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| − | mosaic simulation task:
| + | {{simdata}} |
| − | mosaic simulation task:
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| − | This task simulates interferometric observations (currently
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| − | only ALMA can be done easily). New functionality is actively
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| − | being added, so if you have changed versions of CASA, check
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| − | the inputs carefully.
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| − | Please contact CASA experts with any questions, especially
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| − | about features noted below as *experimental*
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| − | -------------------------------
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| − | project -- root filename for all output files.
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| − | -------------------------------
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| − | modifymodel -- change the coordinate system of the model sky image?
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| − | * if graphics selected, display the rescaled model image
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| − | skymodel -- if modifymodel=False, use this as the sky model.
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| − | * if modifyimage=True, use this as the starting point, modify it
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| − | write the output to a different image (default $project.skymodel)
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| − | and use that new image as the sky model
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| − | inbright -- peak brightness in Jy/pixel, or "" for unchanged
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| − | * NOTE: "unchanged" will take the numerical values in your image
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| − | and assume they are in Jy/pixel, even if it says some other unit
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| − | in the header.
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| − | indirection -- central direction, or "" for unchanged
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| − | incell -- spatial pixel size, or "" for unchanged
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| − | incenter -- frequency of center channel e.g. "89GHz", or "" for unchanged
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| − | inwidth -- width of channels, or "" for unchanged - this should be a
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| − | string representing a quantity with units e.g. "10MHz"
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| − | * NOTE: only works reliably with frequencies, not velocities
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| − | * NOTE: it is not possible to change the number of spectral planes
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| − | of the sky model, only to relabel them with different frequencies
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| − | That kind of regridding can be accomplished with the CASA toolkit.
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| − | -------------------------------
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| − | setpointings -- calculate a map of pointings, or if false, provide ptgfile
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| − | * if graphics selected, display the pointings shown on the model image
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| − | ptgfile -- a text file specifying directions in the same
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| − | format as the example, and optional integration times, e.g.
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| − | #Epoch RA DEC TIME(optional)
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| − | J2000 23h59m28.10 -019d52m12.35 10.0
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| − | * if the time column is not present in the file, it will use
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| − | "integration" for all pointings.
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| − | * NOTE: at this time the file should contain only science pointings:
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| − | simdata will observe these, then optionally the calibrator,
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| − | then the list of science pointings again, etc, until totaltime
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| − | is used up.
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| − | integration --- Time interval for each integration e.g '10s'
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| − | * NOTE: to simulate a "scan" longer than one integration, use
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| − | setpointings to generate a pointing file, and then edit the
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| − | file to repeat each pointing several times before moving to the
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| − | next point.
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| − | direction -- mosaic center direction e.g 'J2000 19h00m00 -40d00m00'
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| − | * can optionally be a list of pointings
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| − | * otherwise simdata will pack mapsize according to maptype
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| − | mapsize -- angular size of map
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| − | * set to "" to span the model image
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| − | maptype -- hexagonal or linear
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| − | pointingspacing -- spacing in between beams e.g '1arcsec'
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| − | or "0.25PB" to use 1/4 of the primary beam FWHM, or
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| − | "" will use the primary beam HWHM.
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| − | -------------------------------
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| − | predict -- calculate visibilities from skymodel (which may have been
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| − | modified above, (optionally) complist, and $ptgfile (which
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| − | may have been generated above)
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| − | * if graphics selected, display the array (like plotants), the uv
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| − | coverage, the synthesized (dirty) beam, and ephemeris information
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| − | * if simulating from component list only, you should specify
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| − | modifymodel=False, and set compwidth, the desired bandwidth -
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| − | there is not currently a way to specify the spectrum of a component,
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| − | so simulations from a componentlist only will be continuum (1 chan)
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| − | refdate -- central time of simulated observation eg: '2012/05/21/22:05:00'
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| − | * NOTE: observations are currently centered at the nearest transit *
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| − | totaltime --- total time of observation e.g '7200s'
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| − | antennalist -- ascii file containing antenna positions.
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| − | each row has x y z coordinates and antenna diameter;
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| − | header lines are required to specify the observatory name
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| − | and coordinate system e.g.
