Unwraping complex shapes in Rhino

Discussion in 'Tips, Tutorials & Tools' started by Atomsk, Dec 25, 2004.

  1. Atomsk

    Atomsk Member

    Recently, I posted some progress shots of my first model design, in the Designer's Corner forum. Nobi, the moderator, asked me to explain the technique I used to unwrap the skin of the model. I tought this would be the right forum to provide that information.

    After some experimentation, I found that the key to unwraping any Rhino surface is the "degree" of that surface. If the surface has a degree of greater than 1 in both the "U" and "V" directions, it can't be unwraped, because Rhino assumes that it's a compound curve. Usually you can reduce one of the directions to degree 1, without seriously changing the shape of the surface. It may change slightly, but it will be as close as can be represented in paper.

    Here are the steps I use, YMMV:

    1. If the object is a Polysurface, explode it.

    2. Select each surface and select Analyze->Direction from the menu. Move the pointer over the surface and note the orientation of the two colored arrows. The one that's the same color as your X axis marks the U direction, the one that's the color of Y is V.

    3. Use the Direction tool's Reverse and Swap options to change the U and V directions of each surface, so that all of the components of your old polysurface have the same UV orientation.

    4. Select all the surfaces that you created from the old polysurface.

    5. Change the degree of all the surfaces. There are two ways to do this. First is the Edit->Change Degree command. I prefer the Edit->Rebuild option, because it offers more control, and lets you "clean up" overly complex surfaces. In the Rebuild dialog, set the degree of the U or V dimension to 1, depending on which one already has the lowest degree. You may need to undo the rebuild, and try again with the other dimension, if the results are too "blocky". I usually set the dimension that I'm not flatening to 3, and the point counts to 3 for the degree 1 dim. and 5 for the degree 3.

    6. the result of the rebuild is usually a polysurface, so as soon as the rebuild is complete, and the resultant objects are still selected, do another explode.

    7. Select each new surface individually, and select Surface->Unroll Developable Surface for each. Just hit enter if Rhino asks you to "select curves on surface".

    8. Switch to the top view and you'll see a "stack" of flat parts at the origin. Use Transform->Move, and Transform->Rotate, along with the "End" Osnap, to assemble the separate parts into their original configurations. Then, combine all the smaller parts, with the Merge, Join, or Group commands.

    9. Hide all the 3D parts and arrange the 2D parts into page sized groups. I did the model in 1/1 scale, so I drew a rectangle 34X44 feet, to represent an 8 1/2X11 page, used it to arrange the parts, then shrunk them all to 1/48th their original size. If I want 1/32, I just use a 22.66X29.33 foot square, or 17X24 feet for 1/24.

    10. I had best luck transfering the shapes to Corel Draw in WMF (Windows Metafile) format. Just select the resized components and use File->Export Selected...

    11. Import then onto Corel, and move each group of parts onto its own page.

    12. Remove any excess lines, and the skin is ready for painting.

    Of course, you'll still need to create formers, spars, and joiner strips, for a full up test build, bit that's another lesson.

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