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RESAMPLE

        ANALYSE\RESAMPLE NX Xref Xval Xinc UNIT [shape] [width] [/FFT]

    This  command  resamples a given spectrum on a specified X axis in given
    unit. The arguments are:
      NX    the number of channels desired
      Xref  the new reference channel
      Xval  the value at the reference channel
      Xinc  the new channel separation
      UNIT  either CHANNEL, VELOCITY or FREQUENCY to indicate the units used
        for Xval and Xinc.
      SHAPE  (optional)  a keyword for the frequency response of the synthe-
        sized channels:
          - TBOX means a rectangular function in the delay  domain,  as  for
            unsmoothed correlator channels (sin(pi.x)/(pi.x) in the frequen-
            cy domain)
          - TPAR means a parabolic function in  the  delay  domain,  as  for
            smoothed correlator channels (smoothing function used at Plateau
            de Bure)
          - FBOX means a rectangular function in the  frequency  domain  (as
            for filterbank channels)
          - FTRIANGLE  means  a  triangular function in the frequency domain
            (as for filterbank channels, Hanning smoothed)
        By default the shape of the output channels is the same as the shape
        of the input channels.
      WIDTH  (optional)  the  width  of  the output channels in units of the
        channel separation. The default (and minimum value) is 1.

    /FFT
        The resampling is done in the delay domain and the data are  Fourier
        transformed.   The  Fourier transform is divided by the transform of
        the input channel shape, then extrapolated by zeroes (if  interpola-
        tion  in the frequency domain is required), multiplied by the trans-
        form of the desired channel shape, and finally transformed  back  to
        frequency  domain. The output channel separation usually needs to be
        slightly rounded (to enable use of the FFT, the input spectrum  must
        contain a round number of output channels). To obtain an exact chan-
        nel separation, the NOFFT option is necessary.

    The WIDTH parameter is used to provide an oversampled output spectrum if
    needed.

    The  shape of the input channels is derived from the backend number read
    in the telescope name for IRAM-30m  spectra:  TBOX  for  autocorrelator,
    FBOX for other (filter) backends. Otherwise, rectangular filter channels
    are assumed.


Gildas manager 2011-09-07