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<H1><A NAME="SECTION0014200000000000000000"></A>
<A NAME="12095"></A>
<BR>
6.20 Custom map symbols
</H1>
<P>
One is often required to make special maps that shows the
distribution of certain features but one would prefer to
use a custom symbol instead of the built-in circles,
squares, triangles, etc. in the <A NAME="tex2html483"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> plotting programs
<A NAME="tex2html484"
HREF="../psxy.html"><I><B>psxy</B></I></A><A NAME="12136"></A> and <A NAME="tex2html485"
HREF="../psxyz.html"><I><B>psxyz</B></I></A><A NAME="12145"></A>. Here we demonstrate one
approach that allows for a fair bit of flexibility in
designing ones own symbols. The following recipe is used
when designing a new symbol. (1) Use <A NAME="tex2html486"
HREF="../psbasemap.html"><I><B>psbasemap</B></I></A><A NAME="12154"></A> (or
engineering paper!) to set up an empty grid that goes from
-0.5 to +0.5 in both <I>x</I> and <I>y</I>. Use ruler and
compass to draw your new symbol using straight lines and
arcs of circles. This is how your symbol will look when
a size of 1 inch is chosen. Figure <A HREF="node93.html#fig:GMT_volcano">6.20</A> illustrates a
new symbol we will call volcano.
<P>
<P></P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_volcano"></A><A NAME="12163"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 6.20:</STRONG>
Making a new volcano symbol for <A NAME="tex2html477"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A></CAPTION>
<TR><TD><IMG
WIDTH="299" HEIGHT="268" BORDER="0"
SRC="img126.gif"
ALT="\begin{figure}\centering\epsfig{figure=eps/GMT_volcano.eps}\end{figure}"></TD></TR>
</TABLE>
</DIV><P></P>
<P>
(2) After designing the symbol we will encode it using a
simple set of rules. In our case we describe our volcano
using no more than 4 possible constructs:
<P>
<PRE><TT>
<P>
<P>
<IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img127.gif"
ALT="$x_0$"> <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img128.gif"
ALT="$y_0$"> <B>M</B> [ <B>-G</B><I>fill</I> ] [ <B>-W</B><I>pen</I> ] Startnew element at <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img127.gif"
ALT="$x_0$">, <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img128.gif"
ALT="$y_0$">
<BR><P>
<IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img129.gif"
ALT="$x_1$"> <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img130.gif"
ALT="$y_1$"> <B>D</B> Draw straight line from current point to <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img129.gif"
ALT="$x_1$">, <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img130.gif"
ALT="$y_1$">
<BR><P>
<IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img127.gif"
ALT="$x_0$"> <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img128.gif"
ALT="$y_0$"> <IMG
WIDTH="11" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img131.gif"
ALT="$r$"> <IMG
WIDTH="24" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img132.gif"
ALT="$\Delta\alpha$"> <B>C</B> [ <B>-G</B><I>fill</I> ] [ <B>-W</B><I>pen</I> ] Drawsingle circle of radius <IMG
WIDTH="11" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img131.gif"
ALT="$r$"> around <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img127.gif"
ALT="$x_0$">, <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img128.gif"
ALT="$y_0$"> in steps of <IMG
WIDTH="24" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img132.gif"
ALT="$\Delta\alpha$"><IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">
<BR><P>
<IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img127.gif"
ALT="$x_0$"> <IMG
WIDTH="18" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img128.gif"
ALT="$y_0$"> <IMG
WIDTH="11" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img131.gif"
ALT="$r$"> <IMG
WIDTH="21" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img133.gif"
ALT="$\alpha_1$"> <IMG
WIDTH="21" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img134.gif"
ALT="$\alpha_2$"> <IMG
WIDTH="24" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img132.gif"
ALT="$\Delta\alpha$"> <B>A</B> Drawarc segment of radius <IMG
WIDTH="11" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img131.gif"
ALT="$r$"> from angle <IMG
WIDTH="21" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img133.gif"
ALT="$\alpha_1$"> to <IMG
WIDTH="21" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img134.gif"
ALT="$\alpha_2$">every <IMG
WIDTH="24" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img132.gif"
ALT="$\Delta\alpha$"><IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">
<P>
</TT></PRE>
<P>
The optional <B>-G</B> and <B>-W</B> can be used to hardwire
the color fill and pen for segments. By default the segments
are painted based on the values of the command line settings.
<P>
Manually applying these rules to our symbol results in a
definition file <U>volcano.def</U>:
<P>
<P>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<BR>
<PRE>
-0.5 -0.5 M
-0.2 0 D
-0.1 0.173205081 0.2 240 300 2 A
0 0 D
0.3 -0.5 D
-0.05 0.15 0.1 5 C
0.15 0.3 0.075 5 C
0.325 0.4 0.05 10 C
0.45 0.45 0.025 10 C
</PRE>
<P>
<BR>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<P>
The values refer to positions and dimensions illustrated
in Figure <A HREF="node93.html#fig:GMT_volcano">6.20</A> above. (3) Given a proper
definition file we use the supplied <I>$AWK</I><A NAME="12359"></A>-script <U>make_symbol</U>
to create a custom <I>$AWK</I><A NAME="12365"></A>-script that will read locations and
sizes of the desired symbols and replace them with line-drawings
like the one in the figure but translated and scaled accordingly.
