vis -- Name of input visibility file
               default: none; example: vis='ngc5921.ms'    

       outputvis -- Name of output measurement set (required)
               default: none; example: vis='ngc5921-regridded.ms'    
       passall --  if False, data not meeting the selection is omitted/deleted
               or flagged (if in-row); if True, data not meeting the selection
               on field and spw is passed through without modification
           default: False; example:
               passall=False : only data from NGC5921 is included in output MS,
                         no data from other fields (e.g. 1331+305) is included
               passall=True : data from NGC5921 is transformed by cvel, all other
                         fields are passed through unchanged

       field -- Select fields in mosaic.  Use field id(s) or field name(s).
                  ['go listobs' to obtain the list id's or names]
              default: ''= all fields
              If field string is a non-negative integer, it is assumed to
                  be a field index otherwise, it is assumed to be a
          field name
              field='0~2'; field ids 0,1,2
              field='0,4,5~7'; field ids 0,4,5,6,7
              field='3C286,3C295'; field named 3C286 and 3C295
              field = '3,4C*'; field id 3, all names starting with 4C

       spw --Select spectral window/channels
              NOTE: This selects the data passed as the INPUT to mode
              default: ''=all spectral windows and channels
                spw='0~2,4'; spectral windows 0,1,2,4 (all channels)
                spw='0:5~61'; spw 0, channels 5 to 61
                spw='<2';   spectral windows less than 2 (i.e. 0,1)
                spw='0,10,3:3~45'; spw 0,10 all channels, spw 3,
                   channels 3 to 45.
                spw='0~2:2~6'; spw 0,1,2 with channels 2 through 6 in each.
                spw='0:0~10;15~60'; spectral window 0 with channels
                spw='0:0~10,1:20~30,2:1;2;3'; spw 0, channels 0-10,
                      spw 1, channels 20-30, and spw 2, channels, 1,2 and 3

       selectdata -- Other data selection parameters
              default: True

  >>> selectdata=True expandable parameters

              antenna -- Select data based on antenna/baseline
                  default: '' (all)
                  If antenna string is a non-negative integer, it is
             assumed to be an antenna index, otherwise, it is
             considered an antenna name.
                  antenna='5&6'; baseline between antenna index 5 and
                  index 6.
                  antenna='VA05&VA06'; baseline between VLA antenna 5
                        and 6.
                  antenna='5&6;7&8'; baselines 5-6 and 7-8
                  antenna='5'; all baselines with antenna index 5
                  antenna='05'; all baselines with antenna number 05
                 (VLA old name)
                  antenna='5,6,9'; all baselines with antennas 5,6,9
                    index numbers

              timerange  -- Select data based on time range:
                 default = '' (all); examples,
                  timerange = 'YYYY/MM/DD/hh:mm:ss~YYYY/MM/DD/hh:mm:ss'
                  Note: if YYYY/MM/DD is missing date defaults to first
            day in data set
                  timerange='09:14:0~09:54:0' picks 40 min on first day
                  timerange= '25:00:00~27:30:00' picks 1 hr to 3 hr
                 30min on NEXT day
                  timerange='09:44:00' pick data within one integration
                     of time
                  timerange='>10:24:00' data after this time

              scan -- Scan number range.
                  default: '' (all)
                  example: scan='1~5'
                  Check 'go listobs' to insure the scan numbers are in

              array -- Select data by (sub)array indices
                  default: '' (all); example:
                  array='0~2'; arrays 0 to 2

      mode -- Frequency Specification:
               NOTE: See examples below:
               default: 'channel'
                 mode = 'channel'; Use with nchan, start, width to specify
                         output spw. Produces equidistant grid based on first
                         selected channel. See examples below.
                 mode = 'velocity', means channels are specified in
                 mode = 'frequency', means channels are specified in
                 mode = 'channel_b', alternative 'channel' mode.
                 Does not force an equidistant grid. Faster.

  >>> mode expandable parameters
               Start, width are given in units of channels, frequency
           or velocity as indicated by mode
               nchan -- Number of channels in output spw
                 default: -1 = all channels; example: nchan=3
               start -- Start or end input channel (zero-based) depending on the sign of the width parameter
                 default=0; example: start=5
               width -- Output channel width in units of the input
              channel width (sign indicates whether the start parameter is lower(+) or upper(-) end of the range)
                 default=1; example: width=4
               interpolation -- Interpolation method (linear, nearest, cubic, spline, fftshift)
                 default = 'linear'
               spw = '0,1'; mode = 'channel'
                  will produce a single spw containing all channels in spw
                0 and 1
               spw='0:5~28^2'; mode = 'channel'
                  will produce a single spw made with channels
               spw = '0'; mode = 'channel': nchan=3; start=5; width=4
                  will produce an spw with 3 output channels
                  new channel 1 contains data from channels (5+6+7+8)
                  new channel 2 contains data from channels (9+10+11+12)
                  new channel 3 contains data from channels (13+14+15+16)
               spw = '0:0~63^3'; mode='channel'; nchan=21; start = 0;
            width = 1
                  will produce an spw with 21 channels
                  new channel 1 contains data from channel 0
                  new channel 2 contains data from channel 2
                  new channel 21 contains data from channel 61
               spw = '0:0~40^2'; mode = 'channel'; nchan = 3; start =
            5; width = 4
                  will produce an spw with three output channels
                  new channel 1 contains channels (5,7)
                  new channel 2 contains channels (13,15)
                  new channel 3 contains channels (21,23)

      phasecenter -- Direction measure  or fieldid. To be used in mosaics to indicate
               the center direction to be used in the spectral coordinate transformation.
               default: '' => first field selected ; example: phasecenter=6
               or phasecenter='J2000 19h30m00 -40d00m00'

      restfreq -- Specify rest frequency to use for output image
               default='' Occasionally it is necessary to set this (for
               example some VLA spectral line data).  For example for
               NH_3 (1,1) put restfreq='23.694496GHz'

      outframe -- output reference frame (not case-sensitive)
               possible values: LSRK, LSRD, BARY, GALACTO, LGROUP, CMB, GEO, TOPO, or SOURCE
               (SOURCE is meant for solar system work and corresponds to GEO + radial velocity
               correction for ephemeris objects).
               default='' (keep original reference frame) ; example: outframe='BARY'     

      veltype -- definition of velocity (in mode)
               default = 'radio'

      hanning -- if true, Hanning smooth frequency channel data to remove Gibbs ringing