Y.Liu, R.Collins and Y.Tsin,
"Gait Sequence Analysis using Frieze Patterns,"
European Conference on Computer Vision,
Copenhagen, May 2002, pp.657-671. Also,
Technical Report CMU-RI-TR-01-38, Robotics Institute, 
Carnegie Mellon University, December, 2001.


We analyze walking people using a gait sequence representation that bypasses the need for frame-to-frame tracking of body parts. The gait representation maps a video sequence of silhouettes into a pair of two-dimensional spatio-temporal patterns that are periodic along the time axis. Mathematically, such patterns are called "frieze" patterns and associated symmetry groups "frieze groups". With the help of a walking humanoid avatar, we explore variation in gait frieze patterns with respect to viewing angle, and find that the frieze groups of the gait patterns and their canonical tiles enable us to estimate viewing direction. In addition, analysis of periodic patterns allows us to determine the dynamic time warping and affine scaling that aligns two gait sequences from similar viewpoints. We show how gait alignment can be used to perform human identification and model-based body part segmentation.

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