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<H2><A NAME="SECTION001347000000000000000">
5.4.7 General Cylindrical Projections (<B>-Jy</B> <B>-JY</B>)</A>
</H2>
<P>
<A NAME="8555"></A>
<A NAME="8556"></A>
<A NAME="8557"></A>
<P>
This cylindrical projection is actually several projections,
depending on what latitude is selected as the standard parallel.
However, they are all equal area and hence non-conformal. All
meridians and parallels are straight lines. The requirements
to define this projection are:
<P>
<DL>
<DD><P>
</DD>
<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>The standard parallel
<P>
</DD>
<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>Scale in inch/degree or as 1:xxxxx (<B>-Jy</B>),
or map width (<B>-JY</B>)
<P>
</DD>
</DL>
<P>
While you may choose any value for the standard parallel and
obtain your own personal projection, there are four choices of
standard parallels that result in known (or named) projections.
These are listed in Table <A HREF="node63.html#tbl:stdparr">5.1</A>.
<P>
<BR><P></P>
<DIV ALIGN="CENTER"><A NAME="8543"></A>
<TABLE>
<CAPTION><STRONG>Table 5.1:</STRONG>
Standard parallels for some cylindrical projections</CAPTION>
<TR><TD>
<DIV ALIGN="CENTER"><TABLE CELLPADDING=3 BORDER="1">
<TR><TD ALIGN="CENTER" COLSPAN=1><I>Projection name</I></TD>
<TD ALIGN="CENTER" COLSPAN=1><I>Standard parallel</I></TD>
</TR>
<TR><TD ALIGN="LEFT">Lambert</TD>
<TD ALIGN="CENTER">0<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$"></TD>
</TR>
<TR><TD ALIGN="LEFT">Behrman</TD>
<TD ALIGN="CENTER">30<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$"></TD>
</TR>
<TR><TD ALIGN="LEFT">Trystan-Edwards</TD>
<TD ALIGN="CENTER">37<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">24' (= 37.4<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">)</TD>
</TR>
<TR><TD ALIGN="LEFT">Peters (Gall)</TD>
<TD ALIGN="CENTER">45<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$"></TD>
</TR>
</TABLE>
<A NAME="tbl:stdparr"></A></DIV></TD></TR>
</TABLE>
</DIV><P></P>
<BR>
<P>
For instance, a world map centered on the 35<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">E meridian
using the Behrman projection can be obtained by running the command:
<A NAME="8546"></A>
<A NAME="8547"></A>
<A NAME="8548"></A>
<A NAME="8549"></A>
<A NAME="8550"></A>
<P>
<P>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<BR>
<PRE>
#!/bin/sh
# $Id: GMT_general_cyl.sh,v 1.1 2001/03/21 04:10:21 pwessel Exp $
#
pscoast -R-145/215/-90/90 -JY35/30/4.5i -B45g45 -Dc -A10000 -S200 -W0.25p -P > GMT_general_cyl.ps
</PRE>
<P>
<BR>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<P></P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_general_cyl"></A><A NAME="8720"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5.24:</STRONG>
World map using the Behrman cylindrical projection</CAPTION>
<TR><TD><IMG
WIDTH="530" HEIGHT="277" BORDER="0"
SRC="img86.gif"
ALT="\begin{figure}\centering\epsfig{figure=eps/GMT_general_cyl.eps}\end{figure}"></TD></TR>
</TABLE>
</DIV><P></P>
<P>
As one can see there is considerable distortion at high latitudes
since the poles map into lines.
<P>
<A NAME="8711"></A>
<A NAME="8712"></A>
<A NAME="8713"></A>
<P>
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<ADDRESS>
Paul Wessel
2001-04-18
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