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Maya 2008 Character Modeling and Animation: Motion Path Animation

In this last excerpt from Maya 2008 Character Modeling and Animation, author Tereza Flaxman explains how to animate an object on a path and edit the animation timing using motion path keys.

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

This month VFXWorld concludes its excerption of the Thomson Course Technology book Maya 2008 Character Modeling and Animation. In this series, VFXWorld readers have taken on the challenge of animating realistic and compelling characters using the latest version of Maya, the powerful 3D graphics and modeling software. Excerpts have shown 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.

Motion path animation is a technique which allows you to animate an object moving along a curve. The curve controls the direction, position and rotation of the object. To create a path animation you first create a curve and then attach an object to it. This excerpt from Maya 2008 Character Modeling and Animation teaches you how to animate a simple object on a path and set motion path keys.

Motion path animation refers to an object or character that is animated on a curve path. This is useful for animating creatures such as fish or snakes. It is also commonly used for rapidly generating blocking animation -- the preliminary positioning of characters in a scene, and subsequent camera adjustments. Path animation can also be used to control camera motion itself, a method that directly mimics the physical camera tracks used in live-action film production.

[Figure 1] CV curve for motion path (left). [Figure 2] The RebuildCurve Options window (right). 

By default, a motion path object moves continuously and evenly along the given path. However, you can adjust this as needed using keyframes to specify location along the path at a particular time.

1. Create a new scene.

2. Press F4 to change Maya to Surfaces mode.

3. Select Create > CV Curve Tool.

4. In the Top view, click several times from right to left to create a loop curve as shown in Figure 1.

5. Select the curve’s last CV. Holding down the V key, move and snap the CV to the curve’s first CV.

6. Select Edit Curve > Open/Close Curve to make a continuous curve. A closed curve is a loop with the first and last edit points coinciding. In this case, you want a closed curve so that your motion path is continuous.

7. Select Edit Curve > Rebuild Curve Option Box.

8. In the options window, make sure that Rebuild Type Uniform is selected, Keep CVs is checked, and Keep Original is unchecked (see Figure 2).

[Figure 3] The Attach to Motion Path Options window (left). [Figure 4] Marker 200 moved close to the horizontal grid axis (right).

9. Click the Rebuild button. This distributes the CVs to uniformly create a smooth curve. Objects animated on smooth curves have smooth motion.

10. Select Create > NURBS Primitives > Sphere.

11. Press F2 to change Maya to Animation mode.

12. With the sphere still selected, Shift-click the curve to select it.

13. Select Animate > Motion Paths > Attach to Motion Path Option Box.

14. In the options window, check Time Range Start/End. Type 1 in the Start Time field, and type 500 in the End Time field. Check the Follow, Front Axis Z, and Up Axis Y options. In the World Up Type drop-down list, choose Scene Up (see Figure 3). Scene Up means that the Up vector of the object on the path tries to align with the scene up axis specified in the preferences. Maya defaults the scene up to positive Y.

15. Click the Attach button.

16. Make sure that the end time of the animation playback range is set to 500.

17. Play the animation. You should see the sphere moving along the curve.

[Figure 5] Position Marker Attributes changed.

Setting Motion Path Markers

Motion path markers allow you to control the speed of your object. The object speed decelerates between close markers, and accelerates between widely spaced markers.

To set a motion path marker, follow these steps:

1. Drag the Time slider to frame 200.

2. Select the motion path curve.

3. In the Channel Box under OUTPUTS, look for MotionPath1.

4. Click MotionPath1. You should see U value.

5. Click the U value to select it.

6. Right-click the U value and select Key Selected. A yellow marker with the number 200 should appear in the curve path.

7. Select the frame 200 marker, and in the Top view, move it close to the horizontal grid axis as shown in Figure 4.

8. Drag the time line to 300.

9. Repeat steps 3 to 6 to set another key on the U value.

Changing the Marker Time

To change the marker time, follow these steps:

1. Drag the time line to frame 400.

2. Set a key for the U value.

3. Select the marker 400 and open its Attribute Editor.

4. Under Position Marker Attributes, type 350 in the Time field as shown in Figure 5. The marker number should change to 350.

5. Play the animation. Notice that the sphere moves according to the time set on the markers.

Conclusion

Motion path animation is useful both for animating objects such as invertebrate animals (as shown here) and even cameras. It can also be used to "block" character animation. In Maya 2008 Character Modeling and Animation: Principles and Practices, a detailed step-by-step tutorial teaches you how to use this technique to animate a fish along a path.

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.

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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