;
PolyCAD
When a X-Topology surface is generated the last face (patch) to be identifed will generally mark the boundary. For this to happen the references topology curves must form an easily identifyable surface. However, sometime the definition may be closed and the form produced by the X-Topolology surface will be more solid with every face filled in. It is possible to inform the surface generation process that it should not patch a face by marking the boundary curves with the 'Force Curve to Surface Boundary' The surface modeller will not create a patch on a face where all the curve edges have been marked with this attribute. This option is available from X-Topology Curve menu, (Right-Click -> X-Topology Curve -> Force Curve to be Surface Boundary), and the multiple selection menu (Right-Click -> Multiple Selection -> Force Curve to be Surface Boundary).