expand on VW and DP deficiencies
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\title{
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\includegraphics[width=60mm]{vu.png}\\[8ex]
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Cartographic Generalization of Lines using free software \\
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(example of rivers) \\ \vspace{4mm}
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(example of rivers)
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}
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\author{Motiejus Jakštys}
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@ -45,11 +45,11 @@
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}
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\begin{document}
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\maketitle
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\clearpage\maketitle
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\thispagestyle{empty}
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\begin{abstract}
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\label{sec:abstract}
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Current open-source line generalization solutions have their roots in
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mathematics and geometry, and are not fit for natural objects like rivers
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and coastlines. This paper discusses our implementation of {\WM} algorithm
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@ -116,15 +116,34 @@ The "classical" ones are {\DP} and {\VW}.
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\cite{douglas1973algorithms} and \cite{visvalingam1993line} are "classical"
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line generalization computer graphics algorithms. They are relatively simple to
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implement, require few runtime resources. Both of them accept only a single
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parameter, which makes them very simple to adjust for different scales.
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parameter, based on desired scale of the map, which makes them very simple to
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adjust for different scales.
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However, both of them are emitting insufficient
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Both algorithms are part of PostGIS, a free-software GIS suite:
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\begin{itemize}
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\item \cite{douglas1973algorithms} via
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\href{https://postgis.net/docs/ST_Simplify.html}{PostGIS Simplify}.
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\item \cite{visvalingam1993line} via
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\href{https://postgis.net/docs/ST_SimplifyVW.html}{PostGIS SimplifyVW}.
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\end{itemize}
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Since both algorithms produce jagged output lines, it is worthwhile to process
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those through a widely available \cite{chaikin1974algorithm} smoothing
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algorithm via \href{https://postgis.net/docs/ST_ChaikinSmoothing.html}{PostGIS
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ChaikinSmoothing}.
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Even though {\DP} and {\VW} are simple to understand and computationally
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efficient, they have serious deficiencies for cartographic natural line
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generalization.
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<TODO: expand on deficiencies>
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\subsection{Modern approaches}
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After {\DP} and {\VW} have been established,
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These fall into two rough categories:
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Due to their simplicity and ubiquity, {\DP} and {\VW} have been established as
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go-to algorithms for line generalization. During recent years, more modern
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replacement algorithms have emerged. These fall into roughly two categories:
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\begin{itemize}
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\item Cartographic knowledge was encoded to an algorithm (bottom-up
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@ -134,35 +153,20 @@ These fall into two rough categories:
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\cite{mustafa2006dynamic}, \cite{nollenburg2008morphing}.
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\end{itemize}
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During research for the mentioned articles, prototype code has been written for
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most of the algorithms. However, none of them seem to be available for use
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except for the two "classical" ones -- {\DP} and {\VW}.
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Authors of most of the aforementioned articles have implemented the
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generalization algorithm, at least to generate the visuals in the articles.
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However, I wasn't able to find code for any of those to evaluate with my
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desired data set, or use as a basis for my own maps. \cite{wang1998line} is
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available in a commercial product.
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\cite{wang1998line} is an algorithm specifically created for cartographic
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generalization and available for general use, though it is only currently
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available in a commercial product. This poses a problem for map creation in
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open source software: there is not a similar high-quality simplification
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algorithm to create down-scaled maps, so any cartographic work, which uses line
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generalization as part of its processing, will be of sub-par quality.
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We believe that availability of high-quality open-source tools is an important
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foundation for future cartographic experimentation and development, thus it
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it benefits the cartographic society as a whole.
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This paper will be reviewing and comparing two widely available algorithms that
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are often used for line generalization:
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\begin{itemize}
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\item \cite{douglas1973algorithms} via
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\href{https://postgis.net/docs/ST_Simplify.html}{PostGIS Simplify}.
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\item \cite{visvalingam1993line} via
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\href{https://postgis.net/docs/ST_SimplifyVW.html}{PostGIS SimplifyVW}.
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\end{itemize}
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Since both algorithms produce jaggy output lines, it is worthwhile to process
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those through a widely available \cite{chaikin1974algorithm} smoothing
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algorithm via \href{https://postgis.net/docs/ST_ChaikinSmoothing.html}{PostGIS
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ChaikinSmoothing}.
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The lack of robust openly available generalization algorithm implementations
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poses a problem for map creation with free software: there is not a similar
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high-quality simplification algorithm to create down-scaled maps, so any
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cartographic work, which uses line generalization as part of its processing,
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will be of sub-par quality. We believe that availability of high-quality
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open-source tools is an important foundation for future cartographic
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experimentation and development, thus it it benefits the cartographic society
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as a whole.
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\section{Methodology}
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\label{sec:methodology}
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