Virtual column engine to scale a table float array. More...

#include <CompressFloat.h>

Inheritance diagram for casa::CompressFloat:

Public Member Functions
	CompressFloat (const String &virtualColumnName, const String &storedColumnName, Float scale, Float offset=0)
	Construct an engine to scale all arrays in a column with the given offset and scale factor.
	CompressFloat (const String &virtualColumnName, const String &storedColumnName, const String &scaleColumnName, const String &offsetColumnName, Bool autoScale=True)
	Construct an engine to scale the arrays in a column.
	CompressFloat (const Record &spec)
	Construct from a record specification as created by getmanagerSpec().
	~CompressFloat ()
	Destructor is mandatory.
virtual String	dataManagerType () const
	Return the type name of the engine (i.e.
virtual String	dataManagerName () const
	Get the name given to the engine (is the virtual column name).
virtual Record	dataManagerSpec () const
	Record a record containing data manager specifications.
Static Public Member Functions
static String	className ()
	Return the name of the class.
static void	registerClass ()
	Register the class name and the static makeObject "constructor".
static DataManager *	makeObject (const String &dataManagerType, const Record &spec)
	Define the "constructor" to construct this engine when a table is read back.
Private Member Functions
	CompressFloat (const CompressFloat &)
	Copy constructor is only used by clone().
CompressFloat &	operator= (const CompressFloat &)
	Assignment is not needed and therefore forbidden (so it is made private and not implemented).
virtual DataManager *	clone () const
	Clone the engine object.
virtual void	create (uInt initialNrrow)
	Initialize the object for a new table.
virtual void	prepare ()
	Preparing consists of setting the writable switch and adding the initial number of rows in case of create.
virtual void	reopenRW ()
	Reopen the engine for read/write access.
virtual void	addRowInit (uInt startRow, uInt nrrow)
	Add rows to the table.
virtual void	getArray (uInt rownr, Array< Float > &array)
	Get an array in the given row.
virtual void	putArray (uInt rownr, const Array< Float > &array)
	Put an array in the given row.
virtual void	getSlice (uInt rownr, const Slicer &slicer, Array< Float > &array)
	Get a section of the array in the given row.
virtual void	putSlice (uInt rownr, const Slicer &slicer, const Array< Float > &array)
	Put into a section of the array in the given row.
virtual void	getArrayColumn (Array< Float > &array)
	Get an entire column.
virtual void	putArrayColumn (const Array< Float > &array)
	Put an entire column.
virtual void	getColumnSlice (const Slicer &slicer, Array< Float > &array)
	Get a section of all arrays in the column.
virtual void	putColumnSlice (const Slicer &slicer, const Array< Float > &array)
	Put a section of all arrays in the column.
void	scaleOnGet (Float scale, Float offset, Array< Float > &array, const Array< Short > &target)
	Scale and/or offset target to array.
void	scaleOnPut (Float scale, Float offset, const Array< Float > &array, Array< Short > &target)
	Scale and/or offset array to target.
void	scaleColumnOnGet (Array< Float > &array, const Array< Short > &target)
	Scale and/or offset target to array for the entire column.
void	scaleColumnOnPut (const Array< Float > &array, Array< Short > &target)
	Scale and/or offset array to target for the entire column.
Float	getScale (uInt rownr)
	Get the scale value for this row.
Float	getOffset (uInt rownr)
	Get the offset value for this row.
void	findMinMax (Float &minVal, Float &maxVal, const Array< Float > &array) const
	Find minimum and maximum from the array data.
void	makeScaleOffset (Float &scale, Float &offset, Float minVal, Float maxVal) const
	Make scale and offset from the minimum and maximum of the array data.
void	putPart (uInt rownr, const Slicer &slicer, const Array< Float > &array, Float scale, Float offset)
	Put a part of an array in a row using given scale/offset values.
void	putFullPart (uInt rownr, const Slicer &slicer, Array< Float > &fullArray, const Array< Float > &partArray, Float minVal, Float maxVal)
	Fill the array part into the full array and put it using the given min/max values.
Private Attributes
String	scaleName_p
String	offsetName_p
Float	scale_p
Float	offset_p
Bool	fixed_p
Bool	autoScale_p
ROScalarColumn< Float > *	scaleColumn_p
ROScalarColumn< Float > *	offsetColumn_p
ScalarColumn< Float > *	rwScaleColumn_p
ScalarColumn< Float > *	rwOffsetColumn_p
Array< Short >	buffer_p

Detailed Description

Virtual column engine to scale a table float array.

Intended use:

Public interface

Review Status

Reviewed By:: UNKNOWN
Date Reviewed:: before2004/08/25
Test programs:: tCompressFloat

Prerequisite

Synopsis

CompressFloat is a virtual column engine which scales an array of one type to another type to save disk storage. This resembles the classic AIPS compress method which scales the data from float to short. The scale factor and offset values can be given in two ways:

As a fixed values which is used for all arrays in the column. These values have to be given when constructing of the engine.
As the name of a column. In this way each array in the column has its own scale and offset value. By default it uses auto-scaling (see below). Otherwise the scale and offset value in a row must be put before the array is put and should not be changed anymore.

