Week 5 Notes
Motion Capture and Character Animation Pipeline
* Useful resources: CMU motion database. check resource menu on course website.
1. Overview
Developing character in 3D contents is quite complex and labor intensive process. Motion capture technology can save some of your time while it provides realitic human motion. But... nothing comes for free! Initial learning curve may be stiff. Here, we will briefly look its design pipeline. We will use two main software packages. One is Motion Builder and the other is Maya. Here, we assume that we've already acquired motion capture data and processed it appropriately using Vicon software. See more details in EVL mocap tutorial page.
Prerequisite
* Character model
It's easier if you following some kind of common naming convention for your skeleton's bone name. If you name your skeleton bones same as Motion Builder's naming convention, it will be much easier to characterize your model in MB.
- check this sample skeleton file: Skeleton_Sample.mb
- sample character file: stickman.mb
2. Export Character to Motion Builder format
We will mostrly use Motion Builder to process and regarget mocap data. So, we need to export our character from maya to motion builder.
- File / Export All : then choose file type as FBX, check the option to use Motion Builder 2011 type
- Exported sample file: stickman.fbx
3. Motion Builder Characterization
Characterization is the process that we build logical control for biped / quadpad type human like control in Motion Builder software so that we can fully utilize appropriate IK/FK control.
Now, open exported file (stickman.fbx) in MB. This model is currently is just mesh and associated bones. To characterize our model...
- in Asset Browser window, click template and character node on left tree, then drag and drop a character entity onto one of joints in our character in 3D workspace.
- popup menu will ask which character model we want to use. Biped or Quadped
(our model is stickman which is bipedal).
- then, MB will add character in our scene. note that "character" means type of entity not indicate our model!
Let's save this file as different name. i.e. stickman_characterized.fbx
4. Motion Data Import
As noted, we will use a few of CMU motion data during our class. The file format we use here is Acclaim ASF/ACM files.
ASF is a definition of subject skeleton(model), and ACM is motion data. ACM should always come together with ASF file. Otherwise, we do not what this motion data is structured.
Followings are very brief steps we need to do. More details will be given during class.
- open ASF file (file / open, then select 16.asf file)
- import motion data: select ACM file(16_15.acm), then MB will ask associated ASF file (select 16.asf again here)
- Import motion option window pops: select merge option
- change take to the first one ("Take 001", This is binding pose)
- characterize this skeleton as similarily as we did for our own model
- save file as something like... walk_motion.fbx
5. Motion Retarget
Refer to EVL mocap tutorial motion builder section for more details of retargetting.
Save retargetted file as something like... stickman_walk_animation.fbx
6. Merge back to Maya scene file
Now, we need to bring back our model into the original scene to export it to Virtools. In fact, we will use our original scene file and exclusively merge motion data (stickman_walk_animation.fbx) into the scene. Main reason for this is we do not want to add any auxilary stuff in our scene. Those extra addition was created while we retargetted motion in MB.
Do following steps.
- open stickman.mb file in maya
- select File / Import menu (set file type to FBX)
- select the motion builder file you saved after retargetting (i.e. stickman_walk_animation.fbx)
- change preset type to Autodesk Motion Builder
- change Include option to update scene
- click import
Then, we get clean animation scene file. You can use this file to export our character model and animation in Virtools format. (refer to virtools manual or week 4 lecture note)
7. Advanced topics
There are much more interesting features and work flow in Motion Builder software. We will cover some of those topics.
- Using Layer to Edit base motion
- Combine two motions (blending) in story mode
- Make nice and clean loop cycle for walk, run, and etc
- Partial blending of multiple motion clips
You can also find some of very useful short tutorial on Autodesk website. Here are some links.
Motion Builder Foundation Learning Tool
Autodesk Area Tutorial section (account required. you can sign in without any charge)