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| − | # observatory=ALMA
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| − | # coordsys=UTM
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| − | # datum=WGS84
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| − | # zone=19
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| − | * standard arrays are found in your CASA data repository,
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| − | os.getenv("CASAPATH").split()[0]+"/data/alma/simmos/"
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| − | * if "", will not not produce an interferometric MS
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| − | * a string of the form "alma;0.5arcsec" will be parsed into a full 12m ALMA
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| − | configuration. This only works for full ALMA and may fail to find the
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| − | standard configuration files on some systems - see casaguides.nrao.edu
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| − | caldirection -- *NEW* an unresolved calibrator can be observed
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| − | interleaved with the science pointings. This feature is
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| − | experimental, so please contact us with any questions.
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| − | * The calibrator is implemented as a point source clean component
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| − | with this direction and flux=calflux
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| − | sdantlist -- antenna position file with antennas to be used for
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| − | single dish or total power simulation
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| − | * if "", will not produce a total power MS
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| − | sdant -- the index of the antenna in the list to use for total
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| − | power. defaults to the first antenna on the list.
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| − | -------------------------------
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| − | thermalnoise -- add thermal noise
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| − | * this parameter takes two possible values:
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| − | - tsys-atm: J. Pardo's ATM library will be used to construct an
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| − | atmospheric profile for the ALMA site:
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| − | altitude 5000m, ground pressure 650mbar, relhum=20%,
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| − | a water layer of user_pwv at altitude of 2km,
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| − | the sky brightness temperature returned by ATM,
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| − | and internally tabulated receiver temperatures
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| − | - tsys-manual: instead of using the ATM model, specify the zenith
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| − | sky brightness and opacity manually. Noise is added and then
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| − | the visibility flux scale is referenced above the atmosphere.
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| − | * In either mode, noise is calculated using an antenna spillover
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| − | efficiency of 0.96, taper of 0.86,
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| − | surface accuracy of 25 and 300 microns for ALMA and EVLA
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| − | respectively (using the Ruze formula for surface efficiency),
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| − | correlator efficiencies of 0.95 and 0.91 for ALMA and EVLA,
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| − | receiver temperatures for ALMA of
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| − | 17, 30, 37, 51, 65, 83,147,196,175,230 K interpolated between
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| − | 35, 75,110,145,185,230,345,409,675,867 GHz,
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| − | for EVLA of
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| − | 500, 70, 60, 55, 100, 130, 350 K interpolated between
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| − | 0.33,1.47,4.89,8.44,22.5,33.5,43.3 GHz,
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| − | for SMA of
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| − | 67, 116, 134, 500 K interpolated between
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| − | 212.,310.,383.,660. GHz
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| − | * These are only approximate numbers and do not take into account
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| − | performance at edges of receiver bands, neither are they guaranteed
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| − | to reflect the most recent measurements. Caveat emptor and use the
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| − | sm tool to add noise if you want more precise control.
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| − | t_ground -- ground/spillover temperature in K
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| − | user_pwv -- precipitable water vapor if constructing an atmospheric model
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| − | t_sky -- atmospheric temperature in K [for tsys-manual]
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| − | tau0 -- zenith opacity at observing frequency [for tsys-manual]
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| − | * see casaguides.nrao.edu for more information on noise,
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| − | in particular how to add a phase screen using the toolkit
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| − | -------------------------------
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| − | leakage -- add cross polarization corruption of this fractional magnitude
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| − | -------------------------------
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| − | image -- invert and deconvolve the measurement set(s)
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| − | * NOTE: interactive clean or more parameters than the subset visible
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| − | here are available by simply running the clean task directly,
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| − | then returning to simdata to run "analyze" if desired.
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| − | * NOTE: the channelization of the output image cube will be the
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| − | same as that in the simulated Measurement Set.
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| − | * if graphics selected, display the clean image and residual image
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| − | * uses Cotton-Schwab clean for single fields and Mosaic gridding
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| − | for multiple fields (with Clark PSF calculation in minor cycles).
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| − | vis -- the simulated interferometric MS, or total-power one, or both
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| − | ** use $project.noisy.ms if you have corrupted the MS
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| − | modelimage -- prior (e.g. SD) image to be used in clean
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| − | cell -- cell size e.g '10arcsec'. "" defaults to the skymodel cell
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| − | imsize -- image size in spatial pixels (x,y)
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| − | 0 or -1 will use the model image size; example: imsize=[500,500]
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| − | niter -- mumber of clean/deconvolution iterations, 0 for no cleaning
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| − | threshold -- flux level to stop cleaning
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| − | weighting -- weighting to apply to visibilities
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| − | options: 'natural','uniform','briggs' (robust=0.5)
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| − | outertaper -- apply additional uv outer taper of visibilities
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| − | stokes -- Stokes parameters to image; 'I','IV','IQU','IQUV'
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| − | -------------------------------
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| − | analyze -- compute and display difference between model and output,
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| − | fidelity, etc.
