MosaicFT.h

Classes

MosaicFT -- An FTMachine for Gridded Fourier transforms (full description)

class MosaicFT : public FTMachine

Interface

Public Members

MosaicFT(MeasurementSet& ms, SkyJones& sj, Long cachesize, Int tilesize=16, Bool usezero=True)

MosaicFT(const RecordInterface& stateRec)

MosaicFT(const MosaicFT &other)

MosaicFT &operator=(const MosaicFT &other)

~MosaicFT()

void initializeToVis(ImageInterface<Complex>& image, const Complex& vb)

void initializeToVis(ImageInterface<Complex>& image, const Complex& vb, VisBuffer<Complex>& griddedVis, Array<Double>& uvscale)

void finalizeToVis()

void initializeToSky(ImageInterface<Complex>& image, Complex<Float>& weight, const Matrix& vb)

void finalizeToSky()

void get(VisBuffer& vb, Int row=-1)

void get(VisBuffer& vb, Cube<Complex>& degrid, Array<Complex>& griddedVis, Array<Double>& scale, Int row=-1)

void put(const VisBuffer& vb, Int row=-1, Bool dopsf=False, FTMachine::Type type=FTMachine::OBSERVED)

void makeImage(FTMachine::Type type, VisSet& vs, ImageInterface<Complex>& image, Complex<Float>& weight)

ImageInterface<Complex>& getImage(Complex<Float>&, Bool normalize=True)

void getWeightImage(ImageInterface<Float>&, Matrix<Float>&)

Bool toRecord(String& error, RecordInterface& outRec, Bool withImage=False)

Bool fromRecord(String& error, const RecordInterface& inRec)

Bool isFourier()

String name()

Protected Members

Int nint(Double val)

void findConvFunction(const ImageInterface<Complex>& image, const Complex& vb)

void addBeamCoverage(ImageInterface<Complex>& image)

Array<Complex>* getDataPointer(const IPosition&, Bool)

void ok()

void init()

Bool recordOnGrid(const VisBuffer& vb, Int rownr) const

Bool checkPBOfField(const VisBuffer& vb)

Int getIndex(const ROMSPointingColumns& mspc, const Double& time, const Double& interval)

Bool getXYPos(const VisBuffer& vb, Int row)

Description

Prerequisite

• FTMachine module
• SkyEquation module
• VisBuffer module

Etymology

Synopsis

Gridding and degridding in MosaicFT 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

Motivation

To Do

Deal with large VLA spectral line case

Member Description

MosaicFT(MeasurementSet& ms, SkyJones& sj, Long cachesize, Int tilesize=16, Bool usezero=True)

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).

MosaicFT(const RecordInterface& stateRec)

Construct from a Record containing the MosaicFT state

MosaicFT(const MosaicFT &other)

Copy constructor

MosaicFT &operator=(const MosaicFT &other)

Assignment operator

~MosaicFT()

void initializeToVis(ImageInterface<Complex>& image, const Complex& vb)

Initialize transform to Visibility plane using the image as a template. The image is loaded and Fourier transformed.

void initializeToVis(ImageInterface<Complex>& image, const Complex& vb, VisBuffer<Complex>& griddedVis, Array<Double>& uvscale)

This version returns the gridded vis...should be used in conjunction with the version of 'get' that needs the gridded visdata

void finalizeToVis()

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

void initializeToSky(ImageInterface<Complex>& image, Complex<Float>& weight, const Matrix& 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. DOES NOT DO THE FINAL TRANSFORM!

void get(VisBuffer& vb, Int row=-1)

Get actual coherence from grid by degridding

void get(VisBuffer& vb, Cube<Complex>& degrid, Array<Complex>& griddedVis, Array<Double>& scale, Int row=-1)

Get the coherence from grid return it in the degrid is used especially when scratch columns are not present in ms.

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, Complex<Float>& weight)

Make the entire image

ImageInterface<Complex>& getImage(Complex<Float>&, Bool normalize=True)

Get the final image: do the Fourier transform and grid-correct, then optionally normalize by the summed weights

void getWeightImage(ImageInterface<Float>&, Matrix<Float>&)

Get the final weights image

Bool toRecord(String& error, RecordInterface& outRec, Bool withImage=False)

Save and restore the MosaicFT to and from a record

Bool fromRecord(String& error, const RecordInterface& inRec)

Bool isFourier()

Can this FTMachine be represented by Fourier convolutions?

String name()

Return name of this machine

Int nint(Double val)

void findConvFunction(const ImageInterface<Complex>& image, const Complex& vb)

Find the convolution function

void addBeamCoverage(ImageInterface<Complex>& image)

Array<Complex>* getDataPointer(const IPosition&, Bool)

Get the appropriate data pointer

void ok()

void init()

Bool recordOnGrid(const VisBuffer& vb, Int rownr) const

Is this record on Grid? check both ends. This assumes that the ends bracket the middle

Bool checkPBOfField(const VisBuffer& vb)

Check whether the convolution function for this field is already done

Int getIndex(const ROMSPointingColumns& mspc, const Double& time, const Double& interval)

Bool getXYPos(const VisBuffer& vb, Int row)