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Determination of the Dispersion Coefficients

The command CALIBRATE/LONG determines the dispersion relation for each row of the spectrum. In addition, a bivariate dispersion relation is computed if the keyword \fbox{TWODOPT} is set to YES, as in:

Midas...> SET/LONG TWODOPT=YES
Midas...> CALIBRATE/LONG

The command CALIBRATE/LONG determines row-by-row polynomial solutions of degree \fbox{DCX(1)} stored in the table coerbr.tbl and fits a 2-D polynomial of degree \fbox{DCX(1),DCX(2)} to the lines with entries in columns :X, :Y, and :WAVE of table line.tbl. The coefficients of the 2D polynomial are stored in the keyword \fbox{KEYLONGD}. The program performs a final oulier rejection which eliminates all lines with residuals larger than \fbox{TOL} pixels (if TOL is positive). However the minimum number of lines in any given row will be \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 line.tbl:

   
:WAVE identified wavelength
:WAVEC wavelength computed from polynomial fit
:RESIDUAL (= :WAVEC - :WAVE) Residual of polynomial fit from
  the tabulated wavelength)

Note
For a proper calibration, images should preferably have positive step descriptors and the wavelength should increase from left to right.


next up previous contents
Next: Possible Graphical Verifications Up: Getting the Dispersion Solution Previous: Line Identification
http://www.eso.org/midas/midas-support.html
1999-06-15