<param type="any" name="width" subparam="true"><shortdescription>Channel width of the output visibilities. Used for regridding, together with \'start\', and \'nchan\'. It can be in different units, depending on the regridding mode: number of input channels (mode=\'channel\'), velocity (mode=\'velocity\'), or frequency (mode=\'frequency\'. Example values: \'2\', \'1.0km/s\', \'1.0kHz\', for channel, velocity, and frequency modes, respectively.</shortdescription><description>Channel width of the output visibilities. Used for regridding, together with \'start\', and \'nchan\'. It can be in different units, depending on the regridding mode: number of input channels (mode=\'channel\'), velocity (mode=\'velocity\'), or frequency (mode=\'frequency\'. Example values: \'2\', \'1.0km/s\', \'1.0kHz\', for channel, velocity, and frequency modes, respectively.</description>
<casaxml xsi:schemaLocation="http://casa.nrao.edu/schema/casa.xsd file:///opt/casa/code/xmlcasa/xml/casa.xsd" xmlns="http://casa.nrao.edu/schema/psetTypes.html" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<task type="function" name="cvel" category="manipulation">
<shortdescription>regrid an MS to a new spectral window / channel structure or frame</shortdescription>
The intent of cvel 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 cvel.
If cvel has already established the grid that is desired for the
imaging, clean should be run with exactly the same frequency/velocity
parameters as used in cvel in order to avoid additional regridding in
Hanning smoothing is optionally offered in cvel, 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.
<param type="path" name="vis" mustexist="true"><shortdescription>Name of input measurement set</shortdescription><description>Name of input measurement set</description>
<param type="string" name="outputvis"><shortdescription>Name of output measurement set</shortdescription><description>Name of output measurement set</description>
<param type="bool" name="passall"><shortdescription>Pass through (write to output MS) non-selected data with no change</shortdescription><description>Pass through (write to output MS) non-selected data with no change</description>
<param type="any" name="field"><shortdescription>Select field using field id(s) or field name(s)</shortdescription><description>Select field using field id(s) or field name(s)</description>
<type>string</type><type>stringVec</type><type>int</type><type>intVec</type>
<param type="any" name="spw"><shortdescription>Select spectral window/channels</shortdescription><description>Select spectral window/channels</description>
<type>string</type><type>stringVec</type><type>int</type><type>intVec</type>
<param type="bool" name="selectdata"><shortdescription>Other data selection parameters</shortdescription><description>Other data selection parameters</description>