mirror of https://github.com/CGAL/cgal
70 lines
2.6 KiB
TeX
70 lines
2.6 KiB
TeX
Subdivision algorithms contain two major
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components: \emph{\tr} and \emph{\gm}.
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The \tr\ reparameterizes the source mesh into the target
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mesh. The \gm\ transforms a submesh on the source mesh
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to a vertex on the refined mesh. The source submesh with
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the normalized weighting is called
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\emph{stencil}. A proper combination of a \tr\ and a set of
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rules of \gm\ define a valid subdivision scheme.
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Figure \ref{fig:RefSchemes} shows the local configuration
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of four major refinements
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employed in subdivision algorithms, which include Catmull-Clark
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subdivision (PQQ) \cite{cc}, Loop subdivision (PTQ) \cite{loop},
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Doo-Sabin subdivision (DQQ) \cite{ds} and $\sqrt{3}$ subdivision
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\cite{sqrt3}. Subdivisions, such as Quad-Triangle subdivision (PQQ and
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PTQ) \cite{qts,l-pg-03}, may employ a hybrid refinement consisting
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of two different refinements.
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\begin{figure}
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\centering
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\psfrag{PQQ}[]{\scriptsize PQQ}
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\psfrag{PTQ}[]{\scriptsize PTQ}
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\psfrag{DQQ}[]{\scriptsize DQQ}
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\psfrag{Sqrt3}[]{\scriptsize $\sqrt{3}$}
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\epsfig{file=figs/RefSchemes.eps, width=7cm}
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\caption{Topology refinements:
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primal quadrilateral quadrisection (PQQ),
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primal triangle quadrisection (PTQ),
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dual quadrilateral quadrisection (DQQ) and
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$\sqrt{3}$ triangulation.}
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\label{fig:RefSchemes}
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\end{figure}
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The \gm\ applies a \emph{mask} on the stencil and
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generate the corresponding vertex on the refined mesh.
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The mask usually specifies an affine combination of the
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stencil. Figure \ref{fig:RefMap} demonstrates the examples of the
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correspondence between a stencil and its vertex. Subdivisions
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usually have distinct masks associated with different stencils
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(Figure \ref{fig:RefMap} (a-c)).
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\begin{figure}
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\centering
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\psfrag{A}[]{(a)}
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\psfrag{B}[]{(b)}
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\psfrag{C}[]{(c)}
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\psfrag{D}[]{(d)}
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\epsfig{file=figs/RefMap.eps, width=7cm}
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\caption{The stencil and its vertex in the
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Catmull-Clark subdivision (a-c)
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and Doo-Sabin subdivision (d). Catmull-Clark
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subdivision has three stencils: facet-stencil (a),
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edge-stencil (b) and vertex-stencil (c).
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Doo-Sabin subdivision has only corner-stencil (d).}
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\label{fig:RefMap}
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\end{figure}
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% templated rules: a generic framework for subdivisions
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%\subsection{Generic Subdivisions}
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%\label{sec:subtempl}
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\input subtempl
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\subsection{Sqrt 3}
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% connectivity ops: specific polyhedron algorithms (sqrt3 subdivisions)
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%\subsection{$\sqrt{3}$-Subdivision using Euler Operators}
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\input sqrt3
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% inc builder: specific polyhedron algorithms (qt subdivisions)
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%\subsection{Quad-triangle Subdivision using modifier}
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%\input qt
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