From 32e125ff550dbe7f93d2752a0f4732bd1d98a4d7 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Motiejus=20Jak=C5=A1tys?= Date: Wed, 19 May 2021 22:57:46 +0300 Subject: [PATCH] expand on VW and DP deficiencies --- mj-msc.tex | 76 ++++++++++++++++++++++++++++-------------------------- 1 file changed, 40 insertions(+), 36 deletions(-) diff --git a/mj-msc.tex b/mj-msc.tex index 186e595..47c0536 100644 --- a/mj-msc.tex +++ b/mj-msc.tex @@ -35,7 +35,7 @@ \title{ \includegraphics[width=60mm]{vu.png}\\[8ex] Cartographic Generalization of Lines using free software \\ - (example of rivers) \\ \vspace{4mm} + (example of rivers) } \author{Motiejus Jakštys} @@ -45,11 +45,11 @@ } \begin{document} -\maketitle +\clearpage\maketitle +\thispagestyle{empty} \begin{abstract} \label{sec:abstract} - Current open-source line generalization solutions have their roots in mathematics and geometry, and are not fit for natural objects like rivers and coastlines. This paper discusses our implementation of {\WM} algorithm @@ -116,15 +116,34 @@ The "classical" ones are {\DP} and {\VW}. \cite{douglas1973algorithms} and \cite{visvalingam1993line} are "classical" line generalization computer graphics algorithms. They are relatively simple to implement, require few runtime resources. Both of them accept only a single -parameter, which makes them very simple to adjust for different scales. +parameter, based on desired scale of the map, which makes them very simple to +adjust for different scales. -However, both of them are emitting insufficient +Both algorithms are part of PostGIS, a free-software GIS suite: +\begin{itemize} + \item \cite{douglas1973algorithms} via + \href{https://postgis.net/docs/ST_Simplify.html}{PostGIS Simplify}. + + \item \cite{visvalingam1993line} via + \href{https://postgis.net/docs/ST_SimplifyVW.html}{PostGIS SimplifyVW}. +\end{itemize} + +Since both algorithms produce jagged output lines, it is worthwhile to process +those through a widely available \cite{chaikin1974algorithm} smoothing +algorithm via \href{https://postgis.net/docs/ST_ChaikinSmoothing.html}{PostGIS +ChaikinSmoothing}. + +Even though {\DP} and {\VW} are simple to understand and computationally +efficient, they have serious deficiencies for cartographic natural line +generalization. + + \subsection{Modern approaches} -After {\DP} and {\VW} have been established, - -These fall into two rough categories: +Due to their simplicity and ubiquity, {\DP} and {\VW} have been established as +go-to algorithms for line generalization. During recent years, more modern +replacement algorithms have emerged. These fall into roughly two categories: \begin{itemize} \item Cartographic knowledge was encoded to an algorithm (bottom-up @@ -134,35 +153,20 @@ These fall into two rough categories: \cite{mustafa2006dynamic}, \cite{nollenburg2008morphing}. \end{itemize} -During research for the mentioned articles, prototype code has been written for -most of the algorithms. However, none of them seem to be available for use -except for the two "classical" ones -- {\DP} and {\VW}. +Authors of most of the aforementioned articles have implemented the +generalization algorithm, at least to generate the visuals in the articles. +However, I wasn't able to find code for any of those to evaluate with my +desired data set, or use as a basis for my own maps. \cite{wang1998line} is +available in a commercial product. -\cite{wang1998line} is an algorithm specifically created for cartographic -generalization and available for general use, though it is only currently -available in a commercial product. This poses a problem for map creation in -open source software: there is not a similar high-quality simplification -algorithm to create down-scaled maps, so any cartographic work, which uses line -generalization as part of its processing, will be of sub-par quality. -We believe that availability of high-quality open-source tools is an important -foundation for future cartographic experimentation and development, thus it -it benefits the cartographic society as a whole. - -This paper will be reviewing and comparing two widely available algorithms that -are often used for line generalization: -\begin{itemize} - \item \cite{douglas1973algorithms} via - \href{https://postgis.net/docs/ST_Simplify.html}{PostGIS Simplify}. - - \item \cite{visvalingam1993line} via - \href{https://postgis.net/docs/ST_SimplifyVW.html}{PostGIS SimplifyVW}. - -\end{itemize} - -Since both algorithms produce jaggy output lines, it is worthwhile to process -those through a widely available \cite{chaikin1974algorithm} smoothing -algorithm via \href{https://postgis.net/docs/ST_ChaikinSmoothing.html}{PostGIS -ChaikinSmoothing}. +The lack of robust openly available generalization algorithm implementations +poses a problem for map creation with free software: there is not a similar +high-quality simplification algorithm to create down-scaled maps, so any +cartographic work, which uses line generalization as part of its processing, +will be of sub-par quality. We believe that availability of high-quality +open-source tools is an important foundation for future cartographic +experimentation and development, thus it it benefits the cartographic society +as a whole. \section{Methodology} \label{sec:methodology}