cmodel

Model Image Generator

The cmodel pipeline task is responsible for extracting a local sky model (LSM) from the global sky model (GSM) and building an image from the components and/or images resulting from the request.

The cmodel program only supports the construction of continuum (i.e. single-channel) images, however it does support taylor terms allowing the modeling of spectral index and curvature.

Running the program

It can be run with the following command, where “config.in” is a file containing the configuration parameters described in the next section.

$ <MPI wrapper> cmodel -c config.in

Parallel/Distributed Execution

The program is distributed and used a master/worker pattern to distribute and manage work. Each worker receives a subset of the components to image. Components are allocated to the workers in small batches, and only when the worker is finished with one batch is another batch allocated to it. This provides a reasonable approach to load-balancing. Once all components have been imaged the images are reduced back to the master and a single image file is written to disk.

The program requires at least two processes to execute, and failure to either execute cmodel as an MPI process or specifying only one MPI process will result in the following error:

Execution requires at least 2 MPI processes (thrown in apps/cmodel.cc:66)

The program also requires at least one of the parameters filename and components.outfile to be present in the configuration. Failure to specify one of these parameters will result in the following error:

FATAL - Running cmodel with neither filename nor components.outfile parameters defined
FATAL - cmodel requires at least one of these parameters defined

If the filename parameter is not defined, no imaging will be done. The value of the components.outfile parameter is used to create a file to store the components. Therefore, if it is not present in the configuration, no components are written to a file.

On the Cray XC30 platform executing with the MPI wrapper takes the form:

$ aprun -n 40 -N 20 cmodel -c config.in

The -n and -N parameters to the aprun application launcher specify 40 MPI processes will be used (39 workers and one master) and each node will host 20 MPI processes. This job then requires two compute nodes.

Configuration Parameters

To apply the primary-beam attentuation to the components from either the sky model service or the catalogue file (e.g. Cmodel.gsm.database = votable), use the primarybeam parameter (see example below).

Parameter	Default	Example	Description
Cmodel.gsm.database	None	dataservice	Either “dataservice”, “votable” or “asciitable”.See below for additional related options
Cmodel.gsm.ref_freq	None	1.4GHz	The reference frequency for the base flux quantity stored in the GSM. Note: Eventually this will just be obtained from the Sky Model Service.
Cmodel.bunit	None	Jy/pixel	Brightness unit
Cmodel.frequency	None	1.420GHz	Reference frequency for the spectral coordinate system.
Cmodel.increment	None	304MHz	Channel increment for the spectral coordinate system (the example shows an image covering 304MHz with 1 channel).
Cmodel.flux_limit	None	10uJy	Lower limit on flux. Only sources of equal of greater flux will be imaged.
Cmodel.shape	None	[5120, 5120]	Output image dimensions
Cmodel.cellsize	None	[5arcsec, 5arcsec]	Cell size (angular size for each pixel)
Cmodel.direction	None	[12h30m00.00, -45.00.00.00, J2000]	Image center. Must be J2000
Cmodel.stokes	[I]	[I,Q,U,V]	Stokes parameters in the output image.
Cmodel.output	casa	casa	Currently only support casa output
Cmodel.filename	None	image_10uJy.skymodel	Name of image file created
Cmodel.prefix	“”	Ccalibrator.	Prefix for parset format source model output
Cmodel.batchsize	100	100	Number of components to send worker when worker requests more work.
Cmodel.nterms	1	1	Number of taylor term images to produce. Valid inputs are 1, 2 and 3.
Cmodel.nearest	true	false	Use nearest neighbour pixel interpolation for point sources if true or Lanczos5 if false. Lanczos5 gives a more accurate uv model but spreads out a point source between pixels over 10x10 pixels with a sinc-like pattern.

If Cmodel.gsm.database is set to dataservice then the Sky Model Data Service is used as the global sky model source. In this case the following options are available.

Parameter	Default	Example	Description
Cmodel.gsm.locator_host	None	localhost	Host or IP address of the ICE locator service
Cmodel.gsm.locator_port	None	4061	IP port the ICE locator service is listening on
Cmodel.gsm.service_name	None	SkyModelService	Identity of the sky model service in the ICE locator service (registry)
Cmodel.dcoffset	0	0	Use this offset if it is greater than the primary beam taper factor
Cmodel.sources.names	None	[my_source]	Name for all the sources. It should be a vector of one element. For example, [my_source1,my_source2] is not allowed.
Cmodel.components.outfile	parset-comp.in	components-parset	Name of the file. For the format of the file, see the sources.definition parameter in the csimulator.
Cmodel.forceSpectralProperty	None	true	The value of this parameter must be set to true otherwise using the cmodel task with the skymodel service does not run.
Cmodel.userDefinedSpectralCurvature	0.0	0.0	User defined spectral curvature value
Cmodel.userDefinedSpectralIndex	0.0	-0.7	User defined spectral index value
Cmodel.extractFromAnnulus	false	true	A flag used to tell cmodel task to get a list of bright sources within a specified annulus
Cmodel.Radii	None	[7.1,7.5]	The value of inner and outer radius in degrees. Note: These values are only used if the extractFromAnnulus is true
Cmodel.primarybeam	None	GaussianPB	Apply the primary-beam attenuation to the components in the sky model service.

