RESAMPLE

 

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

    This command resamples a  given  spectrum  on  a  specified  grid.   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 VELOCITY or FREQUENCY to indicate the units used for Xval
        and Xinc.
      SHAPE  (optional)  a  keyword  for  the  frequency  response  of   the
        synthesized channels:
          - TBOX means a rectangular function in the delay  domain,  as  for
            unsmoothed   correlator   channels   (sin(pi.x)/(pi.x)   in  the
            frequency 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.
    The resampling is done in the delay domain, and  the  data  are  Fourier
    transformed, unless the option /NOFFT is used.  The Fourier transform is
    divided by the transform of the input channel shape,  then  extrapolated
    by  zeroes  (if  interpolation  in  the  frequency  domain is required),
    multiplied by the transform 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  channel  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.

    Resample may be used on on-the-fly scans too.