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<H2><A NAME="SECTION001355000000000000000">
5.5.5 Eckert IV and VI Projection (<B>-Jk</B> <B>-JK</B>)</A>
</H2>
<P>
<A NAME="9352"></A>
<A NAME="9353"></A>
<A NAME="9354"></A>
<P>
The Eckert IV and VI projections, presented by Max Eckert in 1906,
are pseudocylindrical equal-area projections. Central meridian
and all parallels are straight lines; other meridians are
equally spaced elliptical arcs (IV) or sinusoids (VI). The scale is
true along latitudes <IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img53.gif"
ALT="$\pm$"> 40<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">30' (IV) and <IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img53.gif"
ALT="$\pm$"> 49<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">16' (VI).
Their main use is in thematic world maps. To select Eckert IV you must
use <B>-JKf</B> (<B>f</B> for ``four'') while Eckert VI is selected with
<B>-JKs</B> (<B>s</B> for ``six''). If no modifier is given it defaults to
Eckert VI.
In addition, you must enter
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<DD><P>
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<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>The central meridian
<P>
</DD>
<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>Scale along equator in inch/degree or
1:xxxxx (<B>-Jk</B>), or map width (<B>-JK</B>)
<P>
</DD>
</DL>
<P>
Centered on the Dateline, the Eckert IV example below was created by this command:
<P>
<P>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<BR>
<PRE>
#!/bin/sh
# $Id: GMT_eckert4.sh,v 1.1 2001/03/21 04:10:21 pwessel Exp $
#
pscoast -R0/360/-90/90 -JKf180/4.5i -Bg30/g15 -Dc -A10000 -W0.25p -G255 -S200 -P > GMT_eckert4.ps
</PRE>
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<P></P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_eckert4"></A><A NAME="9503"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5.30:</STRONG>
World map using the Eckert IV projection</CAPTION>
<TR><TD><IMG
WIDTH="520" HEIGHT="261" BORDER="0"
SRC="img92.gif"
ALT="\begin{figure}\centering\epsfig{figure=eps/GMT_eckert4.eps}\end{figure}"></TD></TR>
</TABLE>
</DIV><P></P>
<P>
The same script, with <B>s</B> instead of <B>f</B>, yields the Eckert VI map:
<P>
<P></P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_eckert6"></A><A NAME="9508"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5.31:</STRONG>
World map using the Eckert VI projection</CAPTION>
<TR><TD><IMG
WIDTH="520" HEIGHT="261" BORDER="0"
SRC="img93.gif"
ALT="\begin{figure}\centering\epsfig{figure=eps/GMT_eckert6.eps}\end{figure}"></TD></TR>
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<ADDRESS>
Paul Wessel
2001-04-18
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