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A Quick Introduction to Motion Editing:

What is Motion Editing?

    Most animated motions, no matter what source they come from, are very specific: they apply to a specific character, performing a specific action, in a specific way. For example, if we have motion for a tall female character angrily pulling open a door, we do not have a motion for anything else, such as a different (e.g. shorter) character, in a different (e.g. happy or excited) mood, doing a different action (e.g. pulling open a door). We also cannot have a different door.

    Motion editing allows us to alter a motion; to change some (or many) aspects of a motion such that we can re-use it.

Why Edit Motion?

    The special-purposeness mentioned above limits the utility of animated motion. By being able to change a motion after it's created, we don't need to have exactly the right motion on the first try. This enables:

  • Re-use of motion assets (because good motion is so hard to make, we want to be able to use it again and again).
  • Increased worth of motion capture data (because you rarely can capture exactly what you are looking for).
  • Non-animators to make animation (because its easier to beg, borrow, copy, steal or buy than to create from scratch).
  • Animators to be more responsive (when the demands of a production change from the original specification).
  • Dynamic motion applications, such as games (where the needs aren't known ahead of time).

    We see motion editing evolving as a paradigm for creating motion. Initially motion editing was a tool for tweaking motions created by some "more traditional" method of motion creation. We now consider making new motions by adapting, understanding, and manipulating existing sets.

Why is motion editing difficult?

    Animation is difficult in general. Since animation relies on motion to set it apart from other mediums, it is imperative that it is done well.

    Because specifying motion is so uncommon, few people have developed the skill to do it, let alone understand it or describe it (there hardly exists a vocabulary for the purpose). While most people might pick up a crayon and start drawing at a very young age, few ever turn their creativity into motion until they become animators. Our language provides precise, detailed mechanisms for specifying geometry and form, however, commonly used language lacks equivalent terms for motion.

    What this means is that while motion is often self-evident, it is very difficult to describe in a concise way. While geometric descriptions are easily recreated (e.g. a 3 inch green square), motion rarely can be described in such detail. Typically motion must be described in terms of results, metaphors, and moods. We are reduced to talking about a happy or sad motion, a motion that lifts a box to the shelf, a regal march, or something similarly vague.

    The question then arises; if you want to change a motion, how do you describe what you have, what you want, what you want to change, what you don't want to change, etc. Furthermore, how do you describe that in a mathematical way (since that's all computers can understand). This fundamental communication is the crux of what makes motion editing difficult.

How do you Edit Motion?

    Funny you should ask....
    We have been developing various techniques for motion editing over the past few years. We have been attacking a number of motion editing problems (e.g. things we want to change about motions) using an expanding toolbox of tricks. Our techniques have been aimed to be general across many problems. Specifically, we have been focussing on a constraint-based approach in which geometric features in one motion are identified and are maintained in subsequent manipulated motions.

    We are not the only ones exploring motion editing, and our methods are not the only ones out there. In addition to our efforts to invent new techniques, we have been trying to help people understand motion editing in general - which is exactly why we put together this web site. Partially to advertize our stuff, but mostly to educate people about motion editing.

Where can I learn more about motion editing?

    You've come to the right place!

    The motion editing group is collecting information about motion editing on this very page. You can find information about our projects, our software system, our papers, our results (movies), or even UW Madison's entire graphics group.

    We have some general tutorial information (including SIGGRAPH course notes on the subject), and links to other resources. You might also want to look at the animation courses taught here at UW, since we also spend time on motion editing there.

    We have set up a mailing list for people to discuss motion editing. The list is generally very low traffic, so if you have any interest, you might want to try it out.

Introduction

Papers

Approach
  types of constraints

Software Infrastructure

Techniques
  motion retargeting
  path-editing

Downloads

Mailing List

SIGGRAPH
course notes

Related links