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<HTML>
<HEAD>
<TITLE>Contour level selection</TITLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF" TEXT="#000000">
<P><A NAME="contourlevels"></A>
<font size="+2" color="green">Contour level selection</font></P>
<P>
<TABLE border="1" cols="2" frame="box" rules="cols" width="608">
<TR>
<TD width="15%" valign="top"><B>Syntax</B>:</TD>
<TD width="85%" valign="top"><CODE>
CONTOUR { x y } v nctr { min { incr }}<br />
CONTOUR\SPECIFIC { x y } v lvls</CODE>
</TD></TR>
</TABLE>
<P>
By default, the number of contours, <CODE>nctr</CODE>, must be provided.
If <CODE>nctr > 0</CODE> and the increment is
not specified, the actual number of contours drawn may not be the same as
the number that was asked for, since "nice" contour levels will be
selected and the range of values may not be neatly divisible by the
requested number. If the minimum is provided, but not the increment, a
"nice" value close to <CODE>min</CODE> will be
used instead of the actual data minimum. If the minimum and the increment
are both specified, those exact values will be used for the contour
levels.</P>
<P>
<font size="+1" color="green">Specific contour levels</font></P>
<P>
Specific contour levels can be requested by using the <CODE>\SPECIFIC</CODE>
qualifier. In this case, the vector <CODE>lvls</CODE> should contain the desired contour levels.</P>
<P>
<font size="+1" color="green">Exact contour levels</font></P>
<P>
Exact contour levels can be requested in three ways.</P>
<UL>
<LI>Use the <CODE>\SPECIFIC</CODE> qualifier and
enter a vector containing the desired levels.</li>
<LI>Specify the minimum contour level, <CODE>min</CODE>, and the contour level
increment, <CODE>inc</CODE>. This produces a set of equally spaced contour levels,<BR />
<CODE>[min; min+inc; min+2*inc; ...; min+nctr*inc]</CODE>.</li>
<LI>Specify a negative number of contours,
<CODE>nctr < 0</CODE>. This
produces a set of equally spaced contour levels, as above, using the actual
data minimum and the actual data maximum.</li>
</UL>
<P>
<font size="+1" color="green">Zooming in</font></P>
<P>
When the minimum and maximum contour levels are to be determined, by default,
the entire range of the data is used. If the
<CODE>\PARTIAL</CODE> qualifier is used, the minimum and maximum contour levels will be
determined by the region contained within the axes. Thus, to zoom in on a
particular region for more detail, pre-set the axis scales, using the
<CODE><a href="../ScalesCommand/scalescommand.htm">SCALES</a></CODE>
command, before entering the <CODE>CONTOUR</CODE>
command. Of course, the <CODE>\PARTIAL</CODE>
qualifier does not apply when you request specific contour levels.</P>
<P>
<a href="contourcommand.htm"><img src="../shadow_left.gif">
<font size="+1" color="olive">CONTOUR command</font></a><br />
<a href="colours.htm"><img src="../shadow_right.gif">
<font size="+1" color="olive">Contour level colour</font></a>
</P>
</body>
</html>
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