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<H1><A NAME="SECTION0015120000000000000000"></A>
<A NAME="sec:example_12"></A><A NAME="24442"></A>
<BR>
7.12 Optimal triangulation of data
</H1>
<P>
Our next example (Figure <A HREF="#fig:GMT_example_12">7.12</A>)
operates on a data set of topographic
readings non-uniformly distributed in the plane (Table
5.11 in Davis: <I>Statistics and Data Analysis in Geology</I>,
J. Wiley). We use <A NAME="tex2html1382"
HREF="../man/triangulate.html"><I><B>triangulate</B></I></A><A NAME="25110"></A> to perform the optimal
Delaunay triangulation, then use the output to draw the
resulting network. We label the node numbers as well as
the node values, and call <A NAME="tex2html1383"
HREF="../man/pscontour.html"><I><B>pscontour</B></I></A><A NAME="25115"></A> to make a contour
map and image directly from the raw data. Thus, in this
example we do not actually make grid files but still
are able to contour and image the data. We use a color
palette table <U>topo.cpt</U> (created via <A NAME="tex2html1384"
HREF="../man/minmax.html"><I><B>minmax</B></I></A><A NAME="25121"></A> and <A NAME="tex2html1385"
HREF="../man/makecpt.html"><I><B>makecpt</B></I></A><A NAME="25126"></A>).
The script becomes:
<P>
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<PRE>#!/bin/sh
# GMT EXAMPLE 12
#
# Purpose: Illustrates Delaunay triangulation of points, and contouring
# GMT progs: makecpt, minmax, pscontour, pstext, psxy, triangulate
# Unix progs: $AWK, echo, rm
#
# First draw network and label the nodes
#
ps=example_12.ps
triangulate table_5.11 -m > net.xy
psxy -R0/6.5/-0.2/6.5 -JX3.06i/3.15i -B2f1WSNe -m net.xy -Wthinner -P -K -X0.9i -Y4.65i > $ps
psxy table_5.11 -R -J -O -K -Sc0.12i -Gwhite -Wthinnest >> $ps
$AWK '{print $1, $2, 6, 0, 0, "CM", NR-1}' table_5.11 | pstext -R -J -O -K >> $ps
#
# Then draw network and print the node values
#
psxy -R -J -B2f1eSNw -m net.xy -Wthinner -O -K -X3.25i >> $ps
psxy -R -J -O -K table_5.11 -Sc0.03i -Gblack >> $ps
$AWK '{printf "%g %s 6 0 0 LM %g\n", $1, $2, $3}' table_5.11 | pstext -R -J -O -K -Wwhite,o \
-C0.01i/0.01i -D0.08i/0i -N >> $ps
#
# Then contour the data and draw triangles using dashed pen; use "minmax" and "makecpt" to make a
# color palette (.cpt) file
#
T=`minmax -T25/2 table_5.11`
makecpt -Cjet $T > topo.cpt
pscontour -R -J table_5.11 -B2f1WSne -Wthin -Ctopo.cpt -Lthinnest,- -G1i/0 -X-3.25i -Y-3.65i -O -K \
-U"Example 12 in Cookbook" >> $ps
#
# Finally color the topography
#
pscontour -R -J table_5.11 -B2f1eSnw -Ctopo.cpt -I -X3.25i -O -K >> $ps
echo "3.16 8 30 0 1 BC Delaunay Triangulation" | \
pstext -R0/8/0/11 -Jx1i -O -X-3.25i >> $ps
#
rm -f net.xy topo.cpt .gmt*
</PRE>
<BR CLEAR="ALL">
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<DIV ALIGN="CENTER"><A NAME="fig:GMT_example_12"></A><A NAME="25132"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 7.12:</STRONG>
Optimal triangulation of data.</CAPTION>
<TR><TD>
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Paul Wessel
2010-07-14
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