edith@ai.toronto.edu (Edith Fraser) (02/27/90)
FLASH ANNOUNCEMENT
(GB = Galbraith Building, 35 St. George Street)
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GRAPHICS & INTERACTION
GB220, at 3:00 p.m., 6 March 1990
Dave Forsey
University of Waterloo
"Here There Be Dragons"
A tensor-product spline surface consists of an M by N array of control
vertices that define an array of piecewise polynomial patches joined with
specified continuity at the patch boundaries. Classically, the number
of patches in such a surface is increased through knot insertion, which
adds either an entire row or column to the array of control vertices ;
splitting all the patches along an entire row or column of the
surface. Since patches cannot be added locally, as the number of
patches in the surface increase, knot insertion becomes increasing costly
due to the addition of control vertices and patches to regions where they
are not necessarily needed. This property is particularly a problem in
modelling surfaces, such as human or animal bodies, where regions of
vastly differing detail are part of the same surface.
This talk discusses hierarchical free-form surfaces, a data structuring
technique that allows local refinement of a tensor-product spline surface
so that the number of patches in a given region can be increased
without affecting the rest of the surface.
This formulation has useful applications in spline representation and
storage, surface editing, animation, and data fitting. A brief video will
be presented demonstrating a prototype editor for hierarchical B-splines,
and includes an animation whose central character was created using that
editor.