Menu : SURFACE

Command: Design:Skin

Shortcut : None

This command creates a skin surface directly over a set of 3D section curves. The defining curves must located in a cross-section curve-set. They must all have the same number of control points and be in the correct order.

A parameter box appears requesting the interpolation method. The choices are Bézier and B-spline. B-spline interpolation generally gives smoother results than Bézier. However, if the section curves are very unevenly spaced, then Bézier interpolation may produce better results.

There are several ways to produce the defining curves. One way is to input them as 2D curves first, then change them to 3D curves with CURVEÞChange:Dimension. Finally, use 3D editing and transformations for modifying and locating them in 3D.

You may of course input 3D curves directly or read them in from a data transfer file. Remember that all curves need to have the same number of control points.

A special method of controlling the lengthwise shape of a skin surface is achieved as follows. Select the 3D sections, and issue the command CURVEÞChange:Interpolate. This produces the surface boundary curves in a 3D-projection set. You may edit these by changing their control points (not knots, as they are tied to the section locations!). When you give command Skin again, the resulting surface will follow the edited lengthwise shape. This works with open section curves only.

This is a suprisingly versatile way of creating surfaces. For example consider the modeling of a plate with an ornate rim shown below. The three curves on the left below were created by drawing one of the end curves in a 2D cross section curve set. This curve was then copied twice and the first copy was edited in the area of the rim. The cross section curve set was then changed to 3D curves using CURVEÞChange:Dimension choosing the X projection direction. The second curve in the set was then rotated around Z by 15 degrees and the third curve was also rotated by 30 degrees. This gives three curves around a 30-degree arc where the first and last curves are identical. These curves were then skinned to produce the surface shown.

This portion of the plate rim was then copied and rotated by 30 degrees around Z 11 times to form the complete rim.