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<H2><A NAME="SECTION001721000000000000000"></A>
<A NAME="13178"></A>
<BR>
B.2.1 File contents
</H2>
<P>
The default 2-D binary netCDF grdfile in <A NAME="tex2html577"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> has several attributes.
The <A NAME="tex2html578"
HREF="../grdedit.html"><I><B>grdedit</B></I></A><A NAME="13471"></A> utility program will allow you to edit parts of
the header of an existing grdfile. The attributes listed in Table <A HREF="node114.html#tbl:grdheader">B.1</A>
are contained within the header record in the order given (except the <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-array which
is not part of the header structure, but makes up the rest of the file).
<P>
<BR><P></P>
<DIV ALIGN="CENTER"><A NAME="13231"></A>
<TABLE>
<CAPTION><STRONG>Table B.1:</STRONG>
<A NAME="tex2html574"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> gridded file header record</CAPTION>
<TR><TD>
<DIV ALIGN="CENTER"><TABLE CELLPADDING=3 BORDER="1">
<TR><TD ALIGN="CENTER" COLSPAN=1><I>Parameter</I></TD>
<TD ALIGN="CENTER" COLSPAN=1><I>Description</I></TD>
</TR>
<TR><TD ALIGN="LEFT"><B>int</B> <I>nx</I></TD>
<TD ALIGN="LEFT">Number of nodes in the <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img1.gif"
ALT="$x$">-dimension</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>int</B> <I>ny</I></TD>
<TD ALIGN="LEFT">Number of nodes in the y-dimension</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>int</B> <I>node_offset</I></TD>
<TD ALIGN="LEFT">0 for grid line registration, 1 for pixel registration</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>x_min</I></TD>
<TD ALIGN="LEFT">Minimum <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img1.gif"
ALT="$x$">-value of region</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>x_max</I></TD>
<TD ALIGN="LEFT">Maximum <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img1.gif"
ALT="$x$">-value of region</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>y_min</I></TD>
<TD ALIGN="LEFT">Minimum <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img18.gif"
ALT="$y$">-value of region</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>y_max</I></TD>
<TD ALIGN="LEFT">Maximum <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img18.gif"
ALT="$y$">-value of region</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>z_min</I></TD>
<TD ALIGN="LEFT">Minimum <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-value in data set</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>z_max</I></TD>
<TD ALIGN="LEFT">Maximum <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-value in data set</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>x_inc</I></TD>
<TD ALIGN="LEFT">Node spacing in <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img1.gif"
ALT="$x$">-dimension</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>y_inc</I></TD>
<TD ALIGN="LEFT">Node spacing in <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img18.gif"
ALT="$y$">-dimension</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>z_scale_factor</I></TD>
<TD ALIGN="LEFT">Factor to multiply <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-values after read</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>double</B> <I>z_add_offset</I></TD>
<TD ALIGN="LEFT">Offset to add to scaled <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-values</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>char</B> <I>x_units</I>[80]</TD>
<TD ALIGN="LEFT">Units of the <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img1.gif"
ALT="$x$">-dimension</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>char</B> <I>y_units</I>[80]</TD>
<TD ALIGN="LEFT">Units of the <IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img18.gif"
ALT="$y$">-dimension</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>char</B> <I>z_units</I>[80]</TD>
<TD ALIGN="LEFT">Units of the <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-dimension</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>char</B> <I>title</I>[80]</TD>
<TD ALIGN="LEFT">Descriptive title of the data set</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>char</B> <I>command</I>[320]</TD>
<TD ALIGN="LEFT">Command line that produced the grdfile</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>char</B> <I>remark</I>[160]</TD>
<TD ALIGN="LEFT">Any additional comments</TD>
</TR>
<TR><TD ALIGN="LEFT"><B>float</B> <I>z</I>[nx*ny]</TD>
<TD ALIGN="LEFT">1-D array with <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-values in scanline format</TD>
</TR>
</TABLE>
</DIV>
<P>
<DIV ALIGN="CENTER">
<A NAME="tbl:grdheader"></A></DIV></TD></TR>
</TABLE>
</DIV><P></P>
<BR>
<P>
<A NAME="13234"></A>
<P>
<A NAME="tex2html579"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> version 3 also allows other formats to be read. In addition to
the default netCDF format it can use binary floating points, short
integers, bytes, and bits, as well as 8-bit Sun rasterfiles (colormap
ignored). Additional formats may be used by supplying read/write
functions and linking these with the <A NAME="tex2html580"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> libraries.
The source file <U>gmt_customio.c</U> has the information that
programmers will need to augment <A NAME="tex2html581"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> to read custom grdfiles. We
anticipate that the number of pre-programmed formats will increase as
enterprising users implement what they need.
<P>
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<ADDRESS>
Paul Wessel
2001-04-18
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