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Motiejus Jakštys 2021-05-15 23:17:39 +03:00
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@ -1312,9 +1312,9 @@ implementation. A single exaggeration increment is done as follows:
is linearly interpolated between $[s,1]$, using the same rules as for is linearly interpolated between $[s,1]$, using the same rules as for
the first half. the first half.
The first version of the algorithm used simple linear interpolation based The first version of the algorithm used simple linear interpolation
on the point's position in the line. The current version applies a few based on the point's position in the line. The current version applies
coefficients, which were derived empirically, by observing the a few coefficients, which were derived empirically, by observing the
resulting bend. resulting bend.
\item Each point (except the beginning and end vertices of the bend) will \item Each point (except the beginning and end vertices of the bend) will
@ -1323,9 +1323,6 @@ implementation. A single exaggeration increment is done as follows:
\end{enumerate} \end{enumerate}
Figure~\ref{fig:isolated-1-exaggerated} illustrates an exaggerated bend with
the algorithm.
\begin{figure}[ht] \begin{figure}[ht]
\centering \centering
\includegraphics[width=.5\textwidth]{isolated-1-exaggerated} \includegraphics[width=.5\textwidth]{isolated-1-exaggerated}
@ -1333,6 +1330,24 @@ the algorithm.
\label{fig:isolated-1-exaggerated} \label{fig:isolated-1-exaggerated}
\end{figure} \end{figure}
The technical implementation of the algorithm contains two implementations
of exaggeration operator:
\begin{description}
\item[\normalfont\textsc{wm\_exaggerate\_bend}] is the original one. It
uses simple linear interpolation. It is fast, but simple. It tends to
leave jagged bends.
\item[\normalfont\textsc{wm\_exaggerate\_bend2}] is a more computationally
expensive function, which leaves better-looking exaggerated bends.
\end{description}
Both functions are inter-change-able and can be found in listing~\ref{lst:wm.sql}.
Figure~\ref{fig:isolated-1-exaggerated} illustrates an exaggerated bend using
\textsc{wm\_exaggerate\_bend2}.
\section{Results} \section{Results}
\label{sec:results} \label{sec:results}
@ -1349,8 +1364,7 @@ table~\ref{table:scale-halfcirlce-diameter}:
\item 1:\numprint{250000}: 220. \item 1:\numprint{250000}: 220.
\end{itemize} \end{itemize}
The original feature is orange. As can be seen, some isolated bends are \subsubsection{Medium-scale (1:\numprint{50000})}
exaggerated, and some small bends are removed.
\begin{figure}[ht] \begin{figure}[ht]
\centering \centering
@ -1368,11 +1382,15 @@ exaggerated, and some small bends are removed.
\label{fig:salvis-wm-50k} \label{fig:salvis-wm-50k}
\end{figure} \end{figure}
As one can see in figure~\ref{fig:salvis-wm-50k}, some of the small bends have As one can see in figure~\ref{fig:salvis-wm-50k}, the illustrations deliver
been exaggerated, and some removed. It mostly works as expected, except some of what was promised by the algorithm, but with a few caveats. West-side of the
the jagged lines approximately in the middle of the figure. river looks reasonably well simplified: long bends remain slightly curved,
small bends are removed or slightly exaggerated.
Approximately at the middle of the figure some jagged and sharp bends appear.
Figure~\ref{fig:salvis-wm-50k-overlaid-zoom} zooms in, overlaying the original Figure~\ref{fig:salvis-wm-50k-overlaid-zoom} zooms in, overlaying the original
river (in orange). river (in orange). These will become more pronounced in even larger-scale
simplification in the next section.
\begin{figure}[ht] \begin{figure}[ht]
\centering \centering
@ -1381,12 +1399,6 @@ river (in orange).
\label{fig:salvis-wm-50k-overlaid-zoom} \label{fig:salvis-wm-50k-overlaid-zoom}
\end{figure} \end{figure}
These will become
more pronounced in large-scale simplification in the next section. Other than
some sharp edges, this algorithm works reasonably well for mid-scale
simplification.
\subsubsection{Large-scale (1:\numprint{250000})} \subsubsection{Large-scale (1:\numprint{250000})}
As visible in figure~\ref{fig:salvis-wm-250k}, for large-scale map, some of the As visible in figure~\ref{fig:salvis-wm-250k}, for large-scale map, some of the
@ -1421,8 +1433,8 @@ simplification and overlays the original (in orange).
A conglomeration of bends is visible, especially in north-east side of the A conglomeration of bends is visible, especially in north-east side of the
center. We assume this was caused by two bends significantly exaggerated, center. We assume this was caused by two bends significantly exaggerated,
leaving no space to exaggerate for those between the two. For the same reason, leaving no space to exaggerate for those between the two. For the same reason,
the 1:\numprint{50000} figure~\ref{fig:salvis-wm-50k} has many smaller bends the figure~\ref{fig:salvis-wm-50k} (of scale 1:\numprint{50000}) has many
at approximately the same location. smaller bends at approximately the same location.
\subsection{Comparison of Generalization Result with National Spatial Datasets} \subsection{Comparison of Generalization Result with National Spatial Datasets}