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<H3><A NAME="SECTION003034300000000000000">
Determination of the Dispersion Coefficients</A>
</H3>
<P>
The command <TT>CALIBRATE/LONG</TT> determines the dispersion relation
for each row of the spectrum. In addition, a bivariate dispersion
relation is computed if the keyword
<!-- MATH: $\fbox{TWODOPT}$ -->
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is set to
<TT>YES</TT>, as in:
<BR> <BR>
Midas...> <TT>SET/LONG TWODOPT=YES</TT> <BR>
Midas...> <TT>CALIBRATE/LONG</TT> <BR>
<P>
The command <TT>CALIBRATE/LONG</TT> determines row-by-row
polynomial solutions of degree
<!-- MATH: $\fbox{DCX(1)}$ -->
<IMG
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SRC="img1035.gif"
ALT="\fbox{DCX(1)}">
stored in the
table <B>coerbr.tbl</B> and fits a 2-D
polynomial of degree
<!-- MATH: $\fbox{DCX(1),DCX(2)}$ -->
<IMG
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SRC="img1036.gif"
ALT="\fbox{DCX(1),DCX(2)}">
to the lines
with entries in columns :X, :Y, and :WAVE of table <B>line.tbl</B>.
The coefficients of the 2D polynomial are stored in
the keyword
<!-- MATH: $\fbox{KEYLONGD}$ -->
<IMG
WIDTH="143" HEIGHT="29" ALIGN="BOTTOM" BORDER="0"
SRC="img1037.gif"
ALT="\fbox{KEYLONGD}">.
The program performs a final oulier rejection which eliminates all
lines with residuals larger than
<!-- MATH: $\fbox{TOL}$ -->
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pixels (if <TT>TOL</TT> is
positive). However the minimum number of lines in any given row will be
<!-- MATH: $\fbox{DCX(1)}$ -->
<IMG
WIDTH="90" HEIGHT="36" ALIGN="BOTTOM" BORDER="0"
SRC="img1039.gif"
ALT="\fbox{DCX(1)}">+2. If this number cannot be obtained, a polynomial
of lower order will be fitted. Three more columns are added to
the table <B>line.tbl</B>:
<P>
<TABLE CELLPADDING=3>
<TR><TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">:WAVE</TD>
<TD ALIGN="LEFT">identified wavelength</TD>
</TR>
<TR><TD ALIGN="LEFT">:WAVEC</TD>
<TD ALIGN="LEFT">wavelength computed from polynomial fit</TD>
</TR>
<TR><TD ALIGN="LEFT">:RESIDUAL</TD>
<TD ALIGN="LEFT">(= :WAVEC - :WAVE) Residual of polynomial fit from</TD>
</TR>
<TR><TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT">the tabulated wavelength)</TD>
</TR>
</TABLE>
<P>
<BLOCKQUOTE>
<DIV ALIGN="CENTER">
<B>Note</DIV>
<I>For a proper calibration, images should preferably have positive
step descriptors and the wavelength should increase from left to
right.</I></B></BLOCKQUOTE>
<P>
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-15</I>
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