If Cmodel.gsm.database is set to votable then a VOTable is used as the global sky model source. In this case the following option is used to specify the name of the file to read in.

Parameter	Default	Example	Description
Cmodel.gsm.file	None	inputfile.xml	File to read

If Cmodel.gsm.database is set to asciitable then a row/column (space separated) file is used as the global sky model source. In this case the following option is used to specify the name of the file to read in.

Parameter	Default	Example	Description
Cmodel.tablespec.ra.col	None	3	Column (zero based) containing the RA
Cmodel.tablespec.ra.units	None	deg	RA units (Must confirm to degrees)
Cmodel.tablespec.dec.col	None	4	Column (zero based) containing the Declination
Cmodel.tablespec.dec.units	None	deg	Declination units (Must confirm to degrees)
Cmodel.tablespec.flux.col	None	10	Column (zero based) containing the flux
Cmodel.tablespec.flux.units	None	Jy	Flux units (Must conform to Jy)
Cmodel.tablespec.majoraxis.col	None	6	Column (zero based) containing the major axis
Cmodel.tablespec.majoraxis.units	None	arcsec	Major axis units (must confirm to degrees)
Cmodel.tablespec.minoraxis.col	None	7	Column (zero based) containing the minor axis
Cmodel.tablespec.minoraxis.units	None	arcsec	Major axis units (must conform to degrees)
Cmodel.tablespec.posangle.col	None	5	Column (zero based) containing the position angle
Cmodel.tablespec.posangle.units	None	rad	Position angle units (must confirm to degrees)
Cmodel.tablespec.spectralindex.col	None	12	Column (zero based) containing the spectral index
Cmodel.tablespec.spectralcurvature.col	None	13	Column (zero based) containing the spectral curvature
Cmodel.primarybeam	None	GaussianPB	Apply the primary-beam attenuation to the components in the catalogue.

Note: Neither spectral index or curvature require units.

Configuration Example

Example 1

This first example demonstrates configuration using the Sky Model Data Service as the global sky model source.

# The below specifies the GSM source is the Sky Model Service
Cmodel.gsm.database       = dataservice
Cmodel.gsm.locator_host   = localhost
Cmodel.gsm.locator_port   = 4061
Cmodel.gsm.service_name   = SkyModelService
Cmodel.gsm.ref_freq       = 1.4GHz

# primary beam attentuation
Cmodel.primarybeam        = GaussianPB

# General parameters
Cmodel.bunit              = Jy/pixel
Cmodel.frequency          = 1.420GHz
Cmodel.increment          = 304MHz
Cmodel.flux_limit         = 10uJy
Cmodel.shape              = [5120, 5120]
Cmodel.cellsize           = [5arcsec, 5arcsec]
Cmodel.direction          = [12h30m00.00, -45.00.00.00, J2000]
Cmodel.stokes             = [I]
Cmodel.nterms             = 3

# must be true otherwise cmodel wont run
Cmodel.forceSpectralProperty        = true
# default for these are 0
Cmodel.userDefinedSpectralIndex = -0.7
Cmodel.userDefinedSpectralCurvature = 0.0

# Get the bright sources within a specified annulus.
# Default is false
# Cmodel.extractFromAnnulus = true
# Only used if extractFromAnnulus is true. Inner and
# outer radii are in degrees.
# Cmodel.Radii = [7.1,7.5]

# Output specific parameters
Cmodel.output             = casa
Cmodel.filename           = image_10uJy.skymodel
# sources output file. Default is parset-comp.in
# Cmodel.components.outfile = filename

Example 2

This second example demonstrates configuration using an output file from the VOTable source finder as the global sky model source.

# The below specifies the GSM source is a duchamp output file
Cmodel.gsm.database       = votable
Cmodel.gsm.file           = duchamp-fitResults.xml
Cmodel.gsm.ref_freq       = 1.421GHz

# primary beam attentuation
Cmodel.primarybeam        = GaussianPB

# General parameters
Cmodel.bunit              = Jy/pixel
Cmodel.frequency          = 1.420GHz
Cmodel.increment          = 304MHz
Cmodel.flux_limit         = 10mJy
Cmodel.shape              = [4096, 4096]
Cmodel.cellsize           = [5arcsec, 5arcsec]
Cmodel.direction          = [12h30m00.00, -45.00.00.00, J2000]
Cmodel.stokes             = [I]
Cmodel.nterms             = 3

# Output specific parameters
Cmodel.output             = casa
Cmodel.filename           = image_10mJy.skymodel