Managing Closed Curves with the Lofted Surface Command

Specific options for managing closed curves are available under the More Options node of the Lofted Surface command, when the Type is set to Grid. Some mini-dialog boxes will be available once these options are applicable (displayed when the More Options node is expanded). They remain active but not visible when the More Options node is collapsed.
First of all, it is necessary to take into account what follows:

• A set of boundaries can be composed either of closed or of open curves. When using sets of mixed closed and open curves, the command behaves as if all were open curves.
• The possibility to close the resulting surface is proposed in the applicable directions (no proposal if there is no possibility).
• The origins of the closure, where a Close mini-dialog box is displayed, are on the first selected curve of the opposite set (if any).
  
  
  
  
  • When the box is checked, the resulting surface will be closed.
  • When the box is cleared, the resulting surface will not be closed.
     
• You can redefine the origin of the closed curves, so as to avoid twisting and to define a large number of different resulting surfaces based on the same sets of curves.
  
  

  About redefining the origins If there is no V parameter curve, origins are not automatically redefined. A curve is built so as to interpolate them for the closure. See the example below: the surface on the right is wavy since there is a lack of correspondence on cusp points and no interpolation is done in the middle. If you have a V parameter curve, all origins will be redefined. Please observe that the generated surfaces are geometrically similar regardless of their start points.

  
   
• By default, the first boundary (according to the parameterization) will be selected as the origin, but you can simply change it by selecting a different one in the model (both for Boundary Set A and for Boundary Set B, a Start Boundary selector is available in the selection list). The selected boundary is displayed with a dashed line so as to highlight it better.
  
  
   
• You can manage position, tangency and curvature continuity along the surface closures.
  
  
  
  When the Close check box is selected, the Continuity mini-dialog box is displayed nearby. Its drop-down list enables you to select one of the following constraints:
  

  Position	To apply a positional continuity (G0) constraint along the closure.
  Tangent	To apply a tangency continuity (G1) constraint along the closure.
  Curvature	To apply a curvature continuity (G2) constraint along the closure.

  Specific warnings will be issued if the geometric conditions do not allow the specified constraint to be applied since an incompatibility situation would be generated.