Cvel
From CASA Guides
Help on cvel task:
regrid an MS to a new spectral window / channel structure or frame
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:
field='NGC5921'
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
0-10,15-60
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
order.
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
velocity.
mode = 'frequency', means channels are specified in
frequency.
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 input channel (relative-0)
default=0; example: start=5
width -- Output channel width in units of the input
channel width (>1 indicates channel averaging)
default=1; example: width=4
interpolation -- Interpolation method
default = 'linear'
examples:
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
(5,7,9,...,25,27)
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;
0 and 1
spw='0:5~28^2'; mode = 'channel'
will produce a single spw made with channels
(5,7,9,...,25,27)
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 for the mosaic center
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
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
