<casaxml xsi:schemaLocation="http://casa.nrao.edu/schema/casa.xsd file:///opt/casa/code/xmlcasa/xml/casa.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://casa.nrao.edu/schema/psetTypes.html">
<task visibility="experimental" category="manipulation" name="cvel2" type="function">
<shortdescription>Regrid an MS or MMS to a new spectral window, channel structure or frame</shortdescription>
The intent of cvel2 is to transform channel labels and the
visibilities to a spectral reference frame which is appropriate for
the science analysis, e.g. from TOPO to LSRK to correct for Doppler
shifts throughout the time of the observation. Naturally, this will
change the shape of the spectral feature to some extent. According to
the Nyquist theorem you should oversample a spectrum with twice the
numbers of channels to retain the shape. Based on some tests, however,
we recommend to observe with at least 3-4 times the number of channels
for each significant spectral feature (like 3-4 times the
linewidth). This will minimize regridding artifacts in cvel2.
If cvel2 has already established the grid that is desired for the
imaging, tclean should be run with exactly the same frequency/velocity
parameters as used in cvel2 in order to avoid additional regridding in
Hanning smoothing is optionally offered in cvel2, but tests have shown
that already the regridding process itself, if it involved a
transformation from TOPO to a non-terrestrial reference frame, implies
some smoothing (due to channel interpolation) such that Hanning
smoothing may not be necessary.
This version of cvel2 also supports Multi-MS input, in which case it
will create an output Multi-MS too.
The parameter passall is not supported in cvel2. The user may
achieve the same results of passall=True by splitting out the data
that will not be regridded with cvel2 and concatenate regridded
and non-regridded sets at the end. In the case of Multi-MS input,
the user should use virtualconcat to achieve a concatenated MMS.
<param mustexist="true" name="vis" type="path">
<shortdescription>Name of input visibility file</shortdescription>
<description>Name of input visibility file
Example: vis='ngc5921.ms'
<param name="outputvis" type="string">
<shortdescription>Name of output visibility file</shortdescription>
<description>Name of output visibility file or Multi-MS
Example: vis='ngc5921_out.ms'
<param name="keepmms" type="bool">
<shortdescription>Create a Multi-MS as the output if the input is a Multi-MS</shortdescription>