCheckList);
                }
                else
                {
                    throw new Exception("Got event of type " + VE.GetType().ToString() + "!");
                }

                foreach (VDataNode VD in CircleCheckList)
                {
                    if (CurrentCircles.ContainsKey(VD))
                    {
                        ((VCircleEvent)CurrentCircles[VD]).Valid = false;
                        CurrentCircles.Remove(VD);
                    }

                    VCircleEvent VCE = VNode.CircleCheckDataNode(VD, VE.Y);
                    if (VCE != null)
                    {
                        PQ.Enqueue(VCE);
                        CurrentCircles[VD] = VCE;
                    }
                }

                if (VE is VDataEvent)
                {
                    Vector2D DP = ((VDataEvent)VE).DataPoint;
                    foreach (VCircleEvent VCE in CurrentCircles.Values)
                    {
                        if (MathTools.Dist(DP.X, DP.Y, VCE.Center.X, VCE.Center.Y) < VCE.Y - VCE.Center.Y && Math.Abs(MathTools.Dist(DP.X, DP.Y, VCE.Center.X, VCE.Center.Y) - (VCE.Y - VCE.Center.Y)) > 1e-10)
                        {
                            VCE.Valid = false;
                        }
                    }
                }
            }

            return(VG);
        }
        /// <summary>
        /// Circles the check data node.
        /// </summary>
        /// <returns>
        /// The check data node.
        /// </returns>
        /// <param name='n'>
        /// N.
        /// </param>
        /// <param name='ys'>
        /// Ys.
        /// </param>
        public static VCircleEvent CircleCheckDataNode( VDataNode n, double ys )
        {
            VDataNode l = VNode.LeftDataNode( n );
            VDataNode r = VNode.RightDataNode( n );
            if( l == null || r == null || l.DataPoint == r.DataPoint || l.DataPoint == n.DataPoint || n.DataPoint == r.DataPoint ) {
                return null;
            }

            if( MathTools.ccw( l.DataPoint.X, l.DataPoint.Y, n.DataPoint.X, n.DataPoint.Y, r.DataPoint.X, r.DataPoint.Y, false ) <= 0 ) {
                return null;
            }

            Vector2D Center = Fortune.CircumCircleCenter( l.DataPoint, n.DataPoint, r.DataPoint );
            VCircleEvent VC = new VCircleEvent();
            VC.NodeN = n;
            VC.NodeL = l;
            VC.NodeR = r;
            VC.Center = Center;
            VC.Valid = true;
            if( VC.Y >= ys ) {
                return VC;
            }

            return null;
        }
        /// <summary>
        /// Processes the circle event.
        /// </summary>
        /// <returns>
        /// The circle event.
        /// </returns>
        /// <param name='e'>
        /// E.
        /// </param>
        /// <param name='Root'>
        /// Root.
        /// </param>
        /// <param name='VG'>
        /// V.
        /// </param>
        /// <param name='ys'>
        /// Ys.
        /// </param>
        /// <param name='CircleCheckList'>
        /// Circle check list.
        /// </param>
        public static VNode ProcessCircleEvent(VCircleEvent e, VNode Root, VoronoiGraph VG, double ys, out VDataNode[] CircleCheckList)
        {
            VDataNode a;
            VDataNode b;
            VDataNode c;
            VEdgeNode eu;
            VEdgeNode eo;

            b = e.NodeN;
            a = VNode.LeftDataNode(b);
            c = VNode.RightDataNode(b);
            if (a == null || b.Parent == null || c == null || !a.DataPoint.Equals(e.NodeL.DataPoint) || !c.DataPoint.Equals(e.NodeR.DataPoint))
            {
                CircleCheckList = new VDataNode[] {};

                return(Root); // Abbruch da sich der Graph ver 0/00ndert hat
            }

            eu = b.Parent as VEdgeNode;
            CircleCheckList = new VDataNode[] { a, c };

