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Statistics of Pose and Shape in Multi-object Complexes Using Principal Geodesic Analysis
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Invited Contributions
Statistics of Pose and Shape in Multi-object Complexes Using Principal Geodesic Analysis
Martin Styner1, 2, Kevin Gorczowski1, Tom Fletcher1, Ja Yeon Jeong1, Stephen M. Pizer1 and Guido Gerig1, 2
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Department of Computer Science, |
| (2) |
Department of Psychiatry, The University of North Carolina, Chapel Hill, NC 27599, |
Abstract
A main focus of statistical shape analysis is the description of variability of a population of geometric objects. In this
paper, we present work in progress towards modeling the shape and pose variability of sets of multiple objects. Principal
geodesic analysis (PGA) is the extension of the standard technique of principal component analysis (PCA) into the nonlinear
Riemannian symmetric space of pose and our medial m-rep shape description, a space in which use of PCA would be incorrect.
In this paper, we discuss the decoupling of pose and shape in multi-object sets using different normalization settings. Further,
we introduce new methods of describing the statistics of object pose using a novel extension of PGA, which previously has
been used for global shape statistics. These new pose statistics are then combined with shape statistics to form a more complete
description of multi-object complexes. We demonstrate our methods in an application to a longitudinal pediatric autism study
with object sets of 10 subcortical structures in a population of 20 subjects. The results show that global scale accounts
for most of the major mode of variation across time. Furthermore, the PGA components and the corresponding distribution of
different subject groups vary significantly depending on the choice of normalization, which illustrates the importance of
global and local pose alignment in multi-object shape analysis.
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