Manipulating Visibilities with MStransform

Regridding visibilities with the task mstransform

mstransform is a multipurpose task that provides all the functionality of split, partition, cvel, hanningsmooth, uvcontsub and applycal with the possibility of applying each of these transformations separately or together in an in-memory pipeline, thus avoiding unnecessary I/O steps. The list of transformations that mstransform can apply is as follows:

  1. Data selection and re-indexing
  2. Data partitioning (create output Multi-MS)
  3. On-the-fly calibration (via “Cal Library”)
  4. Time averaging (weighted and baseline dependent)
  5. UV continuum subtraction
  6. Combination of spectral windows
  7. Channel averaging (weighted)
  8. Hanning smoothing
  9. Spectral regridding and reference frame transformation
  10. Separation of spectral windows

Notice that the order in the above list is not arbitrary. When various transformations are applied on the data using mstransform, the order in which the transformations are piped one after the other is the one shown in the above list. These operations are described in the sections that follow.

Besides mstransform in itself, there are a series of tasks which perform only the individual operations: split, hanningsmooth and cvel2. Under the hood these are all based on the mstransform framework; they are provided to facilitate back compatibility, and for simplicity in cases where only the simpler operations are needed.  Notice that as of CASA 4.6, the mstransform based versions of split and hanningsmooth are the default ones, whereas cvel still is based on the old implementation by default, and the cvel2 interface points to the mstransform implementation.