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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