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 to 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)

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

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.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 three options are used.

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)

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

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

# 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

# Output specific parameters
Cmodel.output             = casa
Cmodel.filename           = image_10uJy.skymodel

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

# 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