casa::WProjectFT Class Reference

An FTMachine for Gridded Fourier transforms. More...

#include <WProjectFT.h>

Inheritance diagram for casa::WProjectFT:

Public Member Functions
	WProjectFT (Int nFacets, Long cachesize, Int tilesize=16, Bool usezero=True, Bool useDoublePrec=False, const Double minW=-1.0, const Double maxW=-1.0, const Double rmsW=-1.0)
	Constructor: cachesize is the size of the cache in words (e.g.
	WProjectFT (Int nFacets, MPosition mLocation, Long cachesize, Int tilesize=16, Bool usezero=True, Float padding=1.0, Bool useDoublePrec=False, const Double minW=-1.0, const Double maxW=-1.0, const Double rmsW=-1.0)
	Constructor without tangent direction.
	WProjectFT (Int nFacets, MDirection mTangent, MPosition mLocation, Long cachesize, Int tilesize=16, Bool usezero=True, Float padding=1.0, Bool useDoublePrec=False, const Double minW=-1.0, const Double maxW=-1.0, const Double rmsW=-1.0)
	Deprecated no longer need ms in constructor.
	WProjectFT (const RecordInterface &stateRec)
	Construct from a Record containing the WProjectFT state.
	WProjectFT (const WProjectFT &other)
	Copy constructor.
WProjectFT &	operator= (const WProjectFT &other)
	Assignment operator.
	~WProjectFT ()
virtual FTMachine *	cloneFTM ()
	clone to FTMachine pointer
void	initializeToVis (ImageInterface< Complex > &image, const VisBuffer &vb)
	Initialize transform to Visibility plane using the image as a template.
void	finalizeToVis ()
	This version returns the gridded vis...should be used in conjunction.
void	initializeToSky (ImageInterface< Complex > &image, Matrix< Float > &weight, const VisBuffer &vb)
	Initialize transform to Sky plane: initializes the image.
void	finalizeToSky ()
	Finalize transform to Sky plane: flushes the image cache and shows statistics if it is being used.
void	get (VisBuffer &vb, Int row=-1)
	Get actual coherence from grid by degridding.
void	put (const VisBuffer &vb, Int row=-1, Bool dopsf=False, FTMachine::Type type=FTMachine::OBSERVED)
	Put coherence to grid by gridding.
void	makeImage (FTMachine::Type type, VisSet &vs, ImageInterface< Complex > &image, Matrix< Float > &weight)
	Make the entire image.
ImageInterface< Complex > &	getImage (Matrix< Float > &, Bool normalize=True)
	Get the final image: do the Fourier transform and grid-correct, then optionally normalize by the summed weights.
virtual void	normalizeImage (Lattice< Complex > &, const Matrix< Double > &, Lattice< Float > &, Bool)
void	getWeightImage (ImageInterface< Float > &, Matrix< Float > &)
	Get the final weights image.
Bool	toRecord (String &error, RecordInterface &outRec, Bool withImage=False, const String diskimage="")
	Save and restore the WProjectFT to and from a record.
Bool	fromRecord (String &error, const RecordInterface &inRec)
Bool	isFourier ()
	Can this FTMachine be represented by Fourier convolutions?
String	name () const
	Return name of this machine.
void	setConvFunc (CountedPtr< WPConvFunc > &pbconvFunc)
	Copy convolution function etc to another FT machine necessary if ft and ift are distinct but can share convfunctions.
CountedPtr< WPConvFunc > &	getConvFunc ()
virtual void	setMiscInfo (const Int qualifier)
	set the order of the Taylor term for MFS this is to tell A-Projection to qualify the accumulated avgPB for each Taylor term in the CFCache.
virtual void	ComputeResiduals (VisBuffer &, Bool)
	Make the VB and VBStore interefaces for the interim re-factoring work.
Static Public Member Functions
static void	wStat (ROVisibilityIterator &vi, Double &minW, Double &maxW, Double &rmsW)
	Helper function to calculate min, max, rms of W in the data set.
Protected Member Functions
Int	nint (Double val)
void	findConvFunction (const ImageInterface< Complex > &image, const VisBuffer &vb)
	Find the convolution function.
Array< Complex > *	getDataPointer (const IPosition &, Bool)
	Get the appropriate data pointer.
void	ok ()
void	init ()
void	prepGridForDegrid ()
void	findGridSector (const Int &nxp, const Int &nyp, const Int &ixsub, const Int &iysub, const Int &minx, const Int &miny, const Int &icounter, Int &x0, Int &y0, Int &nxsub, Int &nysub, const Bool linear)
	Is this record on Grid? check both ends.
Int	getIndex (const ROMSPointingColumns &mspc, const Double &time, const Double &interval)
Protected Attributes
Float	padding_p
	Padding in FFT.
Int	nWPlanes_p
LatticeCache< Complex > *	imageCache
	Image cache.
Long	cachesize
	Sizes.
Int	tilesize
ConvolveGridder< Double, Complex > *	gridder
	Gridder.
Bool	isTiled
	Is this tiled?
CountedPtr< Lattice< Complex > >	arrayLattice
	Array lattice.
CountedPtr< Lattice< Complex > >	lattice
	Lattice.
Float	maxAbsData
IPosition	centerLoc
	Useful IPositions.
IPosition	offsetLoc
Vector< Double >	uvScale
	Image Scaling and offset.
Vector< Double >	uvOffset
Double	savedWScale_p
Bool	usezero_p
	Grid/degrid zero spacing points?
Cube< Complex >	convFunc
Int	convSampling
Int	convSize
Vector< Int >	convSupport
Vector< Int >	convSizes_p
Int	wConvSize
Int	lastIndex_p
String	machineName_p
CountedPtr< WPConvFunc >	wpConvFunc_p
Double	timemass_p
Double	timegrid_p
Double	timedegrid_p
Double	minW_p
Double	maxW_p
Double	rmsW_p

Detailed Description

An FTMachine for Gridded Fourier transforms.

