Offset Surfaces

Once patches have been generated and fitted, this constitutes a surface called OUTER. This is the surface which is generated from the stored orthogonal and 3D curves.

Figure 3:170. Surface Patches Dialog - Output page.

The OUTER surface can be offset by a constant distance to, typically, create an inner hull. The offset is performed in a direction normal to the original surface.

Offset the OUTER surface

1. Open the Surface Patches dialog and switch to the Offset page.

   Make sure the currently selected surface is OUTER, as this is the only surface which can be offset.

2. Type a name for the new surface, a distance to offset from the OUTER surface and click Offset.

   Important: Surfaces containing flat (planar) patches generated by the Patch and Curve Editor cannot currently be offset.

An initial check is made to ensure that the curvature of each patch of the outer surface is sufficiently large enough to allow an offset at the given distance. If the curvature at any patch is too small, a warning is given and the user can discontinue the operation. Offsetting a patch with a small curvature will produce unpredictable results.

Up to 10 offset surfaces can be created. Only one surface can be active (current) at any time.

Change the currently selected surface

• Choose the required surface from the list and click Select.

  Until another surface is selected, all operations (display, check, output ) on fitted patches are performed on the current surface.

The integrity of the current surface can be checked by selecting the Surface option on the Check page of the Surface Patches dialog. This will measure the normal distance of each patch from the currently selected surface against the OUTER surface in order to check for anomalies.