1.1.1.0 image.tofits

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image.tofits - Function

1.1.1 Convert the image to a FITS file

Description

This function converts the image into a FITS file.

If the image has a rest frequency associated with it, it will always write velocity information into the FITS file. By default the frequency information will be primary as it is the internal native format. If you select velocity=T then by default the velocity is written in the optical convention, but if optical=F it will use the radio convention instead. Alternatively, if you use velocity=F and wavelength=T, the spectral axis will be written in wavelength.

The FITS definition demands equal increment pixels. Therefore, if you write wavelength or optical velocity information as primary, the increment is computed at the spectral reference pixel. If the bandwidth is large, this may incur non-negligible coordinate calculation errors far from the reference pixel if the spectral bins are not originally equidistant in wavelength. Images generated by the CASA clean task have spectral axes which are always equidistant in frequency.

By default the image is written as a floating point FITS file (bitpix= -32). Under rare circumstances you might want to save space and write it as scaled 16 bit integers (bitpix = 16). You can have tofits calculate the scaling factors by using the default minpix and maxpix. If you set minpix and maxpix, values outside of that range will be truncated. This can be useful if all of the FITS images dynamic range is being used by a few high or low values and you are not interested in preserving those values exactly. Besides the factor of two space savings you get by using 16 instead of 32 bits, integer images usually also compress well (for example, with the standard GNU software facility gzip).

If the specified region-of-interest extends beyond the image, it is truncated.

The output mask is the combination (logical OR) of the default input pixel mask (if any) and the OTF mask.

Sometimes it is useful to drop axes of length one (degenerate axes) because not all FITS readers can handle them. Use the dropdeg argument if you want to do this. If you want to specifically only drop a degenerate Stokes axis, use the dropstokes argument.

If you want to place degenerate axes last in the FITS header, use the deglast argument. If you want to make sure that the Stokes axis is placed last in the FITS header, use the stokeslast argument.

Arguments


Inputs
outfile	FITS file name. Default is input name + ’.fits’
	allowed:	string
	Default:
velocity	prefer velocity (rather than frequency) as primary spectral axis?
	allowed:	bool
	Default:	false
optical	use the optical (rather than radio) velocity convention?
	allowed:	bool
	Default:	true
bitpix	Bits per pixel, -32 (floating point) or 16 (integer)
	allowed:	int
	Default:	-32
minpix	Minimum pixel value for BITPIX=16, Default is to autoscale if minpix > maxpix.
	allowed:	double
	Default:	1
maxpix	Maximum pixel value for BITPIX=16, Default is to autoscale if maxpix < minpix.
	allowed:	double
	Default:	-1
region	Region selection. See ”help par.region” for details. Default is to use the full image.
	allowed:	any
	Default:	variant
mask	Mask to use. See help par.mask. Default is none.
	allowed:	any
	Default:	variant
overwrite	Overwrite (unprompted) pre-existing output file?
	allowed:	bool
	Default:	false
dropdeg	Drop degenerate axes?
	allowed:	bool
	Default:	false
deglast	Put degenerate axes last in header?
	allowed:	bool
	Default:	false
dropstokes	Drop Stokes axis?
	allowed:	bool
	Default:	false
stokeslast	Put Stokes axis last in header?
	allowed:	bool
	Default:	true
wavelength	Write spectral axis in units of wavelength (instead of velocity or frequency)?
	allowed:	bool
	Default:	false
airwavelength	When wirting the spectral axis in units of wavelength, use air wavelength instead of vacuum wavelength?
	allowed:	bool
	Default:	false
async	Run asynchronously?
	allowed:	bool
	Default:	false
stretch	Stretch the mask if necessary and possible? See help par.stretch. Default False
	allowed:	bool
	Default:	false
history	Write the image history to the FITS file? Default True
	allowed:	bool
	Default:	true

Returns
bool

Example

"""
#
print "\t----\t tofits Ex 1 \t----"
ia.maketestimage()
ok = ia.tofits(’MYFILE.FITS’,overwrite=true)
# write FITS image file
ok = ia.tofits(’MYFILE2.FITS’, bitpix=16, overwrite=true)
# Write as scaled 16 bit integers
ia.close()
#
"""

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