uvmodelfit

uvmodelfit(vis, field='', spw='', selectdata=True, timerange='', uvrange='', antenna='', scan='', msselect='', niter=5, comptype='P', sourcepar=[1.0, 0.0, 0.0], varypar='', outfile='')[source]

Fit a single component source model to the uv data

[Description] [Examples] [Development] [Details]

Parameters

  • vis (path) - Name of input visibility file

  • field (string=’’) - Select field using field id(s) or field name(s)

  • spw (string=’’) - Select spectral window/channels

  • selectdata (bool=True) - Other data selection parameters

    selectdata = True

    • timerange (string=’’) - Select data based on time range

    • uvrange (variant=’’) - Select data within uvrange (default units meters)

    • antenna (string=’’) - Select data based on antenna/baseline

    • scan (string=’’) - Scan number range

    • msselect (string=’’) - Optional complex data selection (ignore for now)

  • niter (int=5) - Number of fitting iterations to execute

  • comptype (string=’P’) - component model type: P(oint), G(aussian), or D(isk)

  • sourcepar (doubleVec=[1.0, 0.0, 0.0]) - Starting guess for component parameters (3 values for type P, 5 for G and D)

  • varypar (boolVec=’’) - Control which parameters to let vary in the fit

  • outfile (string=’’) - Optional output component list table

Description

Warning

There are Known Issues for uvmodelfit.

Fit a single component source model to the uv-data. Three models are available: P=point; G=Gaussian; D=Disk. Fitting parameters can be held fixed. The results are given in the CASA log and placed in a components file. More information can be found about uvmodelfit here .

Note

INFO: The Nordic ALMA Regional Center Node has developed tools for fitting multiple components of any shape to the visibilities. Their versatile uvmultifit [1] package is provided on their software tools page.

Parameter descriptions

vis

Name of input visibility file. Default: none. Examples: vis=’ngc5921.ms’

field

Select data based on field id(s) or name(s). Default: ‘’ (all). Examples: field=’1’; field=’0~2’, field IDs inclusive from 0 to 2; field=’3C*’, all field names starting with 3C

spw

Select data based on spectral window. Default: ‘’ (all). Examples: spw=’1’; spw=’<2’ #spectral windows less than 2; spw=’>1’, spectral windows greater than 1

selectdata

Select a subset of the visibility using MSSelection. Default: False. Examples: selectdata=True

timerange

Select data based on time range. Default = ‘’ (all). Examples: timerange = ‘YYYY/MM/DD/hh:mm:ss~YYYY/MM/DD/hh:mm:ss’

Note

NOTE: YYYY/MM/DD can be dropped as needed.

Further examples:* timerange=’09:14:0~09:54:0’* yields the quoted time range; timerange=’09:44:00’ yields data within one integration of the specified time; timerange=’>10:24:00’ yields data after the specified time; timerange=’09:44:00+00:13:00’ yields data 13 minutes after the specified time

uvrange

Select data within uvrange (default units kilo-lambda). Default: ‘’ (all). Examples: uvrange=’0~1000klambda’, uvrange from 0-1000 kilo-lambda; uvrange=’>4klambda’, uvranges greater than 4 kilo lambda; uvrange=’0~1000km’, uvrange in kilometers

antenna

Select data based on antenna/baseline. Default: ‘’ (all). Examples: antenna=’5&6’, baseline 5-6; antenna=’5&6;7&8’, baselines 5-6 and 7-8; antenna=’5’, all baselines with antenna 5; antenna=’5,6’, all baselines with antennas 5 and 6

scan

Select data based on scan number. Default: ‘’ (all). Examples: scan=’>3’

msselect

Optional data selection (field,spw,time,etc). Default:’’ means select all. Examples: msselect=’FIELD_ID==0’; msselect=’FIELD_ID IN [0,1,2]’ means select fields 0,1 and 2; msselect=’FIELD_ID <= 1’ means select fields 0, 1; msselect=’FIELD_ID==0 && ANTENNA1 IN [0] && ANTENNA2 IN [2:26]’ means select field 0 and antennas 0 to 26, except antenna 1. Other msselect fields are: ‘DATA_DESC_ID’, ‘SPECTRAL_WINDOW_ID’, ‘POLARIZATION_ID’, ‘SCAN_NUMBER’, ‘TIME’, ‘UVW’.

niter

Number of fitting iterations to execute. Default: 5. Examples: niter=20

comptype

Component model type. Default: ‘P’. Options: ‘P’ (point source), ‘G’ (elliptical gaussian), ‘D’ (elliptical disk)

sourcepar

Starting guess for component parameters. Default: [1,0,0] (for comptype=’P’).

If comptype = ‘P’, then sourcepar = [flux,xoff,yoff], where flux = flux (Jy), xoff = offset east (arcsec), yoff = offset north (arcsec).

If comptype = ‘G’ or ‘D’, then sourcepar = [flux,xoff,yoff,majax,axrat,pos], where majax = FWHM along the major axis (arcsec), axrat < 1 is the ratio of minor to major axis, pos = position angle (deg)

varypar

Control which parameters to let vary in the fit. Default: [ ] (all vary). Examples: varypar=[False,True,True]

Examples with comptype, sourcepar, and varypar

Fit a point: comptype = ‘P’, sourcepar = [0.4,0.2,-0.3], varypar = [True,True,True]

Fit a circular Gaussian: comptype = ‘G’, sourcepar = [1.4,0.3,-0.2,0.3, 1, 0], varypar = [ True , True , True , True , False, False]

outfile

Optional output component list table. Default: ‘’. Examples: outfile=’componentlist.cl’

How to get the output values:

cl.open('componentlist.cl')        #open the componentlist 'componentlist.cl'

fit = cl.getcomponent(0)           #stores component informationof the first component

fit                                #to see the list

flux = fit['flux']['value']        #to store the I,Q,U,V, flux

print flux


ra = fit['shape']['direction']['m0']['value']

dec =fit['shape']['direction']['m1']['value']

print ra, dec


bmaj = fit['shape']['majoraxis']['value']     #to get major axis

bmin = fit['shape']['minoraxis']['value']     #to get minor axis

Bibliography

Examples

More information on uvmodelfit can be found here.

# Note: It's best to channel average the data if there are many channels before running a modelfit
split('ngc5921.ms','1445+099_avg.ms', datacolumn='corrected',field='1445*',width='63')

# Initial guess is that it's close to the phase center and has a flux of 2.0 (a priori we know it's 2.47)
uvmodelfit('1445+099_avg.ms', # use averaged data
           niter=5, # Do 5 iterations
           comptype='P', # P=Point source, G=Gaussian, D=Disk
           sourcepar=[2.0,.1,.1], # Source parameters for a point source
           spw='0',
           outfile='gcal.cl') # Output component list file
Development

No additional development details

Parameter Details

Detailed descriptions of each function parameter

vis (path) - Name of input visibility file
field (string='') - Select field using field id(s) or field name(s)
spw (string='') - Select spectral window/channels
selectdata (bool=True) - Other data selection parameters
timerange (string='') - Select data based on time range
uvrange (variant='') - Select data within uvrange (default units meters)
antenna (string='') - Select data based on antenna/baseline
scan (string='') - Scan number range
msselect (string='') - Optional complex data selection (ignore for now)
niter (int=5) - Number of fitting iterations to execute
comptype (string='P') - component model type: P(oint), G(aussian), or D(isk)
sourcepar (doubleVec=[1.0, 0.0, 0.0]) - Starting guess for component parameters (3 values for type P, 5 for G and D)
varypar (boolVec='') - Control which parameters to let vary in the fit
outfile (string='') - Optional output component list table