2.3.1.0 imager.setoptions

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imager.setoptions - Function

2.3.1 Set some general options for subsequent processing

Description

This function is for setting different gridding and memory options

ftmachine

The options for ftmachine are:

ft: Standard interferometric gridding
sd: Standard single dish gridding
both: ft and sd as appropriate.
wproject: option for using the wproject algorithm for wide-field imaging; when this option is used the parameter wprojplanes define the number of convolution functions to be used
mosaic: option to use the gridder that uses the primary beam as the convolution function in gridding

cache

The size of the cache used (in complex pixels) during the gridding process. The default is to use half the physical memory of the machine as specified by the aipsrc variable system.resources.memory.

tile

The side of the tile (in complex pixels) during the gridding process.

gridfunction

The gridding function used. Currently only Box-car (’BOX’) and Prolate Spheriodal Wave Function (’SF’) are supported. In the case of Single-Dish imaging the Primary Beam (’PB’), Gaussian (’GAUSS’), and Gaussian * Jinc (’GJINC’) also can be used.

location

For some unusual types of image, one needs to know the location to be used in calculating phase rotations. For example, one can specify images to be constructed in azel, in which case, an antenna position must be chosen. One can use functions of measures: either observatory to get the position of a named observatory (e.g. me.observatory(’ATCA’)) or position to set the position (e.g.me.position(’wgs84’,’30deg’,’40deg’,’10m’)). Although this information is available from the MeasurementSet, what location is ambiguous in some cases e.g. VLBI.

padding

When gridding and transforming, the array may be padded by this factor in the image plane. This reduces aliasing, especially in wide-field cleaning.

usemodelcol

if this is false it tells imager to create and use the model visibility on the fly and in memory as far as possible...otherwise if it is True then imager will use the MODEL_DATA column to do this.

wprojplanes

this parameter is is used only of ftmachine is set to wproject. This defines how many convolution functions is used in the Wprojection gridder (a -1 implies an automatic determination).

Arguments


Inputs
ftmachine	Fourier transform machine
	allowed:	string
	Default:	ft
cache	Size of gridding cache in complex pixels; default use half the memory available on computer
	allowed:	int
	Default:	-1
tile	Size of a gridding tile in pixels (in 1 dimension)
	allowed:	int
	Default:	16
gridfunction	Gridding function
	allowed:	string
	Default:	SF
location	Location used in phase rotations
	allowed:	any
	Default:	variant
padding	Padding factor in image plane (>=1.0)
	allowed:	double
	Default:	1.0
freqinterp	interpolation mode in frequency;options:- nearest, linear, cubic, spline
	allowed:	string
	Default:	nearest
wprojplanes	No of gridding convolution functions used in wproject-ft machine (-1 means let the code decide this number)
	allowed:	int
	Default:	-1
epjtablename	E-Jones table name. This is used if applypointingoffsets is set to True.
	allowed:	string
	Default:
applypointingoffsets	Apply pointing offset corrections during deconvolution.
	allowed:	bool
	Default:	false
dopbgriddingcorrections	Correct for PB gridding before prediction of visibilities. This should be True when doing deconvolution. This should be False when predicting visibilities for model sky with no primary beam attenuation in the model.
	allowed:	bool
	Default:	true
cfcachedirname	Directory where convolution functions are to be (or are being ) cached on the disk.
	allowed:	string
	Default:
rotpastep	The PA increment in degree used for on-the-fly (OTF) rotation of the A-term in A-Projection.
	allowed:	double
	Default:	5.0
pastep	The PA increment in degree used to compute the PA-rotated A-term in A-Projection.
	allowed:	double
	Default:	360.0
pblimit	Primary beam limit when using PBWProjection
	allowed:	double
	Default:	0.05
imagetilevol	Tile size on for image on disk (in pixel, multiply by 4 to get the byte size). It is safe to leave this as default, meant for usage on filesystem like Lustre, the default (0) implies 32x32x4x32 tile shape. Setting it explicitly to a negative number will also try to avoid using disk templattices when possible.
	allowed:	int
	Default:	0
singleprecisiononly	Set this value to True to force single precision all the time. Otherwise imager may use double precision gridding (ft and wproject only for now) when it can and deems it fit. Setting to True can be handy on low memory machines
	allowed:	bool
	Default:	false
numthreads	Limit the number of threads used in this run (openmp enabled only)
	allowed:	int
	Default:	-1
psterm	Switch-on the PS-Term?
	allowed:	bool
	Default:	true
aterm	Switch-on the A-Term?
	allowed:	bool
	Default:	true
mterm	Switch-on the M-Term?
	allowed:	bool
	Default:	true
wbawp	Trigger the WB A-Projection algorithm?
	allowed:	bool
	Default:	false
conjbeams	Use frequency conjugate beams in WB A-Projection algorithm?
	allowed:	bool
	Default:	true

