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\def\real   {{\rm I\kern-.2em R}} 
\def\espace {\rm I\kern-.2em E} 
\def\FUN    {f}          % function describing a terrain
\def\NODE   {N}          % MT node 
\def\THR    {\tau}       % threshold function
\def\FCS    {{\cal F}}   % focus set
\def\BOUND  {b}          % bound on degree of removable vertices
\def\UPD    {C}          % mesh update
\def\MM     {{\cal M}}   % DAG of the multiresolution model
\def\THR    {\tau}       % threshold function
\def\FCS    {I}          % focus set, qui chiamata region of interest
\def\TD     {{TD}}       % top down
\def\BU     {{BU}}       % bottom up

\def\NOTA #1 {}

\begin{article}
\begin{opening}         


\title{
VARIANT:
A System for Terrain Modeling at Variable Resolution
}

\author{
Leila De Floriani, Paola Magillo, Enrico Puppo
}

\runningauthor{De Floriani, Magillo, Puppo}
\runningtitle{VARIANT}

\institute{
Dipartimento di Informatica e Scienze dell'Informazione\\
Universit\`a di Genova\\
Via Dodecaneso, 35 -- 16146 Genova (Italy)\\
Email: \{deflo,magillo,puppo\}@disi.unige.it
}

\date{\today}

\begin{abstract}
We describe VARIANT (VAriable Resolution Interactive ANalysis of Terrain), 
an extensible system for processing and visualizing terrain represented
with TINs, featuring the accuracy of representation, possibly
variable over the terrain domain, as a further parameter in computation.

VARIANT is based on a multiresolution terrain model, 
%called a Multi-Triangulation (MT), 
which we developed in our earlier research.
%\cite{Pup96,DeFMagPupIEEE98,Mag99}.
%, and it is implemented upon an object
%oriented library for managing the MT \cite{MagDeFPup00}.
Its architecture is made of a kernel, which provides
primitive operations for building and querying the multiresolution model;
and of application programs, which access a terrain model based on
the primitives in the kernel. 

VARIANT directly supports basic queries (e.g., windowing, buffering,
computation of elevation at a given point, or along a given line)
as well as high level operations (e.g., viewshed analysis, contour map 
extraction, fly-over visualization). 
But the true power of VARIANT is the possibility to extend it with 
new applications
that can exploit its multiresolution features in a transparent way.  
\NOTA{
Control over resolution is achieved by defining threshold conditions to set
desired accuracy, and focus conditions to select either regions of interest 
or interesting entities on the domain. Such conditions can be easily 
customized to application needs.
}
\end{abstract}

\keywords{Terrain Modeling, Multiresolution Structures, Level of Detail,
Query Operations.}

\end{opening}           

\input{part1}

\input{part2}

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\acknowledgements

This work has been partially supported by the project
``A Library for Applications in Geometric Modeling'' and
by the project ``Systems for Geometric Modeling'' of the
Italian National Research Council.
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% \appendix{}


\input{refs}

\end{article}
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