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casa
$Rev:20696$
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casa
$Rev:20696$
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Functions | |
| def | mosaic |
| def mosaic.mosaic | ( | vis = '', |
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imagename = '', |
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mode = 'mfs', |
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alg = 'clark', |
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imsize = [256, |
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cell = ['1.0arcsec', |
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| arcsec, | |||
phasecenter = '', |
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stokes = 'I', |
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niter = 500, |
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gain = 0.1, |
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threshold = 0.0, |
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mask = [''], |
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cleanbox = [], |
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nchan = 1, |
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start = 0, |
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width = 1, |
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field = '', |
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spw = '', |
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timerange = '', |
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restfreq = '', |
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sdimage = '', |
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modelimage = '', |
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weighting = 'natural', |
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mosweight = False, |
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rmode = 'norm', |
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robust = 0.0, |
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ftmachine = 'mosaic', |
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cyclefactor = 1.5, |
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cyclespeedup = -1, |
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scaletype = 'SAULT', |
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minpb = 0.1, |
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sigma = '0.001Jy', |
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targetflux = '1.0Jy', |
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constrainflux = False, |
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prior = [''], |
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negcomponent = 2, |
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scales = [0, |
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npercycle = 100, |
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npixels = 0, |
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noise = '0.0Jy' |
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| ) |
Create a multi-field deconvolved image with selected algorithm
Two types of point-source deconvolution, as well as multi-scale
deconvolution, are available. A continuum image (mfs) is produced
by gridding together all spectral data. Individual channels or
groups of channels can also be images and then placed in an output
image cube.
The cleaning regions can be specified by an input mask image, from a
file containing rectangular regions, or interactively as the
deconvolution progresses.
The mosaic task only uses the "corrected" datacolumn which is made
from the "data" data column using applycal with the appropriate
calibration tables. Many Stokes combinations are available.
Keyword arguments:
vis -- Name of input visibility file
default: none; example: vis='ngc5921.ms'
imagename -- Pre-name of output images:
default: none; example: imagename='m2'
output images are:
m2.image; cleaned and restored image
m2.flux; relative sky sensitivity over field
m2.model; image of clean components
m2.residual; image of residuals
m2.interactive.mask; image containing clean regions
mode -- Frequency Specification:
NOTE: See examples below:
default: 'mfs'
mode = 'mfs' means produce one image from all specified data.
mode = 'channel'; Use with nchan, start, width to specify
output image cube. See examples below
mode = 'velocity', means channels are specified in velocity.
mode = 'frequency', means channels are specified in frequency.
>>> mode expandable parameters (for modes other than 'mfs')
Start, width are given in units of channels, frequency or velocity
as indicated by mode, but only channel is complete.
nchan -- Number of channels (planes) in output image
default: 1; example: nchan=3
start -- Start input channel (relative-0)
default=0; example: start=5
width -- Output channel width (>1 indicates channel averaging)
default=1; example: width=4
examples:
spw = '0,1'; mode = 'mfs'
will produce one image made from all channels in spw 0 and 1
spw='0:5~28^2'; mode = 'mfs'
will produce one image made with channels (5,7,9,...,25,27)
spw = '0'; mode = 'channel': nchan=3; start=5; width=4
will produce an image with 3 output planes
plane 1 contains data from channels (5+6+7+8)
plane 2 contains data from channels (9+10+11+12)
plane 3 contains data from channels (13+14+15+16)
spw = '0:0~63^3'; mode=chann; nchan=21; start = 0; width = 1
will produce an image with 20 output planes
Plane 1 contains data from channel 0
Plane 2 contains date from channel 2
Plane 21 contains data from channel 61
spw = '0:0~40^2'; mode = 'channel'; nchan = 3; start = 5; width = 4
will produce an image with three output planes
plane 1 contains channels (5,7)
plane 2 contains channels (13,15)
plane 3 contains channels (21,23)
alg -- Algorithm to use (expandable):
default: 'clark': Options: 'clark','hogbom','multiscale','entropy'
'hogbom' Cleans from the images only. Only inner quarter
of image is cleaned
'clark' Cleans from gridded us data. Only inner quarter of
image is cleaned
'multiscale' cleans with several resolutions using hobgom clean
Currently much slower than single resolution. For extended
sources, try single resolution with interactive and
'entropy' Maximum entropy algorithm is still experimental
and not recommended for general use
>>> multiscale expandable parameter
scales -- in pixel numbers; the size of component to deconvolve
default = [0,3,10]
recommended sizes are 0 (point), 3 (points per clean beam), and
10 (about a factor of three lower resolution)
negcomponent' -- Stop component search when the largest
scale has found this number of negative components; -1 means
continue component search even if the largest component is
negative.
default: 2; example: negcomponent=-1
>>> entropy (MEM) expandable parameters (experimental)
sigma -- Target image sigma
default: '0.001Jy'; example: sigma='0.1Jy'
targetflux -- Target flux for final image
default: '1.0Jy'; example: targetflux='200Jy'
constrainflux -- Constrain image to match target flux;
otherwise, targetflux is used to initialize model only.
