<!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>6.3.4 Oblique Mercator projection (-Jo -JO)</TITLE> <META NAME="description" CONTENT="6.3.4 Oblique Mercator projection (-Jo -JO)"> <META NAME="keywords" CONTENT="GMT_Docs"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META NAME="Generator" CONTENT="LaTeX2HTML v2002-2-1"> <META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css"> <LINK REL="STYLESHEET" HREF="GMT_Docs.css"> <LINK REL="next" HREF="node110.html"> <LINK REL="previous" HREF="node108.html"> <LINK REL="up" HREF="node105.html"> <LINK REL="next" HREF="node110.html"> </HEAD> <BODY bgcolor="#ffffff"> <!--Navigation Panel--> <A NAME="tex2html4225" HREF="node110.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> <A NAME="tex2html4219" HREF="node105.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> <A NAME="tex2html4213" HREF="node108.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> <A NAME="tex2html4221" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> <A NAME="tex2html4223" HREF="node258.html"> <IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.png"></A> <BR> <B> Next:</B> <A NAME="tex2html4226" HREF="node110.html">6.3.5 Cassini cylindrical projection</A> <B> Up:</B> <A NAME="tex2html4220" HREF="node105.html">6.3 Cylindrical projections</A> <B> Previous:</B> <A NAME="tex2html4214" HREF="node108.html">6.3.3 Universal Transverse Mercator</A> <B> <A NAME="tex2html4222" HREF="node1.html">Contents</A></B> <B> <A NAME="tex2html4224" HREF="node258.html">Index</A></B> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION001434000000000000000"> 6.3.4 Oblique Mercator projection (<B>-Jo</B> <B>-JO</B>)</A> </H2> <A NAME="23006"></A> <A NAME="23007"></A> <A NAME="23008"></A> <P> Oblique configurations of the cylinder give rise to the oblique Mercator projection. It is particularly useful when mapping regions of large lateral extent in an oblique direction. Both parallels and meridians are complex curves. The projection was developed in the early 1900s by several workers. Several parameters must be provided to define the projection. <A NAME="tex2html1370" HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> offers three different definitions: <P> <OL> <LI>Option <B>-Joa</B> or <B>-JOa</B>: <UL> <LI>Longitude and latitude of projection center. </LI> <LI>Azimuth of the oblique equator. </LI> <LI>Scale in inch/degree or 1:xxxxx along oblique equator (<B>-Joa</B>), or map width (<B>-JOa</B>). </LI> </UL> <P> </LI> <LI>Option <B>-Job</B> or <B>-JOb</B>: <UL> <LI>Longitude and latitude of projection center. </LI> <LI>Longitude and latitude of second point on oblique equator. </LI> <LI>Scale in inch/degree or 1:xxxxx along oblique equator (<B>-Job</B>), or map width (<B>-JOb</B>). </LI> </UL> <P> </LI> <LI>Option <B>-Joc</B> or <B>-JOc</B>: <UL> <LI>Longitude and latitude of projection center. </LI> <LI>Longitude and latitude of projection pole. </LI> <LI>Scale in inch/degree or 1:xxxxx along oblique equator (<B>-Joc</B>), or map width (<B>-JOc</B>). </LI> </UL> <P> </LI> </OL> <P> Our example was produced by the command <P> <BR CLEAR="ALL"> <HR> <BR> <PRE>pscoast -R270/20/305/25r -JOc280/25.5/22/69/4.8i -B10g5 -Di -A250 -Glightgray -Wthinnest -P \ -Tf301.5/23/0.4i/2 --HEADER_FONT_SIZE=8p --HEADER_OFFSET=0.05i > GMT_obl_merc.ps </PRE> <BR CLEAR="ALL"> <HR> <P> <DIV ALIGN="CENTER"><A NAME="fig:GMT_obl_merc"></A><A NAME="23525"></A> <TABLE> <CAPTION ALIGN="BOTTOM"><STRONG>Figure 6.19:</STRONG> Oblique Mercator map using <B>-Joc</B>. We make it clear which direction is North by adding a star rose with the <B>-T</B> option.</CAPTION> <TR><TD> <DIV ALIGN="CENTER"><IMG WIDTH="626" HEIGHT="419" ALIGN="BOTTOM" BORDER="0" SRC="img140.png" ALT="\includegraphics{scripts/GMT_obl_merc}"></DIV></TD></TR> </TABLE> </DIV> <P> It uses definition 3 for an oblique view of some Caribbean islands. Note that we define our region using the rectangular system described earlier. If we do not append an ``r'' to the <B>-R</B> string then the information provided with the <B>-R</B> option is assumed to be oblique degrees about the projection center rather than the usual geographic coordinates. This interpretation is chosen since in general the parallels and meridians are not very suitable as map boundaries. <P> <A NAME="23010"></A> <A NAME="23011"></A> <A NAME="23012"></A> <P> <HR> <!--Navigation Panel--> <A NAME="tex2html4225" HREF="node110.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> <A NAME="tex2html4219" HREF="node105.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> <A NAME="tex2html4213" HREF="node108.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> <A NAME="tex2html4221" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> <A NAME="tex2html4223" HREF="node258.html"> <IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.png"></A> <BR> <B> Next:</B> <A NAME="tex2html4226" HREF="node110.html">6.3.5 Cassini cylindrical projection</A> <B> Up:</B> <A NAME="tex2html4220" HREF="node105.html">6.3 Cylindrical projections</A> <B> Previous:</B> <A NAME="tex2html4214" HREF="node108.html">6.3.3 Universal Transverse Mercator</A> <B> <A NAME="tex2html4222" HREF="node1.html">Contents</A></B> <B> <A NAME="tex2html4224" HREF="node258.html">Index</A></B> <!--End of Navigation Panel--> <ADDRESS> Paul Wessel 2011-02-27 </ADDRESS> </BODY> </HTML>