FITS conversion

The task imageToFITS task provides a mechanism for converting a CASA-format image to a FITS file. It allows a lot more flexibility than the casacore image2fits task, providing a front-end to the ImageFITSConverter::ImageToFITS function in casacore. Each of the arguments for this function are exposed via the ParameterSet interface.

The task also allows the user to set image header/metadata values and history statements. These are applied to the CASA image first, and then flow through into the FITS file.

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.

$  imageToFITS -c config.in

The imageToFITS program is not parallel/distributed, it runs in a single process operating on a single input CASA image.

Configuration Parameters

All parameters should be prefaced by ImageToFITS.

Parameter	Type	Default	Description
Metadata
headers	vector<string>	[]	Vector of strings, being metadata header names to add to the image. Each header name is then specified as its own parameter to provide the value.
headers. headerName	string	None	Value for the metadata header headerName
history	vector<string>	[]	Vector of strings to be recorded in the image metadata as HISTORY statements. Each string gets its own HEADER line.
FITS conversion
casaimage	string	None	The input CASA-format image.
fitsimage	string	None	The output FITS-format image.
memoryInMB	int	64	Setting this to zero will result in row-by-row copying, otherwise it will attempt to copy with as large a chunk-size as possible, while fitting in the desired memory.
preferVelocity	bool	false	Write a velocity primary spectral axis if possible.
opticalVelocity	bool	true	If writing a velocity, use the optical definition (otherwise use radio).
bitpix	float	-32	bitpix can presently be set to -32 or 16 only. When bitpix is 16 it will write BSCALE and BZERO into the FITS file. If minPix is greater than maxPix the minimum and maximum pixel values will be determined from the array, otherwise the supplied values will be used and pixels outside that range will be truncated to the minimum and maximum pixel values. Note that this truncation does not occur for bitpix=-32.
minpix	float	1.0	Minimum pixel value for scaling in bitpix=16 case.
maxpix	float	-1.0	Minimum pixel value for scaling in bitpix=16 case.
allowOverwrite	bool	false	If true, allow fitsimage to be overwritten if it already exists.
degenerateLast	bool	false	If true, axes of length 1 will be written last to the header.
stokesLast	bool	false	Put the Stokes axis last in the FITS file.
verbose	bool	true	More log messages.
preferWavelength	bool	false	If true, write a wavelength primary axis.
airWavelength	bool	false	If true and preferWavelength is true write an air wavelength primary axis.
copyHistory	bool	true	Whether to copy the CASA image’s history

Example

# CASA image input
ImageToFITS.casaimage = image.i.cube.linmos.restored
# FITS image output
ImageToFITS.fitsimage = image.i.cube.linmos.restored.fits
# Put the Stokes axis last
ImageToFITS.stokesLast = true
# Ensure the spectral axis stays in frequency, as we are regularly sampled there.
ImageToFITS.preferVelocity = false
# Add some additional headers
ImageToFITS.headers = ["project","sbid","date-obs","duration"]
ImageToFITS.headers.project = AS033
ImageToFITS.headers.sbid = 1531
ImageToFITS.headers.date-obs = 2016-06-29T11:21:15.9
ImageToFITS.headers.duration = 21534.3
# Add some history statements showing provenance
ImageToFITS.history = ["Produced with ASKAPsoft version 0.14.0","Produced using ASKAP pipeline version 0.14.0"]