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<H1><A NAME="SECTION0014150000000000000000"></A>
<A NAME="11439"></A>
<BR>
6.15 Gridding, contouring, and masking of unconstrained areas
</H1>
<P>
This example (Figure <A HREF="node88.html#fig:GMT_example_15">6.15</A>) demonstrates
some off the different ways one
can use to grid data in <A NAME="tex2html431"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A>, and how to deal with unconstrained
areas. We first convert a large ASCII file to binary with
<A NAME="tex2html432"
HREF="../gmtconvert.html"><I><B>gmtconvert</B></I></A><A NAME="11459"></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="tex2html433"
HREF="../nearneighbor.html"><I><B>nearneighbor</B></I></A><A NAME="11468"></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="tex2html434"
HREF="../surface.html"><I><B>surface</B></I></A><A NAME="11477"></A>) which is a global method. Hence, the contours
cover the entire map allthough the data are only available for
portions of the area (indicated by the gray areas plotted using
<A NAME="tex2html435"
HREF="../psmask.html"><I><B>psmask</B></I></A><A NAME="11486"></A>). The top left scenario illustrates how we can
create a clip path (using <A NAME="tex2html436"
HREF="../psmask.html"><I><B>psmask</B></I></A><A NAME="11495"></A>) based on the data coverage
to eliminate contours outside the constrained area.
Finally (top right) we simply employ <A NAME="tex2html437"
HREF="../pscoast.html"><I><B>pscoast</B></I></A><A NAME="11504"></A> to overlay
gray landmasses to cover up the unwanted contours, and end by
plotting a star at the deepest point on the map with <A NAME="tex2html438"
HREF="../psxy.html"><I><B>psxy</B></I></A><A NAME="11513"></A>.
This point was extracted from the gridded files using <A NAME="tex2html439"
HREF="../grdinfo.html"><I><B>grdinfo</B></I></A><A NAME="11522"></A>.
<P>
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<P>
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<HR>
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<PRE>
gmtconvert ship.xyz -bo >! ship.b
set region = `minmax ship.b -I1 -bi3`
nearneighbor $region -I10m -S40k -Gship.grd ship.b -bi3
set info = `grdinfo -C -M ship.grd`
grdcontour ship.grd -JM3i -P -B2WSne -C250 -A1000 -G2i -K -U"Example 15 in Cookbook" >! example_15.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 -JM -O -K -T -G220 -bi3 -X3.6i >> example_15.ps
grdcontour ship.grd -JM -B2WSne -C250 -L-8000/0 -A1000 -G2i -O -K >> example_15.ps
psmask $region -I10m ship_10m.b -bi3 -JM -B2WSne -O -K -X-3.6i -Y3.75i >> example_15.ps
grdcontour ship.grd -JM -C250 -A1000 -L-8000/0 -G2i -O -K >> example_15.ps
psmask -C -O -K >> example_15.ps
grdclip ship.grd -Sa-1/NaN -Gship_clipped.grd
grdcontour ship_clipped.grd -JM -B2WSne -C250 -A1000 -L-8000/0 -G2i -O -K -X3.6i >> example_15.ps
pscoast $region -JM -O -K -G150 -W0.25p >> example_15.ps
echo $info[12] $info[13] | psxy -R -JM -O -K -Sa0.15i -W1p >> example_15.ps
echo "-0.3 3.6 24 0 1 CB Gridding with missing data" | pstext -R0/3/0/4 -Jx1i -O -N >> example_15.ps
\rm -f ship.b ship_10m.b ship.grd ship_clipped.grd
</PRE>
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<DIV ALIGN="CENTER"><A NAME="fig:GMT_example_15"></A><A NAME="11592"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 6.15:</STRONG>
Gridding, contouring, and masking of data</CAPTION>
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WIDTH="407" HEIGHT="453" BORDER="0"
SRC="img118.gif"
ALT="\begin{figure}\centering\epsfig{figure=eps/GMT_example_15.eps}\end{figure}"></TD></TR>
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<ADDRESS>
Paul Wessel
2001-04-18
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