<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 2002-2-1 (1.71) original version by: Nikos Drakos, CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>6. GMT Map Projections</TITLE> <META NAME="description" CONTENT="6. 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They all project the input coordinates longitude and latitude to positions on a map. In general, <IMG WIDTH="88" HEIGHT="32" ALIGN="MIDDLE" BORDER="0" SRC="img119.png" ALT="$x' = f(x,y,z)$"> and <IMG WIDTH="87" HEIGHT="32" ALIGN="MIDDLE" BORDER="0" SRC="img120.png" ALT="$y' = g(x,y,z)$">, where <IMG WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" SRC="img20.png" ALT="$z$"> is implicitly given as the radial vector length to the <IMG WIDTH="37" HEIGHT="31" ALIGN="MIDDLE" BORDER="0" SRC="img85.png" ALT="$(x,y)$"> point on the chosen ellipsoid. The functions <IMG WIDTH="13" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" SRC="img92.png" ALT="$f$"> and <IMG WIDTH="12" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" SRC="img121.png" ALT="$g$"> can be quite nasty and we will refrain from presenting details in this document. The interested read is referred to <I>Snyder</I> [1987]<A NAME="tex2html1261" HREF="footnode.html#foot21660"><SUP>6.1</SUP></A>. We will mostly be using the <A NAME="tex2html1263" HREF="../man/pscoast.html"><I><B>pscoast</B></I></A><A NAME="22613"></A> command to demonstrate each of the projections. <A NAME="tex2html1264" HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> map projections are grouped into four categories depending on the nature of the projection. The groups are <P> <OL> <LI>Conic map projections </LI> <LI>Azimuthal map projections </LI> <LI>Cylindrical map projections </LI> <LI>Miscellaneous projections </LI> </OL> <P> Because <IMG WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" SRC="img4.png" ALT="$x$"> and <IMG WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" SRC="img30.png" ALT="$y$"> are coupled we can only specify one plot-dimensional scale, typically a map <I>scale</I> (for lower-case map projection code) or a map <I>width</I> (for upper-case map projection code). However, in some cases it would be more practical to specify map <I>height</I> instead of <I>width</I>, while in other situations it would be nice to set either the <I>shortest</I> or <I>longest</I> map dimension. Users may select these alternatives by appending a character code to their map dimension. To specify map <I>height</I>, append <B>h</B> to the given dimension; to select the minimum map dimension, append <B>-</B>, whereas you may append <B>+</B> to select the maximum map dimension. Without the modifier the map width is selected by default. <P> In <A NAME="tex2html1265" HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> version 4.3.0 we noticed we ran out of the alphabet for 1-letter (and sometimes 2-letter) projection codes. To allow more flexibility, and to make it easier to remember the codes, we implemented the option to use the abbreviations used by the <I>Proj4</I><A NAME="22623"></A> mapping package. Since some of the <A NAME="tex2html1266" HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> projections are not in <I>Proj4</I><A NAME="22629"></A>, we invented some of our own as well. For a full list of both the old 1- and 2-letter codes, as well as the <I>Proj4</I><A NAME="22632"></A>-equivalents see the quick reference cards in Section <A HREF="node30.html#sec:purpose">3.2</A>. For example, <B>-JM15c</B> and <B>-JMerc/15c</B> have the same meaning. <P> <BR><HR> <!