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Skinning

Skinning is the fine art of defining a surface using two or more profiles. In Blender you do so by preparing as many curves of the the desired shape and then converting them to a single NURBS surface.

A Surface curve for skinning.

As an example we will create a sailboat. The first thing to do, in side view (3 NumPad), is to add a Surface Curve. Be sure to add a Surface curve and not a curve of Bézier or NURBS flavour, or the trick won’t work (A Surface curve for skinning).

Profile of the ship.

Give the curve the shape of the middle cross section of the boat, by adding vertices as needed with the Split button and, possibly, by setting the NURBS to Endpoint both on “U” and “V” (Profile of the ship) as needed.

Now duplicate (⇧ ShiftD) the curve as many times as necessary, to the left and to the right (Multiple profiles along ship’s axis). Adjust the curves to match the various sections of the ship at different points along its length. To this end, blueprints help a lot. You can load a blueprint on the background (as we did for the logo design in this chapter) to prepare all the cross section profiles (Multiple profiles of the correct shapes).

Multiple profiles along ship’s axis.

Note that the surface we’ll produce will be smoothed from one profile to the next. To create abrupt changes you would need to place profiles quite close to each other, as is the case for the profile selected in (Multiple profiles of the correct shapes).If you are converting the hull to a mesh afterwards, a mirror modifier is a handy tool to speed things up. but a mirror modifier can't be applied for curves. if that is a problem you shouldn't use them.

Multiple profiles of the correct shapes.

Now select all curves (with A or B), and join them by pressing CtrlJ and by answering “Yes” to the question “Join selected NURBS?”. The profiles are all highlighted in (Joined profiles).

Joined profiles.

Now switch to Edit mode (⇆ Tab) and select all control points with A; then press F. The profiles should be “skinned” and converted to a surface (Skinned surface in Edit mode).

Note
As should be evident from the first and last profiles in this example, the cross-sections need not be defined on a family of mutually parallel planes.


WARNING
In some cases (i.e. when joining only two curves) the resulting surface may NOT be displayed after you press F. So you need to click on Endpoint U/V or Uniform U/V buttons on Curve Tools panel to correct this issue.


Skinned surface in Edit mode.

Tweak the surface, if necessary, by moving the control points. (Final hull) shows a shaded view. You will very probably need to increase ResolU and ResolV to obtain a better shape.

Final hull.
Profile setup
The only limitation to this otherwise very powerful technique is that all profiles must exhibit the same number of control points. This is why it is a good idea to model the most complex cross section first and then duplicate it, moving control points as needed, without adding or removing them, as we’ve shown in this example.