commit 8b6af72d72e78da75d0e2a24dc31b93e4d49321f (tree)
parent 50d0afdef72a44a922c2733f92ccffa46e4e8e30
Author: Motiejus Jakštys <motiejus@uber.com>
Date: Thu, 29 Apr 2021 16:51:30 +0300
problem areas
Diffstat:
1 file changed, 31 insertions(+), 12 deletions(-)
diff --git a/IV/mj-msc.tex b/IV/mj-msc.tex
@@ -48,7 +48,7 @@
\newcommand{\DP}{Douglas \& Peucker}
\newcommand{\VW}{Visvalingam--Whyatt}
\newcommand{\WM}{Wang--M{\"u}ller}
-% {\WM} algoritmo realizacija kartografinei upių generalizacijai vykdyti (PostGIS programinės įrangos pagrindu)
+% {\WM} algoritmo realizacija kartografinei upių generalizacijai
\newcommand{\MYTITLE}{{\WM} algorithm realization for cartographic line generalization}
\newcommand{\MYAUTHOR}{Motiejus Jakštys}
@@ -80,12 +80,15 @@
\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}'s algorithm
- under and open-source license, explains things that we would had
- appreciated in the original paper and compares our results to different
- generalization algorithms.
+
+Currently available line simplification algorithms are rooted in mathematics
+ and geometry, and are not fit bendy natural features like rivers and
+ coastlines. This paper discusses our implementation of {\WM} algorithm,
+ with notes that we would have been appreciated before starting the
+ re-implementation endeavor. This paper accompanies our implementation of
+ {\WM} algorithm and will be helpful to anyone trying to understand the
+ original {\WM} paper, or our implementation.
+
\end{abstract}
\newpage
@@ -268,18 +271,34 @@ figure~\onpage{fig:salvis-generalized-chaikin-50k}.
\label{fig:salvis-overlaid-generalized-chaikin-50k}
\end{figure}
-There are a few problems with {\VW} and {\DP} immediately visible in
-figure~\onpage{fig:salvis-generalized-chaikin-50k}:
+The resulting generalized and smoothened example
+(figure~\onpage{fig:salvis-generalized-chaikin-50k}) yields a more
+aesthetically pleasant result, however, it obscures natural river features.
+Given the absence of rocks, the only natural features that influence the river
+direction are topographic:
\begin{itemize}
- \item problem 1
- \item problem 2
+
+ \item Relatively straight river (completely straight or with small-angled
+ bends over a relatively long distance) implies greater slope, more
+ water, and/or faster flow.
+
+ \item Bendy river, on the contrary, implies slower flow, smaller slope,
+ and/or less water.
+
\end{itemize}
-Therefore, a more robust generalization algorithm is worthwhile for lookout.
+Both {\VW} and {\DP} have a tendency to remove the small bends altogether,
+which is a valuable characterization of the river. Therefore, a more robust
+generalization algorithm is worthwhile for lookout.
\subsubsection{Modern approaches}
+% TODO:
+% https://pdfs.semanticscholar.org/e80b/1c64345583eb8f7a6c53834d1d40852595d5.pdf
+% A New Algorithm for Cartographic Simplification of Streams and Lakes Using
+% Deviation Angles and Error Bands
+
Due to their simplicity and ubiquity, {\DP} and {\VW} have been established as
go-to algorithms for line generalization. During recent years, alternatives
have emerged. These modern replacements fall into roughly two categories:
