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<H1><A NAME="SECTION0015150000000000000000"></A>
<A NAME="sec:example_15"></A><A NAME="23898"></A>
<BR>
7.15 Gridding, contouring, and masking of unconstrained areas
</H1>
<P>
This example (Figure <A HREF="#fig:GMT_example_15">7.15</A>) demonstrates
some off the different ways one
can use to grid data in <A NAME="tex2html1375"
HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A>, and how to deal with unconstrained
areas. We first convert a large ASCII file to binary with
<A NAME="tex2html1376"
HREF="../man/gmtconvert.html"><I><B>gmtconvert</B></I></A><A NAME="24634"></A> since the binary file will read and process
much faster. Our lower left plot illustrates the results of
gridding using a nearest neighbor technique (<A NAME="tex2html1377"
HREF="../man/nearneighbor.html"><I><B>nearneighbor</B></I></A><A NAME="24639"></A>)
which is a local method: No output is given where there are no data.
Next (lower right), we use a minimum curvature technique
(<A NAME="tex2html1378"
HREF="../man/surface.html"><I><B>surface</B></I></A><A NAME="24644"></A>) which is a global method. Hence, the contours
cover the entire map although the data are only available for
portions of the area (indicated by the gray areas plotted using
<A NAME="tex2html1379"
HREF="../man/psmask.html"><I><B>psmask</B></I></A><A NAME="24649"></A>). The top left scenario illustrates how we can
create a clip path (using <A NAME="tex2html1380"
HREF="../man/psmask.html"><I><B>psmask</B></I></A><A NAME="24654"></A>) based on the data coverage
to eliminate contours outside the constrained area.
Finally (top right) we simply employ <A NAME="tex2html1381"
HREF="../man/pscoast.html"><I><B>pscoast</B></I></A><A NAME="24659"></A> to overlay
gray land masses to cover up the unwanted contours, and end by
plotting a star at the deepest point on the map with <A NAME="tex2html1382"
HREF="../man/psxy.html"><I><B>psxy</B></I></A><A NAME="24664"></A>.
This point was extracted from the grid files using <A NAME="tex2html1383"
HREF="../man/grdinfo.html"><I><B>grdinfo</B></I></A><A NAME="24669"></A>.
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<PRE>#!/bin/sh
# GMT EXAMPLE 15
#
# Purpose: Gridding and clipping when data are missing
# GMT progs: blockmedian, gmtconvert, grdclip, grdcontour, grdinfo, minmax
# GMT progs: nearneighbor, pscoast, psmask, pstext, surface
# Unix progs: awk, echo, rm
#
ps=example_15.ps
gmtconvert ship.xyz -bo > ship.b
#
region=`minmax ship.b -I1 -bi3`
nearneighbor $region -I10m -S40k -Gship.grd ship.b -bi3
info=`grdinfo -C -M ship.grd`
grdcontour ship.grd -JM3i -P -B2WSne -C250 -A1000 -G2i -K -U"Example 15 in Cookbook" > $ps
#
blockmedian $region -I10m ship.b -bi3 -bo > ship_10m.b
surface $region -I10m ship_10m.b -Gship.grd -bi3
psmask $region -I10m ship.b -J -O -K -T -Glightgray -bi3 -X3.6i >> $ps
grdcontour ship.grd -J -B2WSne -C250 -L-8000/0 -A1000 -G2i -O -K >> $ps
#
psmask $region -I10m ship_10m.b -bi3 -J -B2WSne -O -K -X-3.6i -Y3.75i >> $ps
grdcontour ship.grd -J -C250 -A1000 -L-8000/0 -G2i -O -K >> $ps
psmask -C -O -K >> $ps
#
grdclip ship.grd -Sa-1/NaN -Gship_clipped.grd
grdcontour ship_clipped.grd -J -B2WSne -C250 -A1000 -L-8000/0 -G2i -O -K -X3.6i >> $ps
pscoast $region -J -O -K -Ggray -Wthinnest >> $ps
echo $info | awk '{print $12,$13}' | psxy -R -J -O -K -Sa0.15i -Wthick >> $ps
echo "-0.3 3.6 24 0 1 CB Gridding with missing data" | pstext -R0/3/0/4 -Jx1i -O -N >> $ps
rm -f ship.b ship_10m.b ship.grd ship_clipped.grd .gmt*
</PRE>
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<DIV ALIGN="CENTER"><A NAME="fig:GMT_example_15"></A><A NAME="24675"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 7.15:</STRONG>
Gridding, contouring, and masking of data.</CAPTION>
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2010-01-14
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