--Table of Child-Links--> <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A> <UL> <LI><A NAME="tex2html3761" HREF="node86.html">6.1 Conic projections</A> <UL> <LI><A NAME="tex2html3762" HREF="node87.html">6.1.1 Albers conic equal-area projection (<B>-Jb</B> <B>-JB</B>)</A> <LI><A NAME="tex2html3763" HREF="node88.html">6.1.2 Equidistant conic projection (<B>-Jd</B> <B>-JD</B>)</A> <LI><A NAME="tex2html3764" HREF="node89.html">6.1.3 Lambert conic conformal projection (<B>-Jl</B> <B>-JL</B>)</A> <LI><A NAME="tex2html3765" HREF="node90.html">6.1.4 (American) polyconic projection (<B>-Jpoly</B> <B>-JPoly</B></A> </UL> <BR> <LI><A NAME="tex2html3766" HREF="node91.html">6.2 Azimuthal projections</A> <UL> <LI><A NAME="tex2html3767" HREF="node92.html">6.2.1 Lambert Azimuthal Equal-Area (<B>-Ja</B> <B>-JA</B>)</A> <UL> <LI><A NAME="tex2html3768" HREF="node93.html">6.2.1.1 Rectangular map</A> <LI><A NAME="tex2html3769" HREF="node94.html">6.2.1.2 Hemisphere map</A> </UL> <LI><A NAME="tex2html3770" HREF="node95.html">6.2.2 Stereographic Equal-Angle projection (<B>-Js</B> <B>-JS</B>)</A> <UL> <LI><A NAME="tex2html3771" HREF="node96.html">6.2.2.1 Polar Stereographic Map</A> <LI><A NAME="tex2html3772" HREF="node97.html">6.2.2.2 Rectangular stereographic map</A> <LI><A NAME="tex2html3773" HREF="node98.html">6.2.2.3 General stereographic map</A> </UL> <LI><A NAME="tex2html3774" HREF="node99.html">6.2.3 Perspective projection (<B>-Jg</B> <B>-JG</B>)</A> <LI><A NAME="tex2html3775" HREF="node100.html">6.2.4 Orthographic projection (<B>-Jg</B> <B>-JG</B>)</A> <LI><A NAME="tex2html3776" HREF="node101.html">6.2.5 Azimuthal Equidistant projection (<B>-Je</B> <B>-JE</B>)</A> <LI><A NAME="tex2html3777" HREF="node102.html">6.2.6 Gnomonic projection (<B>-Jf</B> <B>-JF</B>)</A> </UL> <BR> <LI><A NAME="tex2html3778" HREF="node103.html">6.3 Cylindrical projections</A> <UL> <LI><A NAME="tex2html3779" HREF="node104.html">6.3.1 Mercator projection (<B>-Jm</B> <B>-JM</B>)</A> <LI><A NAME="tex2html3780" HREF="node105.html">6.3.2 Transverse Mercator projection (<B>-Jt</B> <B>-JT</B>)</A> <LI><A NAME="tex2html3781" HREF="node106.html">6.3.3 Universal Transverse Mercator (UTM) projection (<B>-Ju</B> <B>-JU</B>)</A> <LI><A NAME="tex2html3782" HREF="node107.html">6.3.4 Oblique Mercator projection (<B>-Jo</B> <B>-JO</B>)</A> <LI><A NAME="tex2html3783" HREF="node108.html">6.3.5 Cassini cylindrical projection (<B>-Jc</B> <B>-JC</B>)</A> <LI><A NAME="tex2html3784" HREF="node109.html">6.3.6 Cylindrical equidistant projection (<B>-Jq</B> <B>-JQ</B>)</A> <LI><A NAME="tex2html3785" HREF="node110.html">6.3.7 Cylindrical equal-area projections (<B>-Jy</B> <B>-JY</B>)</A> <LI><A NAME="tex2html3786" HREF="node111.html">6.3.8 Miller Cylindrical projection (<B>-Jj</B> <B>-JJ</B>)</A> <LI><A NAME="tex2html3787" HREF="node112.html">6.3.9 Cylindrical stereographic projections (<B>-Jcyl_stere</B> <B>-JCyl_stere</B>)</A> </UL> <BR> <LI><A NAME="tex2html3788" HREF="node113.html">6.4 Miscellaneous projections</A> <UL> <LI><A NAME="tex2html3789" HREF="node114.html">6.4.1 Hammer projection (<B>-Jh</B> <B>-JH</B>)</A> <LI><A NAME="tex2html3790" HREF="node115.html">6.4.2 Mollweide projection (<B>-Jw</B> <B>-JW</B>)</A> <LI><A NAME="tex2html3791" HREF="node116.html">6.4.3 Winkel Tripel projection (<B>-Jr</B> <B>-JR</B>)</A> <LI><A NAME="tex2html3792" HREF="node117.html">6.4.4 Robinson projection (<B>-Jn</B> <B>-JN</B>)</A> <LI><A NAME="tex2html3793" HREF="node118.html">6.4.5 Eckert IV and VI projection (<B>-Jk</B> <B>-JK</B>)</A> <LI><A NAME="tex2html3794" HREF="node119.html">6.4.6 Sinusoidal projection (<B>-Ji</B> <B>-JI</B>)</A> <LI><A NAME="tex2html3795" HREF="node120.html">6.4.7 Van der Grinten projection (<B>-Jv</B> <B>-JV</B>)</A> </UL></UL> <!--End of Table of Child-Links--> <HR> <!--Navigation Panel--> <A NAME="tex2html3759" HREF="node86.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> <A NAME="tex2html3753" HREF="GMT_Docs.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> <A NAME="tex2html3747" HREF="node84.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> <A NAME="tex2html3755" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> <A NAME="tex2html3757" HREF="node256.html"> <IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.png"></A> <BR> <B> Next:</B> <A NAME="tex2html3760" HREF="node86.html">6.1 Conic projections</A> <B> Up:</B> <A NAME="tex2html3754" HREF="GMT_Docs.html">GMT - Technical Reference</A> <B> Previous:</B> <A NAME="tex2html3748" HREF="node84.html">5.2 Linear projection with</A> <B> <A NAME="tex2html3756" HREF="node1.html">Contents</A></B> <B> <A NAME="tex2html3758" HREF="node256.html">Index</A></B> <!--End of Navigation Panel--> <ADDRESS> Paul Wessel 2010-07-14 </ADDRESS> </BODY> </HTML>