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<H2><A NAME="SECTION001922000000000000000"></A> 
<A NAME="29293"></A>
<A NAME="sec:node_registration"></A>
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B.2.2 Gridline and Pixel node registration
</H2>

<P>
Scanline format means that the data are stored in rows (<I>y</I> = constant)
going from the ``top'' (<IMG
 WIDTH="58" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
 SRC="img213.png"
 ALT="$y = y_{max}$"> (north)) to the ``bottom''
(<IMG
 WIDTH="56" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
 SRC="img214.png"
 ALT="$y = y_{min}$"> (south)).  Data within each row are ordered from
``left'' (<IMG
 WIDTH="56" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
 SRC="img215.png"
 ALT="$x = x_{min}$"> (west)) to ``right'' (<IMG
 WIDTH="58" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
 SRC="img216.png"
 ALT="$x = x_{max}$">
(east)).  The <I>node_offset</I> signals how the nodes are laid out.
The grid is always defined as the intersections of all <I>x</I>
( <!-- MATH
 $x = x_{min}, x_{min} + x_{inc}, x_{min} + 2 \cdot x_{inc}, \ldots, x_{max}$
 -->
<IMG
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 SRC="img217.png"
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and <I>y</I> ( <!-- MATH
 $y = y_{min}, y_{min} + y_{inc}, y_{min} + 2 \cdot y_{inc}, \ldots, y_{max}$
 -->
<IMG
 WIDTH="273" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
 SRC="img218.png"
 ALT="\( y = y_{min}, y_{min} + y_{inc}, y_{min} + 2 \cdot y_{inc}, \ldots, y_{max} \)"> )
lines.  The two scenarios differ in which area each data point
represents.
The default node registration in <A NAME="tex2html1664"
  HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> is gridline node registration.  Most
programs can handle both types, and for some programs like <A NAME="tex2html1665"
  HREF="../man/grdimage.html"><I><B>grdimage</B></I></A><A NAME="29656"></A>
a pixel registered file makes more sense.  Utility programs like
<A NAME="tex2html1666"
  HREF="../man/grdsample.html"><I><B>grdsample</B></I></A><A NAME="29661"></A> and <A NAME="tex2html1667"
  HREF="../man/grdproject.html"><I><B>grdproject</B></I></A><A NAME="29666"></A> will allow you to convert
from one format to the other; <A NAME="tex2html1668"
  HREF="../man/grdedit.html"><I><B>grdedit</B></I></A><A NAME="29671"></A> can make changes to the grid header
and convert a pixel- to a gridline-registred grid, or <I>vice versa</I>.

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<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>

<UL>
<LI><A NAME="tex2html5241"
  HREF="node183.html">B.2.2.1 Gridline registration</A>
<LI><A NAME="tex2html5242"
  HREF="node184.html">B.2.2.2 Pixel registration</A>
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  HREF="node180.html">B.2 Grid files</A>
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<ADDRESS>
Paul Wessel
2010-07-14
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