Source code for casatasks.manipulation.fixvis

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[docs]def fixvis(vis, outputvis='', field='""', refcode='', reuse=True, phasecenter='', distances='""', datacolumn='all'): r""" Recalculates (u, v, w) and/or changes Phase Center [`Description`_] [`Examples`_] [`Development`_] [`Details`_] Parameters - vis_ (string) - 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: Description **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 <../../notebooks/uv_manipulation.ipynb#Recalculate-UVW-Values>`__. .. rubric:: 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. .. rubric:: *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'* .. rubric:: *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: 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: Development No additional development details .. _Details: Parameter Details Detailed descriptions of each function parameter .. _vis: | ``vis (string)`` - Name of input visibility file | Default: none | Example: vis='ngc5921.ms' .. _outputvis: | ``outputvis (string='')`` - Name of output visibility file | Default: '' (same as vis) | Example: outputvis='ngc5921_out.ms' .. _field: | ``field (variant='""')`` - Select field using field id(s) or field name(s) | Default: '' (all fields) | | Use 'go listobs' to obtain the list id's or | names. If field string is a non-negative integer, | it is assumed a field index, otherwise, it is | assumed a field name. | Examples: | 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 .. _refcode: | ``refcode (string='')`` - Reference frame to convert UVW coordinates to | Default: '' (refcode of PHASE_DIR in the FIELD | table) | Example: refcode='B1950' .. _reuse: | ``reuse (bool=True)`` - Base UVW calculation on the old values? | Default: True | Options: True|False | Note: ignored if parameter 'phasecenter' is set .. _phasecenter: | ``phasecenter (string='')`` - If set to a valid direction: change the phase center for | the given field to this value | 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 | phasecenter. | Example: phasecenter='J2000 9h25m00s | -05d12m00s' | 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: | ``distances (variant='""')`` - (experimental) List of the distances (as quanta) of the | fields selected by field. | Default: [] (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. | Examples: | distances=['2E6km', '3E6km'] | distances='15au' .. _datacolumn: | ``datacolumn (string='all')`` - when applying a phase center shift, modify visibilities | only in this/these column(s) | Default: 'all' (DATA, CORRECTED, and MODEL) | Example: datacolumn='DATA,CORRECTED' (will not | modify MODEL) """ pass