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| − | * it is recommended to have graphics turned on for this subtask
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| − | showarray -- like plotants (ignored in single dish simulation)
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| − | showuv -- display uv coverage
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| − | showpsf -- display synthesized (dirty) beam (ignored in single dish simulation)
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| − | showmodel -- display sky model at original resolution
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| − | showconvolved -- display sky model convolved with output beam
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| − | showclean -- display the synthesized image
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| − | showresidual -- display the clean residual image (ignored in single dish simulation)
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| − | showdifference -- display difference between output cleaned image and
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| − | input model sky image convolved with output synthesized beam
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| − | showfidelity -- display fidelity image
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| − | fidelity = input/max( abs(input-output), 0.7*rms(output) )
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| − | -------------------------------
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| − | How to specify a model image:
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| − | -------------------------------
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| − | * simdata requires a CASA or fits image. If you merely have a grid of
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| − | numbers, you will need to write them out as fits or write a CASA script to
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| − | read them in and use the ia tool to create an image and insert the data.
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| − | * simdata does NOT require a coordinate system in the header. If the
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| − | coordinate information is incomplete, missing, or you would like to
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| − | override it, set "modifymodel=True". simdata will then assume that the
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| − | axes of your input correspond to RA, Dec, and (optionally) frequency and
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| − | (optionally) Stokes parameter.
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| − | * If you have a proper Coordinate System, simdata will so its best to
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| − | generate visibilities from that, and then create a synthesis image
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| − | according to the specified user parameters. Regridding the
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| − | spectral dimension may not have complete flexibility yet.
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| − | * You can manipulate an image header with the "imhead" task, or you can
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| − | delve deeper with the ia and cs tools. If you use the tools, you should
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| − | be aware that a CoordinateSystem in CASA can exist independently of an
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| − | Image. Once the CoordinateSystem is detached from the image, it is the
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| − | users responsibility to do any manipulation e.g. axis reordering on
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| − | both. Example:
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| − | ia.open("myimage_filename")
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| − | ia.summary() # see header as attached to the image
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| − | csys=ia.coordsys() # detach the CoordinateSystem
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| − | csys.summary() # examine it
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| − | csys.setreferencepixel([100,100])
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| − | arr=ia.getchunk() # get the data from the Image
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| − | ia.done()
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| − | csys.reorder([0,2,1]) # reorder the CoordinateSystem
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| − | arr=arr.reorder([0,2,1]) # reorder the data
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| − | ia.fromshape(outfile="mynewimage_file",shape=[32,32,256],csys=csys.torecord(),overwrite=True)
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| − | # make a new image, with the right shape and CoordinateSystem
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| − | ia.putchunk(arr) # put the data into the new image.
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| − | csys.done()
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| − | ia.done()
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| − | -------------------------------
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| − | Output produced: (not all will always exist, depending on input parameters)
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| − | -------------------------------
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| − | project.skymodel = 4d input sky model image (optionally) scaled
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| − | project.skymodel.flat.regrid.conv = input sky regridded to match the output
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| − | image, and convolved with the output synthesized beam
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| − | project.skymodel.png = diagnostic figure of sky model with pointings
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| − | project.ptg.txt = list of mosaic pointings
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| − | project.quick.psf = psf calculated from uv coverage
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| − | project.ms = noise-free measurement set
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| − | project.noisy.ms = corrupted measurement set
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| − | project.predict.png = diagnostic figure of uv coverage and visibilities
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| − | project.image = synthesized image
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| − | project.flux.pbcoverage = promary beam correction for mosaic image
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| − | project.residual = residual image after cleaning
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| − | project.clean.last = parameter file of what parameters were used in the
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| − | clean task
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| − | project.psf = synthesized beam calculated from weighted uv distribution
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| − | project.image.png = diagnostic figure of clean image and residual
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| − | project.fidelity = fidelity image
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| − | project.analysis.png = diagnostic figure of difference and fidelity
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| − | project.simdata.last = saved input parameters for simdata task
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