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Shape deformation analysis from the optimal control viewpoint
A crucial problem in shape deformation analysis is to determine a deformation
of a given shape into another one, which is optimal for a certain cost. It has
a number of applications in particular in medical imaging. In this article we
provide a new general approach to shape deformation analysis, within the
framework of optimal control theory, in which a deformation is represented as
the flow of diffeomorphisms generated by time-dependent vector fields. Using
reproducing kernel Hilbert spaces of vector fields, the general shape
deformation analysis problem is specified as an infinite-dimensional optimal
control problem with state and control constraints. In this problem, the states
are diffeomorphisms and the controls are vector fields, both of them being
subject to some constraints. The functional to be minimized is the sum of a
first term defined as geometric norm of the control (kinetic energy of the
deformation) and of a data attachment term providing a geometric distance to
the target shape. This point of view has several advantages. First, it allows
one to model general constrained shape analysis problems, which opens new
issues in this field. Second, using an extension of the Pontryagin maximum
principle, one can characterize the optimal solutions of the shape deformation
problem in a very general way as the solutions of constrained geodesic
equations. Finally, recasting general algorithms of optimal control into shape
analysis yields new efficient numerical methods in shape deformation analysis.
Overall, the optimal control point of view unifies and generalizes different
theoretical and numerical approaches to shape deformation problems, and also
allows us to design new approaches. The optimal control problems that result
from this construction are infinite dimensional and involve some constraints,
and thus are nonstandard. In this article we also provide a rigorous and
complete analysis of the infinite-dimensional shape space problem with
constraints and of its finite-dimensional approximations
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