Returns
bool

Example

- im.setoptions(cache=10000000, tile=32, gridfunction=’BOX’,
  location=me.location(’vla’))

The above example is to tell imager to use memory to fit 10000000
complex numbers and tile the image with tiles of 32 pixels on a side.
Also it tells imager to use a box function as gridding function.  The
location parameter will make imager overide the position of the
telescope to use (the default is the one it gets from the ms).

im.open(’n1333.ms’)
im.selectvis(fieldid=[2:6, 8:12], spwid=[1:2])
im.defineimage(nx=800, ny=800, cellx=’0.5arcsec’, celly=’0.5arcsec’, mode=’velocity’, nchan=30, mstart=’-10km/s’, mstep=’1.8km/s’, spwid=[1,2],fieldid=3)
im.setoptions(ftmachine=’mosaic’)
im.setvp(dovp=T)
im.setoptions(ftmachine=’mosaic’)
im.clean(algorithm=’mfclark’, model=’try1’, niter=200)

In the above example we are making a mosaic using the fields
2,3,4,5,6,8,9,10,11,12 and we use the mosaic ftmachine. This uses the
primary beam of the telescope as the gridding function.

im.open(’coma.ms’)
im.selectvis(spwid=1, fieldid=1);
mydir=me.direction(’J2000’, ’12h30m48’, ’12d24m0’)
im.defineimage(nx=200, cellx=’30arcsec’, phasecenter=mydir);
im.make(’outlier1’);
im.defineimage(nx=1800, cellx=’30arcsec’);
im.setoptions(ftmachine=’wproject’,wprojplanes=512, padding=1.0)
im.make(’main’)
im.clean(algorithm=’mfclark’,model=[’main’, ’outlier1’], niter=10000, image=[’coma.image’, ’outlier1.image’])
im.done()

In the above example we are using the Wprojection algorithm for 3-D
imaging. We are using 512 gridding functions. Sometimes if there is a
memory issue (very large images and many griding functions) we suggest
the use of facetting of the image with wprojection. So the example
above would be something like below. Note that when using facets only
the {\tt wfclark} and {\tt wfhogbom} can be used for now. Note on how
an outlier field (or flanking) field is set on an interfering  source
outside of the field of interest.

im.open(’coma.ms’)

im.selectvis(spwid=1, fieldid=1);
mydir = me.direction(’J2000’, ’12h30m48’, ’12d24m0’)
im.defineimage(nx=200, ny=200, cellx=’30arcsec’, celly=’30arcsec’, phasecenter=mydir);
im.make(’outlier1’);
im.defineimage(nx=3000, ny=3000, cellx=’30arcsec’,celly=’30arcsec’,facets=3);
im.setoptions(ftmachine=’wproject’,wprojplanes=200, padding=1.2)
im.make(’main’)
im.clean(algorithm=’wfclark’,model=[’main’, ’outlier1’], niter=10000)
im.done()

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