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<H2><A NAME="SECTION001242000000000000000">
4.4.2 Coordinate transformations and map projections: The <B>-J</B> option</A>
</H2>
<A NAME="18064"></A>
<A NAME="16920"></A>
<P>
This option selects the coordinate transformation or map projection. The general format is
<UL>
<LI><B>-J</B><IMG
WIDTH="14" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img43.png"
ALT="$\delta$">[<I>parameters</I>/]<I>scale</I>. Here, <IMG
WIDTH="14" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img43.png"
ALT="$\delta$"> is a <I>lower-case</I>
letter of the alphabet that selects a particular map projection, the <I>parameters</I>
is zero or more slash-delimited projection parameter, and <I>scale</I> is map scale given in
distance units per degree or as 1:xxxxx.
</LI>
<LI><B>-J</B><IMG
WIDTH="14" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img44.png"
ALT="$\Delta$">[<I>parameters</I>/]<I>width</I>. Here, <IMG
WIDTH="14" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img44.png"
ALT="$\Delta$"> is an <I>upper-case</I>
letter of the alphabet that selects a particular map projection, the <I>parameters</I>
is zero or more slash-delimited projection parameter, and <I>width</I> is map width (map
height is automatically computed from the implied map scale and region).
</LI>
</UL>
Since <A NAME="tex2html1078"
HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> version 4.3.0, there is an alternative way to specify the projections: use the same abbreviation as in the mapping package <I>Proj4</I><A NAME="18355"></A>. The options thus either look like:
<UL>
<LI><B>-Jabbrev/</B>[<I>parameters</I>/]<I>scale</I>. Here, <B>abbrev</B> is a <I>lower-case</I>
abbreviation that selects a particular map projection, the <I>parameters</I>
is zero or more slash-delimited projection parameter, and <I>scale</I> is map scale given in
distance units per degree or as 1:xxxxx.
</LI>
<LI><B>-JAbbrev/</B>[<I>parameters</I>/]<I>width</I>. Here, <B>Abbrev</B> is an <I>capitalized</I> abbreviation that selects a particular map projection, the <I>parameters</I>
is zero or more slash-delimited projection parameter, and <I>width</I> is map width (map
height is automatically computed from the implied map scale and region).
</LI>
</UL>
<P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_-J"></A><A NAME="18361"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure:</STRONG>
The 30+ map projections and coordinate transformations available in <A NAME="tex2html1075"
HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A>.</CAPTION>
<TR><TD>
<DIV ALIGN="CENTER"><IMG
WIDTH="526" HEIGHT="326" ALIGN="BOTTOM" BORDER="0"
SRC="img45.png"
ALT="\includegraphics{scripts/GMT_-J}"></DIV></TD></TR>
</TABLE>
</DIV>
<P>
The projections available in <A NAME="tex2html1079"
HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> are presented in Figure <A HREF="#fig:GMT_-J">4.5</A>.
For details on all <A NAME="tex2html1080"
HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> projections and the required parameters, see the <A NAME="tex2html1081"
HREF="../man/psbasemap.html"><I><B>psbasemap</B></I></A><A NAME="18375"></A> man page.
We will also show examples of every projection in the next Chapters, and a quick
summary of projection syntax was given in Chapter <A HREF="node27.html#ch:3">3</A>.
<P>
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<ADDRESS>
Paul Wessel
2010-01-14
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