Single Projection 3D Building

Building surfaces is also possible using 3D projections and it works in a very similarly manner to the 2D case.

With 3D projections, the command BUILDÞCreate:Surface creates the surface by transforming one or more 2D sections to match the 3D projection curve locations to make a wire framework and then ‘stretching’ a surface over this framework. The projection and section curves may be either B-splines or Bézier, but the resulting surface will always be created in the Bézier format.

The other BUILD menu commands, such as BUILDÞCreate:Cross Sections, BUILDÞSet:Build Parameters and BUILDÞSet:Section Parameters work for 3D projections, too. However secondary projections do not have any meaning in the 3D case.

If there is just one 3D-projection curve defined, the cross-sections are positioned along it by attaching the cross-section origins at the projection curve, with the section curves perpendicular to the projection curve at that point.

How the sections are rotated around the projection curve is determined with a special parameter, the orientation method. It has two alternatives: projective and principal normal. The projective method is generally the preferred method. The principal normal method should be used only in the case of very regularly shaped projection curves. The best example of this is perhaps a spiral curve, where the projective method may produce a slight twist to the surface.