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5.1.2 Cartesian logarithmic projection
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<DIV ALIGN="CENTER"><A NAME="fig:GMT_log"></A><A NAME="20606"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5.4:</STRONG>
Logarithmic transformation of <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img4.png"
ALT="$x$">-coordinates.</CAPTION>
<TR><TD>
<DIV ALIGN="CENTER"><IMG
WIDTH="391" HEIGHT="209" ALIGN="BOTTOM" BORDER="0"
SRC="img98.png"
ALT="\includegraphics{scripts/GMT_log}"></DIV></TD></TR>
</TABLE>
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<P>
The log<IMG
WIDTH="17" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$_{10}$"> transformation is simply <!-- MATH
$u' = a \log_{10}(u) + b$
-->
<IMG
WIDTH="123" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
SRC="img99.png"
ALT="$u' = a \log_{10}(u) + b$"> and is selected by appending an <B>l</B>
(lower case L) immediately following the scale (or axis length)
value. Hence, to produce a plot in which the <I>x</I>-axis is
logarithmic (the <I>y</I>-axis remains linear, i.e., a semi-log plot), try
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<PRE>psxy -R1/100/0/10 -Jx1.5il/0.15i -B2g3/a2f1g2WSne -Wthick,- -P -K -H sqrt.d > GMT_log.ps
psxy -R -J -Ss0.075i -Gblack -W -O -H sqrt.d10 >> GMT_log.ps
</PRE>
<BR CLEAR="ALL">
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<P>
Note that if <I>x</I>- and <I>y</I>-scaling are different and
a log<IMG
WIDTH="17" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$_{10}$">-log<IMG
WIDTH="17" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$_{10}$"> plot is desired, the <B>l</B> must be
appended twice: Once after the <I>x</I>-scale (before the /) and
once after the <I>y</I>-scale.
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<ADDRESS>
Paul Wessel
2010-01-14
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