Crowning Complex Shapes

Often designers will want to “crown” a complex surface, such as this star shape. This one can be built, but we’ll have to accept that the corners of the star will fade to flat at the ends.

There are several other conceivable solutions to this little problem, but which you use really depends on what you want the surface to look like in the end. I find that when users struggle to build their idea in CAD, it’s usually because the user hasn’t really figured out exactly what he’s trying to make.

I usually recommend getting out a ball of clay and working through it physically at first, just to prove to yourself that the shape is “real”, i.e. it’s a shape that can exist in 3D space. You’d be amazed how often people fool themselves into believing that non-existent shapes can be built in CAD! Once you’ve proven that the shape can exist in clay, then pick up a pencil and start working out your patch layout, keeping in mind that all NURBS surfaces are 4-sided. If you can draw the shape using only 4-sided surfaces, you’re golden. If not, you’re just not looking hard enough!

Keep up the good work, and keep those problems coming!