test harness
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bib.bib
21
bib.bib
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@ -228,3 +228,24 @@
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url={https://github.com/motiejus/wm},
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urldate={2021-05-19},
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}
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@online{openstreetmap,
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author={OpenStreetMap contributors},
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title={Project that creates and distributes free world's geographic data},
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url={https://www.openstreetmap.org},
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urldate={2021-05-15},
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}
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@online{nzt,
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author={Nacionalinė Žemės Tarnyba Prie Žemės Ūkio Ministerijos},
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title={Atviri Duomenys},
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url={http://nzt.lt/go.php/lit/Atviri-duomenys},
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urldate={2021-05-15},
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}
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@online{openmapwm,
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author={Tomas Straupis},
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title={Test harness for Wang--M{\"u}ller algorithm},
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url={https://dev.openmap.lt/webgl/wm.html},
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urldate={2021-05-15},
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}
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49
mj-msc.tex
49
mj-msc.tex
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@ -909,11 +909,20 @@ When debug mode is turned off (that is, \textsc{dbgname} is left unspecified),
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\subsection{Merging pieces of the river into one}
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% TODO
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Example river geometries were sourced from OpenStreetMap\cite{openstreetmap}
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and NŽT\cite{nzt}. Rivers in both data sources are stored in shorter line
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segments, and multiple segments (usually hundreds or thousands for significant
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rivers) define one full river. While it is convenient to store and edit, these
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segments are not explicitly related to each other. This poses a problem for
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simplification algorithms, which manipulate on full linear features at a time:
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full river geometries, but not their parts.
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NOTE: explain how different river segments are merged into a single line. This
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is not explained in the {\WM} paper, but is a necessary prerequisite. This is
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implemented in \textsc{aggregate-rivers.sql}.
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Since these rivers do not have an explicit relationship to connect them
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together, they were connected using heuristics: if two line segments share a
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name and are within 500 meters from each other, then they form a single river.
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For all line simplification algorithms, all rivers need to be combined, and
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this way proved to be reasonably effective. Source code for this operation can
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be found in listings~\onpage{lst:aggregate-rivers.sql}.
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\subsection{Bend scaling and dimensions}
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\label{sec:bend-scaling-and-dimensions}
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@ -1002,7 +1011,7 @@ but with bends colored as polygons: each color is a distinctive bend.
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\centering
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\includegraphics[width=\textwidth]{fig8-definition-of-a-bend}
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\caption{similar to figure 8 in \cite{wang1998line}: detected bends are
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\caption{Similar to figure 8 in \cite{wang1998line}: detected bends are
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highlighted.}
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\label{fig:fig8-definition-of-a-bend}
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@ -1031,7 +1040,7 @@ when a single vertex is moved outwards the end of the bend.
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\includegraphics[width=\textwidth]{fig5-gentle-inflection-after}
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\caption{After applying the inflection rule.}
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\end{subfigure}
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\caption{figure 5 in \cite{wang1998line}: gentle inflections at the ends of
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\caption{Figure 5 in \cite{wang1998line}: gentle inflections at the ends of
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the bend.}
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\label{fig:fig5-gentle-inflection}
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\end{figure}
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@ -1347,7 +1356,8 @@ isolated bends are exaggerated, and some small bends are removed.
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\label{fig:salvis-wm-220-250k}
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\end{figure}
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% TODO: expand
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% TODO: expand section and remove clear-page.
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\clearpage
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\subsection{Generalization result comparison with national spatial data sets}
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@ -1355,9 +1365,28 @@ isolated bends are exaggerated, and some small bends are removed.
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\subsection{Testing results online}
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% TODO: [Siūlau įdėti nuorodą į web app, kur būtų galima interaktyviai
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% pastestuoti rezultatus. Jeigu planuotum dėti, tuomet galima nedidelį poskyrį
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% pridėti Testing Results]
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An on-line tool\cite{openmapwm} has been developed to test incoming parameters
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to {\WM} algorithm. A user should select a river of interest, enter the
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\textsc{dhalfcircle} parameter and click "Submit". The simplified line feature
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will be overlaid on top of the map.
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Figure~\ref{fig:openmap-wm-good} illustrates the end result that looks
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reasonably well. Figure~\ref{fig:openmap-wm-bad} illustrates that the algorithm
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produces poorly simplified results for some geometries.
