Working with Geometry Cache in Maya 8

November 13, 2006 11:17 pm

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In my Maya 8 review, I mentioned that one of the new features in this release is the capability to create Geometry Caches for your animated models. If you are working within Maya this is useful if you want the animation to playback faster. What the Geometry Cache does is bake all the deformers and animation onto a cache. The animation is then read from the hard disk istead of being calculated for each frame.

There are different things you can do with the cached animation. For example, if at some point the deformations were not as you expected, you can "replace" those keys, fixing those deformations. You can also re-time the animation, or even import other cache files into your project. I won't go into details on these because you can know more about them in the Maya help. Instead, I will share an idea for those that work with different 3d apps, or even different versions of Maya.



Using the Geometry Cache in conjuction with the FBX exporter lets you share information between different 3d animation software packages. The FBX is a standard file format that can be imported into almost any existing big commercial 3D software (for example MotionBuilder, Softimage, or MAX). This format not only lets you export models, but also rigs, lights, and even skinning information. This means you can skin your character in Maya, animate them in MotionBuilder, and then bring them into MAX for rendering. People have actually been doing that for a long time, but what happens if you are using some kind of deformers that are specific for a certain application? Maybe you used muscle simulations or syflex cloth for your animated character in Maya, but those animations might not translate well into MAX, and the final result might not be as good as you had expected.



For this excercise, I animated one of my characters in Maya 8, then created a Geometry Cache for her which I exported to FBX, and then imported back into an empty scene. The model doesn't have any high-end deformers, but it still serves to demonstrate the technique. After the character was animated, I created a Geometry Cache to bake the animation onto cache files. After doing this you can even delete your rig since you won't be using it anymore. Note: Make sure you delete your rig only if you are certain you won't need to change anything in the animation.

With the model animated only with the Cache, you then create a "quick selection set" that includes the objects that have a Geometry Cache (the head and body in this case), and then you export everything as FBX. You have to make sure you have the latest version of the plug-in (by the time I wrote this article the latest version was 2006.08). Previous versions of the plug-in will not work. Below are shown the exporting options you have to set when you are exporting.



You can find explanations of these options in the FBX documentation. I want to draw your attention to "Bake complex animation," "Export Quick Select Set as Geometry Cache File(s)," and "Export to Version." The first option is used to bake the animation of deformers, for example, muscle systems. The second option is where you select the quick select set you created above, and the last option is the plug-in version (again, make sure you export to the latest version). When you click Export, Maya will take a little while and then your model and animation will be exported.

This creates an FBX file and a folder containing caches for your animated objects. If you plan to move this FBX file into another computer, make sure that you copy all those cache files as well, or else it won't work.

If I had MAX, I would have tried importing this animation into MAX, however that is not the case so I imported that back into an empty Maya scene. When you import an FBX file that includes animation you are allowed to select which "animation take" you want to import (as seen on the image below).



After the import you will see your animated model on your viewport. If you deleted the rig before exporting, you will see that the character is animated using the cache that was exported with the FBX, however don't delete the rig unless you are extremely sure you won't be needing it anymore.

With the Geometry Cache you can export the per-vertex animation of any model or character you have. This is useful not only when you work with older versions of Maya but also when you work with different apps and you need to exchange information between them. I hope you found this article useful. I'd like to thank the Autodesk Helpdesk for helping me while I was trying to learn how to work with this feature.

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Animation Alley is a regular featured column with Renderosity Staff Columnist Sergio Rosa [nemirc]. Sergio discusses on computer graphics software, animation techniques, and technology. He also hosts interviews with professionals in the animation and cinematography fields.
November 20, 2006

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Article Comments

nickcharles ( posted at 12:00AM Sun, 26 November 2006

Excellent article, Sergio. Geometry Cache is a fantastic feature.

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