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Version 1.9 Build 1556

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dragon.setimage - Function

	Package	synthesis
	Module	imager
	Tool	dragon

Set the image parameters for subsequent processing

Synopsis
setimage(name, nx, ny, cellx, celly, stokes, doshift, phasecenter, shiftx, shifty, mode, nchan, start, step, spwid, fieldid, facets, name)

Description
Define the default image parameters.

Note that some parameters can be specified either in canonical units or via measures. To establish default values, the ids for the default spectral window and default field id must be given.

The meaning of arguments mode, nchan, step, etc. is described in setdata. dragon can perform multi-frequency synthesis over several spectral windows (mode='mfs'). To acheive this, you should set spwid to an array of the required spectral windows (e.g. spwid=1:2).

The phase center of the image defaults to that of the specified fieldid (the first if none is specified). Note that fieldid refers to the field identifier in the MeasurementSet and is not connected to the number of facets in any way. A phase center may be also specified in an argument to setimage using any valid direction. If the conversion from the observed direction requires frame information then this is taken as follows:

• Direction information, including the coordinate system, is taken from the relevant entry in the Field table of the MeasurementSet.
• The epoch is taken from the time of observation of each visibility.
• A position is specified via the dragon tool function setoptions

If the specified number of facets is greater than unity then the image is split into facets (this number along the x and y axes) and processed.

Finally, a position shift may be added using the arguments shiftx, shifty. This will be added to whatever the phase center was set to as described above. The shift is a real angle on the dragon so that, in e.g. RA, DEC, the RA shift is divided by cos(DEC) before being added to the RA. The sense of the shift is that the position after addition of the shift gives the new phase center of the image. The shift is in the reference frame of the phase center.

Arguments

name		Name of output image
		Allowed:	String
		Default:	dragon
nx		Number of spatial pixels in x
		Allowed:	Int
		Default:	128
ny		Number of spatial pixels in y
		Allowed:	Int
		Default:	128
cellx		Cellsize in x (e.g. '1arcsec')
		Allowed:	Quantity
		Default:	'1arcsec'
celly		Cellsize in y (e.g. '1arcsec')
		Allowed:	Quantity
		Default:	'1arcsec'
stokes		Stokes parameters to image (e.g. 'IQUV')
		Allowed:	'I'|'IV'|'IQU'|'IQUV'
		Default:	'I'
doshift		Use the specified phase center? T or F
		Allowed:	Bool
		Default:	T
phasecenter		Direction of phase center as a measure
		Allowed:	MDirection
shiftx		Shift in x (e.g. '23.7arcsec')
		Allowed:	Quantity
		Default:	'0arcsec'
shifty		Shift in y (e.g. '-54.2arcsec')
		Allowed:	Quantity
		Default:	'0arcsec'
mode		Type of processing
		Allowed:	'mfs'|'channel'|'velocity'
		Default:	'mfs'
nchan		Number of channels
		Allowed:	Int
		Default:	1
start		Start channel (1-relative)
		Allowed:	Int
step		Step in channel
		Allowed:	Int
spwid		Spectral Window Ids (1 relative)
		Allowed:	Vector of Ints
		Default:	1
fieldid		Field Id (1 relative)
		Allowed:	Int
		Default:	1
facets		Number of facets
		Allowed:	Integer
		Default:	1
name		Name of output image
		Allowed:	String
		Default:	dragon