The output is a multi-segment file (see Appendix B) which may
be plotted with <A NAME="tex2html487"
HREF="../psxy.html"><I><B>psxy</B></I></A><A NAME="12371"></A> or <A NAME="tex2html488"
HREF="../psxyz.html"><I><B>psxyz</B></I></A><A NAME="12380"></A>.
<P>
We are now ready to give it a try. Based on the hotspot
locations in the file <U>hotspots.d</U> (with a 3rd column
giving the desired symbol sizes in inches) we lay down a
world map and overlay red volcano symbols using our custom-built
<I>$AWK</I><A NAME="12389"></A>-script <U>volcano.awk</U> and <A NAME="tex2html489"
HREF="../psxy.html"><I><B>psxy</B></I></A><A NAME="12396"></A>.
Note that you must first transform the coordinates using
<A NAME="tex2html490"
HREF="../mapproject.html"><I><B>mapproject</B></I></A><A NAME="12405"></A> prior to running the <I>$AWK</I><A NAME="12413"></A>-script.
Without further discussion we also make a definition for a multi-
colored bulls-eye symbol:
<P>
<P>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<BR>
<PRE>
0 -0.7 M -W0.5p/255/0/0p
0 0.7 D
-0.7 0 M -W0.5p/255/0/0p
0.7 0 D
0 0 0.45 5 C -Gp0/12
0 0 0.45 5 C -W0.25p
0 0 0.35 5 C -G255/255/0 -W0.25p
0 0 0.25 5 C -Gp0/9
0 0 0.25 5 C -W0.25p
0 0 0.15 5 C -G255/255/0 -W0.25p
0 0 0.05 5 C -G255 -W0.25p
</PRE>
<P>
<BR>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<P>
Here is our final map script:
<P>
<P>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<BR>
<PRE>
$AWK -f make_symbol < volcano.def >! volcano.awk
$AWK -f make_symbol < bullseye.def >! bullseye.awk
cat << EOF >! hotspots.d
55.5 -21.0 0.25
63.0 -49.0 0.25
-12.0 -37.0 0.25
-28.5 29.34 0.25
48.4 -53.4 0.25
155.5 -40.4 0.25
-155.5 19.6 0.5
-138.1 -50.9 0.25
-153.5 -21.0 0.25
-116.7 -26.3 0.25
-16.5 64.4 0.25
EOF
pscoast -R0/360/-90/90 -JR180/9i -B60/30:."Hotspot Islands and Cities": -G0/150/0 -S200/200/255 \
-Dc -A5000 -K -U"Example 20 in Cookbook" >! example_20.ps
mapproject -R0/360/-90/90 -JR -Di hotspots.d | $AWK -f volcano.awk | psxy -R0/9/0/9 -Jx1i -O -K \
-M -W0.25p -G255/0/0 -L >> example_20.ps
cat << EOF >! cities.d
286 40.45 0.8
31.15 30.03 0.8
115.49 -31.58 0.8
EOF
mapproject -R0/360/-90/90 -JR -Di cities.d | $AWK -f bullseye.awk | psxy -R0/9/0/9 -Jx -O \
-M >> example_20.ps
\rm -f volcano.awk bullseye.awk hotspots.d cities.d
</PRE>
<P>
<BR>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<P>
which produces the plot in Figure <A HREF="node93.html#fig:GMT_example_20">6.21</A>.
<P>
<P></P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_example_20"></A><A NAME="12470"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 6.21:</STRONG>
Using custom symbols in <A NAME="tex2html480"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A></CAPTION>
<TR><TD><IMG
WIDTH="554" HEIGHT="410" BORDER="0"
SRC="img135.gif"
ALT="\begin{figure}\centering\epsfig{figure=eps/GMT_example_20.eps}\end{figure}"></TD></TR>
</TABLE>
</DIV><P></P>
<P>
Given these guidelines you can easily make your own symbols.
Symbols with more than one color can be obtained by making
several symbol components. E.g., to have yellow smoke coming
out of red volcanoes we would make two symbols: one with just
the cone and caldera and the other with the bubbles. These
would be plotted consecutively using the desired colors.
Alternatively, like in <U>bullseye.def</U>, we may
specify colors directly for the various segments. Note that
the custom symbols, unlike the built-in symbols in <A NAME="tex2html491"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A>, can
be used with the built-in patterns (Appendix E). Other
approaches are also possible, of course.
<A NAME="12467"></A>
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<ADDRESS>
Paul Wessel
2001-04-18
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