            //1. Create the new Vertex
            Vector2D VNew = new Vector2D(e.Center.X, e.Center.Y);

            VG.Vertizes.Add(VNew);

            //2. Find out if a or c are in a distand part of the tree (the other is then b's sibling) and assign the new vertex
            if (eu.Left == b)    // c is sibling
            {
                eo = VNode.EdgeToRightDataNode(a);

                // replace eu by eu's Right
                eu.Parent.Replace(eu, eu.Right);
            }
            else     // a is sibling
            {
                eo = VNode.EdgeToRightDataNode(b);

                // replace eu by eu's Left
                eu.Parent.Replace(eu, eu.Left);
            }

            eu.Edge.AddVertex(VNew);
            eo.Edge.AddVertex(VNew);

            //2. Replace eo by new Edge
            VoronoiEdge VE = new VoronoiEdge();

            VE.LeftData  = a.DataPoint;
            VE.RightData = c.DataPoint;
            VE.AddVertex(VNew);
            VG.Edges.Add(VE);

            VEdgeNode VEN = new VEdgeNode(VE, false);

            VEN.Left  = eo.Left;
            VEN.Right = eo.Right;
            if (eo.Parent == null)
            {
                return(VEN);
            }

            eo.Parent.Replace(eo, VEN);

            return(Root);
        }
        /// <summary>
        /// Processes the circle event.
        /// </summary>
        /// <returns>
        /// The circle event.
        /// </returns>
        /// <param name='e'>
        /// E.
        /// </param>
        /// <param name='Root'>
        /// Root.
        /// </param>
        /// <param name='VG'>
        /// V.
        /// </param>
        /// <param name='ys'>
        /// Ys.
        /// </param>
        /// <param name='CircleCheckList'>
        /// Circle check list.
        /// </param>
        public static VNode ProcessCircleEvent( VCircleEvent e, VNode Root, VoronoiGraph VG, double ys, out VDataNode[] CircleCheckList )
        {
            VDataNode a;
            VDataNode b;
            VDataNode c;
            VEdgeNode eu;
            VEdgeNode eo;

            b = e.NodeN;
            a = VNode.LeftDataNode( b );
            c = VNode.RightDataNode( b );
            if( a == null || b.Parent == null || c == null || !a.DataPoint.Equals( e.NodeL.DataPoint ) || !c.DataPoint.Equals( e.NodeR.DataPoint ) ) {
                CircleCheckList = new VDataNode[]{};

                return Root; // Abbruch da sich der Graph ver 0/00ndert hat
            }

            eu = b.Parent as VEdgeNode;
            CircleCheckList = new VDataNode[] {a,c};

            //1. Create the new Vertex
            Vector2D VNew = new Vector2D( e.Center.X, e.Center.Y );

            VG.Vertizes.Add( VNew );

            //2. Find out if a or c are in a distand part of the tree (the other is then b's sibling) and assign the new vertex
            if( eu.Left == b ) { // c is sibling
                eo = VNode.EdgeToRightDataNode( a );

                // replace eu by eu's Right
                eu.Parent.Replace( eu, eu.Right );
            } else { // a is sibling
                eo = VNode.EdgeToRightDataNode( b );

                // replace eu by eu's Left
                eu.Parent.Replace( eu, eu.Left );
            }

            eu.Edge.AddVertex( VNew );
            eo.Edge.AddVertex( VNew );

            //2. Replace eo by new Edge
            VoronoiEdge VE = new VoronoiEdge();
            VE.LeftData = a.DataPoint;
            VE.RightData = c.DataPoint;
            VE.AddVertex( VNew );
            VG.Edges.Add( VE );

            VEdgeNode VEN = new VEdgeNode( VE, false );
            VEN.Left = eo.Left;
            VEN.Right = eo.Right;
            if( eo.Parent == null ) {
                return VEN;
            }

            eo.Parent.Replace( eo, VEN );

            return Root;
        }