Eva Schiffer

Analyzing the Physical Correctness of Interpolated Human Motion
by Alla Safonova and Jessica Hodgins 

Summary:

This paper analyses the correctness of interpolated motion in terms of basic physics and suggests several possible improvements which could be made on traditional interpolation schemes in order to improve physical correctness. 

Problem:

When do interpolated motions, which are formed from two "correct" motions, end up being physically impossible? What can be done to improve these basic physics related problems?

Method:

The paper examines theoretically properties of motions formed by simple linear blending and tries to discover when they will be systematically physically incorrect. Various stages of the motion are considered, including the flight phase, the phase when the character is on the ground, and when the character is transitioning between the ground and flight. Special focus is given to some physical properties such as linear momentum, angular momentum, foot contact, balance, and friction cone. 

Key Ideas:

Simple linear blending interpolation does a poor job of blending foot contact, flight phases with different axes of rotation,  warping time during flight.

Contributions:

Three improvements to standard linear weighted blends were suggested in order to improve overall physical correctness. 
Cases where blending motions, such as flight with differing axes of rotation, will not work well are identified.

Questions:

I am curious how much of an effect the changes described here have on foot skate.