internal PolygonArc(ArcKind kind, int poly1Index, int poly2Index, GridEdge edge)
 {
     this.kind = kind;
     this.poly1Index = poly1Index;
     this.poly2Index = poly2Index;
     this.edge = edge;
 }
 protected PathEdge MakePathEdge(GridEdge edge)
 {
     return new PathEdge(edge.StartLoc, edge.EndLoc);
 }