<!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>3.2 Gridding of arbitrarily spaced data</TITLE> <META NAME="description" CONTENT="3.2 Gridding of arbitrarily spaced data"> <META NAME="keywords" CONTENT="GMT_Tutorial"> <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_Tutorial.css"> <LINK REL="next" HREF="node48.html"> <LINK REL="previous" HREF="node41.html"> <LINK REL="up" HREF="node40.html"> <LINK REL="next" HREF="node44.html"> </HEAD> <BODY bgcolor="#ffffff"> <!--Navigation Panel--> <A NAME="tex2html1002" HREF="node44.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> <A NAME="tex2html996" HREF="node40.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> <A NAME="tex2html990" HREF="node42.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> <A NAME="tex2html998" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> <A NAME="tex2html1000" HREF="node63.html"> <IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.png"></A> <BR> <B> Next:</B> <A NAME="tex2html1003" HREF="node44.html">3.2.1 Nearest neighbor gridding</A> <B> Up:</B> <A NAME="tex2html997" HREF="node40.html">3. SESSION THREE</A> <B> Previous:</B> <A NAME="tex2html991" HREF="node42.html">3.1.1 Exercises</A> <B> <A NAME="tex2html999" HREF="node1.html">Contents</A></B> <B> <A NAME="tex2html1001" HREF="node63.html">Index</A></B> <BR> <BR> <!--End of Navigation Panel--> <H1><A NAME="SECTION00520000000000000000"> 3.2 Gridding of arbitrarily spaced data</A> </H1> <P> Except in the situation above when a grid file is available, we must convert our data to the right format readable by <A NAME="tex2html170" HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> before we can make contour plots and color-coded images. We distinguish between two scenarios: <P> <OL> <LI>The (<I>x</I>, <I>y</I>, <I>z</I>) data are available on a regular lattice grid. <P> </LI> <LI>The (<I>x</I>, <I>y</I>, <I>z</I>) data are distributed unevenly in the plane. <P> </LI> </OL> <P> The former situation may require a simple reformatting (using <A NAME="tex2html171" HREF="../man/xyz2grd.html"><I><B>xyz2grd</B></I></A><A NAME="2337"></A>), while the latter must be interpolated onto a regular lattice; this process is known as gridding. <A NAME="tex2html172" HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> supports three different approaches to gridding; here, we will briefly discuss the two most common techniques. <P> All <A NAME="tex2html173" HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> gridding programs have in common the requirement that the user must specify the grid domain and output filename: <BR> <P> <TABLE CELLPADDING=3> <TR><TH ALIGN="LEFT"><B>-R</B><I>xmin</I>/<I>xmax</I>/<I>ymin</I>/<I>ymax</I></TH> <TD ALIGN="LEFT">The desired grid extent</TD> </TR> <TR><TH ALIGN="LEFT"><B>-I</B><I>xinc</I>[<B>m</B><IMG WIDTH="8" HEIGHT="31" ALIGN="MIDDLE" BORDER="0" SRC="img1.png" ALT="$\vert$"><B>c</B>][/<I>yinc</I>[<B>m</B><IMG WIDTH="8" HEIGHT="31" ALIGN="MIDDLE" BORDER="0" SRC="img1.png" ALT="$\vert$"><B>c</B>]]</TH> <TD ALIGN="LEFT">The grid spacing (append <B>m</B> or <B>c</B> for minutes or seconds of arc)</TD> </TR> <TR><TH ALIGN="LEFT"><B>-G</B><I>gridfile</I></TH> <TD ALIGN="LEFT">The output grid filename</TD> </TR> </TABLE> <P> <BR><HR> <!--Table of Child-Links--> <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A> <UL> <LI><A NAME="tex2html1004" HREF="node44.html">3.2.1 Nearest neighbor gridding</A> <UL> <LI><A NAME="tex2html1005" HREF="node45.html">3.2.1.1 Exercises</A> </UL> <BR> <LI><A NAME="tex2html1006" HREF="node46.html">3.2.2 Gridding with Splines in Tension</A> <LI><A NAME="tex2html1007" HREF="node47.html">3.2.3 Preprocessing</A> </UL> <!--End of Table of Child-Links--> <HR> <!--Navigation Panel--> <A NAME="tex2html1002" HREF="node44.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> <A NAME="tex2html996" HREF="node40.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> <A NAME="tex2html990" HREF="node42.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> <A NAME="tex2html998" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> <A NAME="tex2html1000" HREF="node63.html"> <IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.png"></A> <BR> <B> Next:</B> <A NAME="tex2html1003" HREF="node44.html">3.2.1 Nearest neighbor gridding</A> <B> Up:</B> <A NAME="tex2html997" HREF="node40.html">3. SESSION THREE</A> <B> Previous:</B> <A NAME="tex2html991" HREF="node42.html">3.1.1 Exercises</A> <B> <A NAME="tex2html999" HREF="node1.html">Contents</A></B> <B> <A NAME="tex2html1001" HREF="node63.html">Index</A></B> <!--End of Navigation Panel--> <ADDRESS> Paul Wessel 2010-01-14 </ADDRESS> </BODY> </HTML>
