fixvis
- fixvis(vis, outputvis='', field='""', refcode='', reuse=True, phasecenter='', distances='""', datacolumn='all')[source]
Recalculates (u, v, w) and/or changes Phase Center
[Description] [Examples] [Development] [Details]
- Parameters
vis (path) - Name of input visibility file
outputvis (string=’’) - Name of output visibility file
field (variant=’””’) - Select field using field id(s) or field name(s)
refcode (string=’’) - reference frame to convert UVW coordinates to
reuse (bool=True) - base UVW calculation on the old values?
phasecenter (string=’’) - use this direction as phase center
distances (variant=’””’) - (experimental) List of the distances (as quanta) of the fields selected by field.
datacolumn (string=’all’) - when applying a phase center shift, modify visibilities only in this/these column(s)
Description
Warning
ALERT: fixvis is deprecated in CASA 6.3. Please use task phaseshift instead.
Warning
There are Known Issues for fixvis.
fixvis recalculates (u, v, w) in an MS based on antenna positions, time and source position. fixvis can also change the phase center of visibilities.
If the phase center is changed, the corresponding modifications are applied to the visibility columns given by the parameter datacolumn which is by default set to all (DATA, CORRECTED, and MODEL).
Warning
ALERT: fixvis uses the small angle approximation and may be incorrect for large phase shifts. This may result in sources shifting position if large phase shifts are being applied (shifts up to a few beam sizes have been reported). Please use tclean for phase center shifts during imaging when applicable.
See also the description in section UV Manipulation.
Parameter descriptions
vis
Name of the input visibility MS.
outputvis
Name of the output MS. Default: same as vis
field
The field selection string. Default: ‘’ = all.
refcode
The UVW coordinates are calculated based on a celestial position, the phase direction of the given field. This direction has a reference frame. If that frame is not the desired one, one can use the parameter refcode to convert to a different frame when the UVW coordinates are recalculated. Default: the refcode of PHASE_DIR in the FIELD table. Example: refcode=’B1950’
reuse
If True and the given refcode is different from the original, the present UVW coordinates are just rotated to the new refcode. If False, the coordinates are re-calculated from the phase direction. Default: True; The parameter is ignored when the parameter phasecenter is set.
phasecenter
If set to a valid direction: change the phase center for the given field to this value. Example: phasecenter=’J2000 9h25m00s -05d12m00s’. If given without the equinox, e.g. ‘0h01m00s +00d12m00s’, the parameter is interpreted as a pair of offsets in RA and DEC to the present phase center.
Note
NOTE: The RA offset can be given in units of time or angle. If given as a time (i.e. as a single number with a time unit as in, e.g., 12s or in the XXhXXmXXs or XX:XX:XX.XXX formats), it is applied as is. If given as an angle (e.g., 0.01deg), it is divided by the cos(DEC) before it is applied.
distances
(experimental) List of the distances (as quanta) of the fields selected by field to be used for refocusing. If empty, the distances of all fields are assumed to be infinity. If not a list but just a single value is given, this is applied to all fields. Default: [ ]. Examples: distances=[‘2E6km’, ‘3E6km’], distances=’15au’
datacolumn
When applying a phase center shift, modify visibilities only in this/these column(s). Default: ‘all’ (DATA, CORRECTED, and MODEL). Example: ‘DATA,CORRECTED’ (will not modify MODEL).
- Examples
Example 1:
Recalculate the UVW coordinates for all fields based on the existing phase center information in the FIELD table.
fixvis(vis='NGC3256.ms',outputvis='NGC3256-fixed.ms')
Example 2:
Set the phase center for field ‘Moon’ to the given direction and recalculate the UVW coordinates.
fixvis(vis='Moon.ms',outputvis='Moon-fixed.ms',field='Moon', phasecenter='J2000 9h25m00s 05d12m00s')
- Development
No additional development details
- Parameter Details
Detailed descriptions of each function parameter
vis (path)- Name of input visibility fileDefault: noneExample: vis=’ngc5921.ms’outputvis (string='')- Name of output visibility fileDefault: ‘’ (same as vis)Example: outputvis=’ngc5921_out.ms’field (variant='""')- Select field using field id(s) or field name(s)Default: ‘’ (all fields)Use ‘go listobs’ to obtain the list id’s ornames. If field string is a non-negative integer,it is assumed a field index, otherwise, it isassumed a field name.Examples:field=’0~2’; field ids 0,1,2field=’0,4,5~7’; field ids 0,4,5,6,7field=’3C286,3C295’; field named 3C286 and3C295field = ‘3,4C*’; field id 3, all namesstarting with 4Crefcode (string='')- Reference frame to convert UVW coordinates toDefault: ‘’ (refcode of PHASE_DIR in the FIELDtable)Example: refcode=’B1950’reuse (bool=True)- Base UVW calculation on the old values?Default: TrueOptions: True|FalseNote: ignored if parameter ‘phasecenter’ is setphasecenter (string='')- If set to a valid direction: change the phase center forthe given field to this valueIf given without the equinox, e.g. ‘0h01m00s+00d12m00s’, the parameter is interpreted as apair of offsets in RA and DEC to the presentphasecenter.Example: phasecenter=’J2000 9h25m00s-05d12m00s’Note: The RA offset can be given in units of timeor angle. If given as a time (i.e. as a singlenumber with a time unit as in, e.g., 12s or inthe XXhXXmXXs or XX:XX:XX.XXX formats), it isapplied as is. If given as an angle (e.g.,0.01deg), it is divided by the cos(DEC) before itis applied.distances (variant='""')- (experimental) List of the distances (as quanta) of thefields selected by field.Default: [] (the distances of all fields areassumed to be infinity.)If not a list but just a single value is given,this is applied to all fields.Examples:distances=[‘2E6km’, ‘3E6km’]distances=’15au’datacolumn (string='all')- when applying a phase center shift, modify visibilitiesonly in this/these column(s)Default: ‘all’ (DATA, CORRECTED, and MODEL)Example: datacolumn=’DATA,CORRECTED’ (will notmodify MODEL)