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