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Basic Application of the Surface Continuity Manager
By Jeremy Birn

The Deformation > SurfaceContinuityManager+ plug-in is designed to be activated after you have already fitted together multiple NURBS surfaces, using your choice of other modeling tools or techniques. The specific job of the SurfaceContinuityManager+ plug-in is to maintain continuity between the surfaces. Although the plug-in itself is simple to use, its approach to NURBS continuity requires that multi-surface NURBS structures be built in a particular way — it only holds together surfaces that already have a row of vertices sharing the same positions along one edge when the plug-in is first activated.

The Draw > Zip Surfaces function is often used to bring surfaces together before activating SurfaceContinuityManager+. After Zip Surfaces makes the surfaces touch at the edges, SurfaceContinuityManager+ creates a continuity of curvature to hide the seam, and maintains a persistent relationship between the surfaces to hold them together during animation. This quick tutorial shows the basics of how to Zip Surfaces and then apply SurfaceContinuityManager+:

1. In the Model module, select Get>Primitive>Grid, and select "Cubic" NURBS in both X and Z. Leave the X and Z Cell Size at 1, and the X and Z Cell Count at 10, and click OK.

2. With the grid selected, select Effect>Randomize, increase the Y value to 0.5 (up from the default 0.05), and click OK.

3. Use the d supra-key to duplicate the model, and then translate the duplicate to the right of the original.

4. Multi-select both models, and Draw > Zip Surfaces. Click on the point on the lower right corner of the left model, select the V direction in the Zipper Direction dialog box, and click OK.

5. Click on the CV on the lower left corner of the other model, and choose the V direction. The Zip Surfaces dialog will open. Slide the Number of Points Up slider all the way to the right, until both surfaces are joined together. Click OK. The two surfaces will now be touching each other, with no visible gap or space between them. However, there will still be a sharp change of angle and curvature along the seam between them.

6. With the two surfaces still Multi-selected, choose Deformation > SurfaceContinuityManager+. Click OK at the dialog box. The SurfaceContinuityManager+ plug-in will add its icon to the scene, which resembles an adhesive bandage. The seam between the two surfaces is no longer visible.

7. With the two surfaces still Multi-selected, go into TAG mode, and try moving different points on the two models. Because the SurfaceContinuityManager+ is a persistent plug-in effect, it works continuously as you reshape them to make your models appear seamless.

NOTE: If a discontinuity develops as you drag points, just press the r key to refresh the scene.

Contrast these results with having used Draw>Merge Surfaces to combine the two surfaces. Merge Surfaces would have created a new surface that was a single object, looking similar in appearance to the pair of objects that are now seamlessly stitched together with the Surface Continuity Manager. However, the SurfaceContinuityManager+ plug-in can also be used to seamlessly unite more complex groups of surfaces, producing multi-surface NURBS models which never could have been represented with a single NURBS object.

With the Surface Continuity Manager, entire character and creature models can be created as a seamless "quilt" of multiple NURBS surfaces. This basic approach has already been used in many productions, using customized software written in-house at a number of larger studios. This is actually the most popular approach to assembling NURBS surfaces for feature films - very few of the NURBS creatures that you have seen in feature films contained blends, for example. The next tutorials cover the creation of more complex groups of surfaces, as can be used to put together creatures and characters with the Surface Continuity Manager.

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This tutorial copyright © 1999-2000 by Jeremy Birn.
Please do not duplicate any part fo this tutorial without written permission.