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\begin{figure}[ht]
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\centering
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\includegraphics[width=\textwidth]{openmap-wm-good.png}
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\caption{Example on-line test tool for {\WM} algorithm.}
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\label{fig:openmap-wm-good}
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\end{figure}
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\begin{figure}[ht]
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\centering
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\includegraphics[width=.5\textwidth]{openmap-wm-bad.png}
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\caption{Another example from the on-line test tool.}
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\label{fig:openmap-wm-bad}
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\end{figure}
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\section{Conclusions}
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\label{sec:conclusions}
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2
vars.awk
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vars.awk
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@ -10,7 +10,7 @@ BEGIN { FS="[(); ]" }
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x2 += 1;
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d2 = sprintf("\\newcommand{\\isolationThreshold}{%.1f}",$7);
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}
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/scale constant float default / {
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/scale2 constant float default / {
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x3 += 1;
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d3 = sprintf("\\newcommand{\\exaggerationEnthusiasm}{%.1f}",$7);
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}
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62
wm.sql
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wm.sql
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@ -417,7 +417,9 @@ begin
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return st_split(st_snap(input, blade, 0.00000001), blade);
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end $$ language plpgsql;
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-- wm_exaggerate_bend2 is the second version of bend exaggeration. Uses
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-- non-linear interpolation by point azimuth. Slower, but produces nicer
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-- exaggerated geometries.
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drop function if exists wm_exaggerate_bend2;
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create function wm_exaggerate_bend2(
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INOUT bend geometry,
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@ -425,7 +427,7 @@ create function wm_exaggerate_bend2(
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desired_size float
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) as $$
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declare
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scale constant float default 1.2; -- exaggeration enthusiasm
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scale2 constant float default 1.2; -- exaggeration enthusiasm
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midpoint geometry; -- midpoint of the baseline
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points geometry[];
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startazimuth float;
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@ -459,7 +461,7 @@ begin
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if diffazimuth > 90 then
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diffazimuth = 180 - diffazimuth;
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end if;
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sss = ((scale-1) * (diffazimuth / 90)^0.5);
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sss = ((scale2-1) * (diffazimuth / 90)^0.5);
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point = st_transform(
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st_project(
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st_transform(point, 4326)::geography,
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@ -472,6 +474,60 @@ begin
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end loop;
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end $$ language plpgsql;
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-- wm_exaggerate_bend exaggerates a given bend. Uses naive linear
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-- interpolation. Faster than wm_exaggerate_bend2, but result visually looks
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-- worse.
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drop function if exists wm_exaggerate_bend;
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create function wm_exaggerate_bend(
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INOUT bend geometry,
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size float,
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desired_size float
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) as $$
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declare
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scale constant float default 1.2; -- exaggeration enthusiasm
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midpoint geometry; -- midpoint of the baseline
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splitbend geometry; -- bend split across its half
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bendm geometry; -- bend with coefficients to prolong the lines
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points geometry[];
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begin
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if size = 0 then
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raise 'invalid input: zero-area bend';
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end if;
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midpoint = st_lineinterpolatepoint(st_makeline(
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st_pointn(bend, 1),
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st_pointn(bend, -1)
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), .5);
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while size < desired_size loop
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splitbend = wm_st_split(bend, st_lineinterpolatepoint(bend, .5));
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-- Convert bend to LINESTRINGM, where M is the fraction by how
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-- much the point will be prolonged:
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-- 1. draw a line between midpoint and the point on the bend.
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-- 2. multiply the line length by M. Midpoint stays intact.
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-- 3. the new set of lines form a new bend.
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-- Uses linear interpolation; can be updated to gaussian or similar;
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-- then interpolate manually instead of relying on st_addmeasure.
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bendm = st_collect(
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st_addmeasure(st_geometryn(splitbend, 1), 1, scale),
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st_addmeasure(st_geometryn(splitbend, 2), scale, 1)
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);
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points = array((
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select st_scale(
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st_makepoint(st_x(geom), st_y(geom)),
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st_makepoint(st_m(geom), st_m(geom)),
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midpoint
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)
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from st_dumppoints(bendm)
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order by path[1], path[2]
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));
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bend = st_setsrid(st_makeline(points), st_srid(bend));
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size = wm_adjsize(bend);
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end loop;
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end $$ language plpgsql;
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-- wm_adjsize calculates adjusted size for a polygon. Can return 0.
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drop function if exists wm_adjsize;
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create function wm_adjsize(bend geometry, OUT adjsize float) as $$
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