The intent of cvel2 is to transform channel labels and the visibilities to a spectral reference frame which is appropriatefor 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 theimaging, clean should be run with exactly the same frequency/velocity parameters as used in cvel2 in order to avoid additional regridding in clean.

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 itwill create an output Multi-MS too.

NOTE: The parameter passall is not supported in cvel2. The user may achievethe same results of passall=True by splitting out the data that will notbe 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.