
                      var radius = path.actualBounds.width / 2;
                      var c = path.actualBounds.center;
                      var a0 = c.directionPoint(p0);
                      var av = c.directionPoint(pv);
                      var sweep = av - a0;
                      if (sweep < 0) sweep += 360;
                      var layerThickness = 8;
                      return new go.Geometry()
                        .add(new go.PathFigure(-radius, -radius)) // always make sure the Geometry