Documentation on zeemap

Task: zeemap
Purpose: Map the magnetic field from I and V cubes
Categories: profile analysis

        ZEEMAP tries to find the line-of-sight magnetic field splitting 
        a transition by measuring the shift in the line owing to the Zeeman 
        effect.

Key: iin
        Stokes I spectral cube, with axes in order Channel, X, Y.

Key: vin
        Stokes V spectral cube, with axes in order Channel, X, Y.

Key: b
        Output file name for Line-of-sight magnetic field.

Key: g
        Output file name for amount of residual I found in V (FIT only)

Key: d
        Output file name for the derivative of I/2 spectrum (DIV only)

Key: be
        Output file name for the error in B (DIV only)

Key: blc
        Bottom left corner of box to be fit

Key: trc
        Top right corner of box to be fit

Key: freq
        Frequency of line in GHz. This is used to determine amount of
        splitting per Gauss.

Key: op
        Operation code. Possible values are ``div'' and ``fit''. For
        ``div'', the line shift is determined by dividing V by the
        derivative of I/2. For ``fit'', the line shift is determined
        by fitting of the derivative of I and I to V.

Key: cutoff
        For ``div'', the division will not be performed unless the
        derivative of I/2 is greater than cutoff.
        For ``fit'', the fit will not be performed unless one or more
        channels in the I spectrum is larger in absolute
        value than cutoff.

Key: vrms
        RMS deviation in V spectrum in a signal free area.  This can easily
        be gotten using histo.  Used for calculating error in B for op=div.

Key: mode
        This determines the algorithms used, if operation=``fit''. It
        can consist of several flags:
         l  Include leakage term.
         2  Use 2 sided derivative approximation.
         m  Use maximum likelihood technique.
         x  Perform extra checks for better solutions, when
            using the maximum likelihood technique.
        Default mode=2m

Key: y corlen
        Correlation length.  Selected window must be divisible by this
        number, which is the number of pixels over which you think the
        magnetic field might be constant.  Default is 1, try maybe 2 or 4.