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Basic Information on line
The ``line'' parameter determines the channels that are to be processed
from a uv data-set. The parameter value consists of a string
followed by up to four numbers. Defaults are used for any missing
trailing portion of the parameter value.
A uv data-set can have correlations from either (or both) a spectral
or a wideband (continuum) correlator. Both the spectral and wideband
correlators produce multiple correlations (channels). The string
part of the line parameter is used to select the spectral or wideband
channels. It may be one of:
"channel" Spectral channels.
"wide" Wideband (continuum) channels.
"velocity" Spectral channels, resampled at equal increments in
velocity (using the radio definition). The resampling
involves a weighted average of the spectral channels.
This is useful if the source was not Doppler tracked
"felocity" Similar to "velocity", except that the parameters are
given using the optical velocity definition.
Generally the default is "channel" if the data-set has spectral
channel data, and "wide" otherwise.
The four numbers that accompany the string give:
nchan, start, width, step
These four numbers specify which channels to select from the input
dataset and how to combine them to produce the output channels that
the Miriad task will work on.
nchan is the number of output channels produced. Generally it
defaults to the number of input channels.
start is the first channel from input dataset that is to be used.
It defaults to 1 (i.e. first channel).
width gives the number of input channels to average together to
produce a single output channel. It defaults to 1.
step gives the increment between selected input channels. It
defaults to the value of "width".
For "velocity" linetype, the start, width and step parameters are
given in km/s. The output channels are centered on velocities:
start, start+step, start+2*step, etc.
The `line' parameter interacts with the "select=window" selection
for "channel" and "velocity"/"felocity" linetypes. See the help on
select for more information.
selects 10 output channels, being input spectral channels 1 to 10.
selects 10 output channels, starting at input channel 8, and skipping
every second input channel, whereas
selects 10 output channels, again starting at input channel 8, but
each of the output channels consists of the average of two of the
input channels. Finally
resamples the spectral data in velocity, to give 10 channels of width
1 km/s. The channels are centered at -10.0,-9.0,-8.0, etc, km/s.
Generated by firstname.lastname@example.org on 26 May 2011