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wip chaikin

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Motiejus Jakštys
2020-06-18 10:38:05 +03:00
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II/Referatas/mj-referatas.tex
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@@ -148,8 +148,14 @@ are often used for line generalization:
\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}.
Review of the available algorithms will be followed by desiderata for a
possible open-source addition. In the end, we will issue a recommendation,
which algorithm can be picked up and implemented by an avid GIS developer.
@@ -251,10 +257,10 @@ a large circle, ilustrated in figure~\ref{fig:blunt-bent}.
\label{fig:blunt-bent}
\end{figure}
Once zoomed in to the river crossing area with {\DP} and {\VW} applied, it becomes apparent that both large
blunts are normalized to single lines, the shape becomes jagged and unpleasant
for the eye. See table~\ref{tab:comparison-crossing} on
page~\pageref{tab:comparison-crossing}.
Once zoomed in to the river crossing area with {\DP} and {\VW} applied, it
becomes apparent that both large blunts are normalized to single lines, the
shape becomes jagged and unpleasant for the eye. See
table~\ref{tab:comparison-crossing} on page~\pageref{tab:comparison-crossing}.
\begin{figure}[h]
\renewcommand{\tabularxcolumn}[1]{>{\center\small}m{#1}}
@@ -280,6 +286,31 @@ page~\pageref{tab:comparison-crossing}.
\label{tab:comparison-crossing}
\end{figure}
As the reader may observe, the output lines, especially with higher tolerances,
are jaggy. Higher-tolerance jaggy outputs from {\VW} and {\DP}, passed through Chaikin,
are displayed in table~\ref{tab:chaikin-crossing} on
page~\page{tab:chaikin-crossing}.
\begin{figure}[h]
\renewcommand{\tabularxcolumn}[1]{>{\center\small}m{#1}}
\begin{tabularx}{\textwidth}{ p{2.1cm} | X | X | }
Tolerance DP/VW &
Douglas \& Peucker &
Visvalingam-Whyatt \tabularnewline \hline
128/16384 &
\includegraphics[width=\linewidth]{chaikin_overlaid_zeimena_douglas_128} &
\includegraphics[width=\linewidth]{chaikin_overlaid_zeimena_visvalingam_128} \tabularnewline \hline
256/65536 &
\includegraphics[width=\linewidth]{chaikin_overlaid_zeimena_douglas_256} &
\includegraphics[width=\linewidth]{chaikin_overlaid_zeimena_visvalingam_256} \tabularnewline \hline
\end{tabularx}
\caption{Chaikin-smoothened {\DP} and {\VW} on river crossing area}
\label{tab:chaikin-crossing}
\end{figure}
There is another issue on the wishlist beyond jaggyness and loss of large bents
-- combining close bends to larger ones.