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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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