[ut.dcs.seminars] Dave Forsey, 6 March 1990: GRAPHICS & INTERACTION

edith@ai.toronto.edu (Edith Fraser) (02/27/90)

                            FLASH ANNOUNCEMENT
              (GB = Galbraith Building, 35 St. George Street)


                          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