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'Maya 2008 Character Modeling and Animation': NURBS Surface Creation Tools

In this fifth of six excerpts from Maya 2008 Character Modeling and Animation, author Tereza Flaxman explains how to create NURBS surfaces from construction curves, using Maya's Birail and Boundary tools.

All images from Maya 2008 Character Modeling and Animation: Principles and Practices by Tereza Flaxman.

VFXWorld continues excerpting a new series from the Thomson Course Technology book Maya 2008 Character Modeling and Animation. VFXWorld readers will take on the challenge of animating realistic and compelling characters using the latest version of Maya, the powerful 3D graphics and modeling software. Excerpts will show beginning to intermediate animation students and enthusiasts how to create professional quality characters, explaining the full character animation process from pre-production to final full body and facial animation.

Maya offers a diversity of NURBS modeling tools. In this excerpt you will learn how to use two powerful methods for construction surfaces from NURBS curves: the Birail and the Boundary tools.

Understanding the Birail Tool

The Birail tool allows you to create a surface based on three or more curves. This tool sweeps one or more profile curves along two birail curves (path curves).

This tool has three options:

Birail 1 tool. This requires two birail curves and one profile curve (see Figure 1).

Birail 2 tool. This requires two birail curves and two profile curves (see Figure 2).

Birail 3+ tool. This requires three birail curves and two profile curves (see Figure 3).

To create a birail geometry, you need to create three or more curves that must intersect.

[Figure 1] Birail 1 rail and profile curves.

1. Open a new scene.

2. Select Create > CV Curve Tool.

3. In the Front view, create three curves as shown in Figure 4.

4. Look at the curves in the perspective, and make sure that the vertical curve intersects with the two horizontal ones.

[Figure 2] Birail 2 rail and profile curves (above); [Figure 3] Birail 3+ rail and profile curves (below).

5. Select Surfaces > Birail > Birail 1 Tool. The mouse cursor should change to an arrow.

6. Click first on the vertical curve to select it as the profile curve. Second, click the bottom horizontal curve, and third click the top horizontal curve. The horizontal curves are the rail curves (see Figure 5).

7. Press F5 to change to the Smooth Shade All mode, and you should see the Birail geometry.

[Figure 4] Three curves to create a birail surface (left); [Figure 5] Birail tool click sequence.

If you don’t see the birail geometry, it is because the profile curve is not intersecting with the rail curves. An easy way to make sure that the curves are intersecting is to snap the parameterization CV of the vertical curve to the horizontal ones.

Understanding the Boundary Tool

The Boundary tool creates a surface within boundary curves. This tool has two options that decide how the surface is created: Automatically and As Selected.

When you choose the Automatically option, Maya decides how to create the boundary surface. When you choose As Selected, the order in which you pick the curves alters the boundary surface. You also have to choose a common end point option. If you choose Optional, the boundary surface is created even if the curves’ end points don’t match. If you choose Required, the curves common end points must match. The best way to match the curves and end points is using the curve snap feature previously discussed.

1. Open a new scene.

2. In the Front view, create four CV curves as shown in Figure 6. Notice that the two vertical curves were created from top to bottom, and the two horizontal curves were created from left to right.

[Figure 6] Four curves to create a boundary surface; [Figure7] Named curves for the Boundary tool.

  • 3. Name the curves as follows (see Figure 7):
    • Left vertical curve: curve_left
    • Right vertical curve: curve_right
    • Bottom horizontal curve: curve_bottom
    • Top horizontal curve: curve_top

4. Select Surfaces > Boundary Option Box.

5. In the Boundary Options window, click Curve Ordering Automatically, as shown in Figure 8.

6. Select the four curves by clicking on them one by one in any order. The order in which you select the curves does not matter.

7. Click the Apply button. The Boundary Options window should stay on, and a new boundary surface should be created as shown in Figure 9.

8. Delete the new boundary surface. You should see just the four boundary curves.

9. Select Surfaces > Boundary Option Box.

10. In the Boundary Options window, click As Selected.

[Figure 8] The Boundary Options window (above); [Figure 9] Automatic boundary surface generation options (bottom left); [Figure 10] As Selected boundary surface (bottom right).

11. Click first on curve_left, second on curve_bottom, third on curve_right and fourth on curve_top.

12. Click the Apply button.

13. You should see a boundary geometry just like the one created previously with the Automatic option.

14. Delete the boundary surface you just created.

15. Select Surface > Boundary Option Box.

16. Now, click first on curve_left, second on curve_right, third on curve_bottom, and fourth on curve_top. Click the Apply button. You should see a different boundary surface as shown in Figure 10.The geometry was created between different curves; this resulted in a different shape.

Each chapter of Maya 2008 Character Modeling and Animation: Principles and Practices begins by exploring the "why" behind the techniques being presented, followed by step-by-step tutorials to apply your new knowledge. Following a series of hands-on projects, you'll learn how to model, rig and animate, building a comprehensive skill-set as you move progressively through each chapter. Check back to VFXWorld frequently to read new excerpts.

Maya 2008 Character Modeling and Animation: Principles and Practices by Tereza Flaxman. Boston, MA: Thomson Course Technology, 2008. 500 pages with illustrations and CD. ISBN 13: 978-1-58450-556-3; ISBN 10: 1-58450-556-7 ($44.99).

Tereza Flaxman teaches 3D modeling and animation at the Harvard Extension School and Northeastern University. She has been teaching animation for the past seven years at both undergraduate and graduate levels and is a Certified Alias Maya Instructor. Additionally, she has taught at both the School of Film and Animation at the Rochester Institute of Technology (RIT) and at the State University of New York (SUNY). She also works as a freelance animator. Flaxman has more than 15 years of experience with high-end 3D animation software and has used Maya since version 1.0. Her work has been published in several books and magazines and exhibited in shows throughout the U.S. She has an MFA in computer animation from the School of Visual Arts in New York City and a BFA from the University of Oregon.

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