Intended use:

Public interface

Prerequisite

FTMachine module
SkyEquation module
VisBuffer module

Etymology

FTMachine is a Machine for Fourier Transforms. WProjectFT does Grid-based Fourier transforms.

Synopsis

The SkyEquation needs to be able to perform Fourier transforms on visibility data. WProjectFT allows efficient Fourier Transform processing using a VisBuffer which encapsulates a chunk of visibility (typically all baselines for one time) together with all the information needed for processing (e.g. UVW coordinates).

Gridding and degridding in WProjectFT are performed using a novel sort-less algorithm. In this approach, the gridded plane is divided into small patches, a cache of which is maintained in memory using a general-purpose LatticeCache class. As the (time-sorted) visibility data move around slowly in the Fourier plane, patches are swapped in and out as necessary. Thus, optimally, one would keep at least one patch per baseline.

A grid cache is defined on construction. If the gridded uv plane is smaller than this, it is kept entirely in memory and all gridding and degridding is done entirely in memory. Otherwise a cache of tiles is kept an paged in and out as necessary. Optimally the cache should be big enough to hold all polarizations and frequencies for all baselines. The paging rate will then be small. As the cache size is reduced below this critical value, paging increases. The algorithm will work for only one patch but it will be very slow!

This scheme works well for arrays having a moderate number of antennas since the saving in space goes as the ratio of baselines to image size. For the ATCA, VLBA and WSRT, this ratio is quite favorable. For the VLA, one requires images of greater than about 200 pixels on a side to make it worthwhile.

The FFT step is done plane by plane for images having less than 1024 * 1024 pixels on each plane, and line by line otherwise.

The gridding and degridding steps are implemented in Fortran for speed. In gridding, the visibilities are added onto the grid points in the neighborhood using a weighting function. In degridding, the value is derived by a weight summ of the same points, using the same weighting function.

Example

See the example for SkyModel .

Motivation

Define an interface to allow efficient processing of chunks of visibility data

Definition at line 131 of file WProjectFT.h.

Constructor & Destructor Documentation

casa::WProjectFT::WProjectFT	(	Int	nFacets,
		Long	cachesize,
		Int	tilesize = `16`,
		Bool	usezero = `True`,
		Bool	useDoublePrec = `False`,
		const Double	minW = `-1.0`,
		const Double	maxW = `-1.0`,
		const Double	rmsW = `-1.0`
	)

Constructor: cachesize is the size of the cache in words (e.g.

a few million is a good number), tilesize is the size of the tile used in gridding (cannot be less than 12, 16 works in most cases).

casa::WProjectFT::WProjectFT	(	Int	nFacets,
		MPosition	mLocation,
		Long	cachesize,
		Int	tilesize = `16`,
		Bool	usezero = `True`,
		Float	padding = `1.0`,
		Bool	useDoublePrec = `False`,
		const Double	minW = `-1.0`,
		const Double	maxW = `-1.0`,
		const Double	rmsW = `-1.0`
	)

Constructor without tangent direction.

casa::WProjectFT::WProjectFT	(	Int	nFacets,
		MDirection	mTangent,
		MPosition	mLocation,
		Long	cachesize,
		Int	tilesize = `16`,
		Bool	usezero = `True`,
		Float	padding = `1.0`,
		Bool	useDoublePrec = `False`,
		const Double	minW = `-1.0`,
		const Double	maxW = `-1.0`,
		const Double	rmsW = `-1.0`
	)

Deprecated no longer need ms in constructor.

casa::WProjectFT::WProjectFT ( const RecordInterface & stateRec )

Construct from a Record containing the WProjectFT state.

casa::WProjectFT::WProjectFT ( const WProjectFT & other )

Copy constructor.

casa::WProjectFT::~WProjectFT ( )

Member Function Documentation

virtual FTMachine* casa::WProjectFT::cloneFTM ( ) [virtual]

clone to FTMachine pointer

Reimplemented from casa::FTMachine.

virtual void casa::WProjectFT::ComputeResiduals	(	VisBuffer &	vb,
		Bool	useCorrected
	)			`[inline, virtual]`

Make the VB and VBStore interefaces for the interim re-factoring work.

Finally removed the VB interface.

Implements casa::FTMachine.

Definition at line 230 of file WProjectFT.h.

void casa::WProjectFT::finalizeToSky ( ) [virtual]

Finalize transform to Sky plane: flushes the image cache and shows statistics if it is being used.

DOES NOT DO THE FINAL TRANSFORM!

Implements casa::FTMachine.

void casa::WProjectFT::finalizeToVis ( ) [virtual]

This version returns the gridded vis...should be used in conjunction.

Finalize transform to Visibility plane: flushes the image cache and shows statistics if it is being used.

Implements casa::FTMachine.

void casa::WProjectFT::findConvFunction	(	const ImageInterface< Complex > &	image,
		const VisBuffer &	vb
	)			`[protected, virtual]`

Find the convolution function.

Reimplemented from casa::FTMachine.

void casa::WProjectFT::findGridSector	(	const Int &	nxp,
		const Int &	nyp,
		const Int &	ixsub,
		const Int &	iysub,
		const Int &	minx,
		const Int &	miny,
		const Int &	icounter,
		Int &	x0,
		Int &	y0,
		Int &	nxsub,
		Int &	nysub,
		const Bool	linear
	)			`[protected]`