default: False; example: constrainflux=True
prior -- Name of MEM prior images
default: ['']; example: prior='source_mem.image'
imsize -- Image pixel size (x,y)
default = [256,256]; example: imsize=[350,350]
imsize = 500 is equivalent to [500,500]
cell -- Cell size (x,y)
default= none;
example: cell=['0.5arcsec,'0.5arcsec'] or
cell=['1arcmin', '1arcmin']
cell = '1arcsec' is equivalent to ['1arcsec','1arcsec']
NOTE:cell = '2' makes default cell size of 2 radians!
phasecenter -- direction measure or fieldid for the mosaic center
default: 0 (imply field=0 as center); example: phasecenter=6
or phasecenter='J2000 19h30m00 -40d00m00'
stokes -- Stokes parameters to image
default='I'; example: stokes='IQUV';
Options: 'I','IV''QU','IQUV','RR','LL','XX','YY','RRLL','XXYY'
niter -- Maximum number iterations, set to zero for no CLEANing
default: 500; example: niter=500
gain -- Loop gain for CLEANing
default: 0.1; example: gain=0.5
threshold -- Flux level at which to stop CLEANing (units=mJy)
default: 0.0; example: threshold=0.0
mask -- Name of mask image used for CLEANing
default '' means no mask;
example: mask='orion.mask'.
It is useful to use a mask from a previous interactive mosaic
session for a new execution. The mask image shape
must be the same as the new mosaic.
cleanbox -- Cleaning region:
default: [] defaults to inner quarter of image
Three specification types:
(a) 'interactive' allows the user to build the cleaning
mask interactively using the viewer. The viewer will
appear every npercycle interation, but modify as needed
The final interactive maks is saved in the file
imagename_interactive.mask.
(b) Explicit pixel ranges
example: cleanbox=[110,110,150,145]
clean region with blc=110,100; trc=150,145 (pixel values)
Only one clean region can be given this way.
(c) Filename with pixel values with ascii format:
<fieldindex blc-x blc-y trc-x trc-y> on each line
1 45 66 123 124
2 23 100 300 340
>>> 'interactive' expandable parameter
npercycle -- this is the number of iterations between each clean
to update mask interactively. Set to about niter/5, can also
be changed interactively.
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='<2'; spectral windows less than 2 (i.e. 0,1)
spw='0:5~61'; spw 0, channels 5 to 61
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
timerange -- Time range:
default = '' (all); examples,
selectime = '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' data within one integration of time
timerange='>10:24:00' data after this time
restfreq -- Specify rest frequency to use for 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'
sdimage -- Input Single Dish image to use for model
default='' (no image); example: sdimage='n4826_12mchan.im'
modelimage -- Name of output(/input) model image
default='' (none=imagename.model); modelimage='orion.model'
Note: This specifies the output model if a single dish
image is input or the output model name from the imaging
weighting -- Weighting to apply to visibilities:
default='natural'; example: weighting='uniform';
Options: 'natural','uniform','briggs','radial', 'superuniform'
>>> Weighting expandable parameters
For weighting='briggs'
rmode -- Robustness mode (see help mosaic)
default='norm'; example='abs';
Options: 'norm','abs','none'
robust -- Brigg's robustness parameter
default=0.0; example: robust=0.5;
Options: -2.0 to 2.0; -2 (uniform)/+2 (natural)
noise -- noise parameter to use for rmode='abs' in
briggs weighting
example noise='1.0mJy'
For superuniform/briggs weighting
npixels -- number of pixels to determine uv-cell size
for weight calculation
example npixels=7
mosweight -- Individually weight the fields of the mosaic
default: False; example: mosweight=True
This can be useful if some of your fields are more
sensitive than others (i.e. due to time spent on-source);
this parameter will give more weight to higher sensitivity
fields in the overlap regions.
ftmachine -- Gridding method for the image;
Options: ft (standard interferometric gridding), sd
(standard single dish) both (ft and sd as appropriate),
mosaic (gridding use PB as convolution function)
default: 'mosaic'; example: ftmachine='ft'
cyclefactor -- Change the threshold at which the deconvolution cycle will
stop, degrid and subtract from the visibilities. For poor PSFs,
reconcile often (cyclefactor=4 or 5); For good PSFs, use
cyclefactor 1.5 to 2.0.
default: 1.5; example: cyclefactor=4
cycle threshold = cyclefactor * max sidelobe * max residual
cyclespeedup -- Cycle threshold doubles in this number of iterations
default: -1; example: cyclespeedup=500
scaletype -- Controls scaling of pixels in the image plane.
default='SAULT'; example: scaletype='PBCOR'
Options: 'PBCOR','SAULT'
'SAULT' scale makes an output image where the noise is constant
across the whole mosaic. However, the image is NOT
corrected for the PB pattern, and therefore is not "flux
correct". Division of the SAULT image_name.image image
by the image_name.flux image will produce a "flux correct image".
The 'PBCOR' option uses the SAULT scaling scheme for
deconvolution, but when interactively cleaning shows the
primary beam corrected image; the final PBCOR image is "flux
correct"
minpb -- Minimum PB level to use
default=0.1; example: minpb=0.01
async -- Run asynchronously
default = False; do not run asychronouslyDefinition at line 13 of file mosaic.py.
References task_mosaic.mosaic(), publish_summary.quantity, and vla_uvfits_line_sf.verify.
1.8.0