<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="mstransform" category="manipulation">
<shortdescription>Split the MS, combine/separate/regrid spws and do channel and time averaging</shortdescription>
The task mstransform can do the same functionalities available
in cvel, partition, hanningsmooth and split without the need to read and write
the output to disk multiple times. The main features of this task
* take an input MS or Multi-MS (MMS)
* ability to create an output MS or MMS
* spw combination and separation
* channel averaging taking flags and weights into account
* time averaging taking flags and weights into account
* reference frame transformation
All these transformations will be applied on the fly without any writing to
disk to optimize I/O. The user can ask to create a Multi-MS in parallel using CASA's
cluster infrastructure using the parameter createmms. See MPIInterface
for more information on the cluster infrastructure.
This task is implemented in a modular way to preserve the functionalities
available in the replaced tasks. One can choose which functionality to apply
or apply all of them by setting the corresponding parameters to True. Note
that there is an order in which the transformations are applied to the data that
makes logical sense on the point of view of the data analysis.
This task can create a multi-MS as the output. General selection
parameters are included, and one or all of the various data columns
(DATA, LAG_DATA and/or FLOAT_DATA, and possibly MODEL_DATA and/or
CORRECTED_DATA) can be selected. It can also be used to create a normal
MS, split-based on the given data selection parameters.
The mstransform task creates a Multi-MS in parallel, using the CASA MPI framework.
The user should start CASA as follows in order to run it in parallel.
1) Start CASA on a single node with 8 engines. The first engine will be used as the
MPIClient, where the user will see the CASA prompt. All other engines will be used
as MPIServers and will process the data in parallel.
mpicasa -n 8 casa --nogui --log2term
2) Running on a group of nodes in a cluster.
mpicasa -hostfile user_hostfile casa ....
where user_hostfile contains the names of the nodes and the number of engines to use
in each one of them. Example:
If CASA is started without mpicasa, it is still possible to create an MMS, but
the processing will be done in sequential.
The resulting WEIGHT_SPECTRUM produced by mstransform is in the statistical
sense correct for the simple cases of channel average and time average, but not for
the general re-gridding case, in which the error propagation formulas applicable for
WEIGHT_SPECTRUM are yet to be defined. Currently, as in cvel and in the imager,
WEIGHT_SPECTRUM is transformed in the same way as the other data columns.