Auto-scaling means that the engine will determine the scale and offset value itself when an array (or a slice) is put. It does it by mapping the values in the array to the range [-32767,32767]. At each put the scale/offset values are changed as needed. Note that with auto-scaling putSlice can be somewhat slower, because the entire array might need to be rescaled.

As in FITS the scale and offset values are used as:
True_value = Stored_value * scale + offset;

An engine object should be used for one column only, because the stored column name is part of the engine. If it would be used for more than one column, they would all share the same stored column. When the engine is bound to a column, it is checked if the name of that column matches the given virtual column name.

The engine can be used for a column containing any kind of array (thus direct or indirect, fixed or variable shaped)) as long as the virtual array can be stored in the stored array. Thus a fixed shaped virtual can use a variable shaped stored, but not vice versa. A fixed shape indirect virtual can use a stored with direct arrays.

This class can also serve as an example of how to implement a virtual column engine.

Motivation

This class allows to store data in a smaller representation. It is needed to resemble the classic AIPS compress option.

Because the engine can serve only one column, it was possible to combine the engine and the column functionality in one class.

Example

    // Create the table description and 2 columns with indirect arrays in it.
    // The Int column will be stored, while the double will be
    // used as virtual.
    TableDesc tableDesc ("", TableDesc::Scratch);
    tableDesc.addColumn (ArrayColumnDesc<Short> ("storedArray"));
    tableDesc.addColumn (ArrayColumnDesc<Float> ("virtualArray"));
    tableDesc.addColumn (ScalarColumnDesc<Float> ("scale"));
    tableDesc.addColumn (ScalarColumnDesc<Float> ("offset"));
   
    // Create a new table using the table description.
    SetupNewTable newtab (tableDesc, "tab.data", Table::New);
   
    // Create the array scaling engine (with auto-scale)
    // and bind it to the float column.
    CompressFloat scalingEngine("virtualArray", "storedArray",
                                "scale", "offset");
    newtab.bindColumn ("virtualArray", scalingEngine);
    // Create the table.
    Table table (newtab);
   
    // Store a 3-D array (with dim. 2,3,4) into each row of the column.
    // The shape of each array in the column is implicitly set by the put
    // function. This will also set the shape of the underlying Int array.
    ArrayColumn data (table, "virtualArray");
    Array<double> someArray(IPosition(4,2,3,4));
    someArray = 0;
    for (uInt i=0, i<10; i++) {          // table will have 10 rows
        table.addRow();
        data.put (i, someArray)
    }

Definition at line 138 of file CompressFloat.h.

Constructor & Destructor Documentation

casa::CompressFloat::CompressFloat	(	const String &	virtualColumnName,
		const String &	storedColumnName,
		Float	scale,
		Float	offset = `0`
	)

Construct an engine to scale all arrays in a column with the given offset and scale factor.

StoredColumnName is the name of the column where the scaled data will be put and must have data type Short. The virtual column using this engine must have data type Float.

casa::CompressFloat::CompressFloat	(	const String &	virtualColumnName,
		const String &	storedColumnName,
		const String &	scaleColumnName,
		const String &	offsetColumnName,
		Bool	autoScale = `True`
	)

Construct an engine to scale the arrays in a column.

The scale and offset values are taken from a column with the given names. In that way each array has its own scale factor and offset value. An exception is thrown if these columns do not exist. VirtualColumnName is the name of the virtual column and is used to check if the engine gets bound to the correct column. StoredColumnName is the name of the column where the scaled data will be put and must have data type Short. The virtual column using this engine must have data type Float.

casa::CompressFloat::CompressFloat ( const Record & spec )

Construct from a record specification as created by getmanagerSpec().

casa::CompressFloat::~CompressFloat ( )

Destructor is mandatory.

casa::CompressFloat::CompressFloat ( const CompressFloat & ) [private]

Copy constructor is only used by clone().

(so it is made private).

Member Function Documentation

virtual void casa::CompressFloat::addRowInit	(	uInt	startRow,
		uInt	nrrow
	)		`[private, virtual]`

Add rows to the table.

If auto-scaling, it initializes the scale column with 0 to indicate that no data has been processed yet.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

static String casa::CompressFloat::className ( ) [static]

Return the name of the class.

This includes the names of the template arguments.

virtual DataManager* casa::CompressFloat::clone ( ) const [private, virtual]

Clone the engine object.

Implements casa::DataManager.

virtual void casa::CompressFloat::create ( uInt initialNrrow ) [private, virtual]

Initialize the object for a new table.

It defines the keywords containing the engine parameters.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

virtual String casa::CompressFloat::dataManagerName ( ) const [virtual]

Get the name given to the engine (is the virtual column name).

Reimplemented from casa::DataManager.

virtual Record casa::CompressFloat::dataManagerSpec ( ) const [virtual]

Record a record containing data manager specifications.

Reimplemented from casa::DataManager.

virtual String casa::CompressFloat::dataManagerType ( ) const [virtual]

Return the type name of the engine (i.e.

its class name).

Implements casa::DataManager.

void casa::CompressFloat::findMinMax	(	Float &	minVal,
		Float &	maxVal,
		const Array< Float > &	array
	)		const `[private]`

Find minimum and maximum from the array data.

NaN and infinite values are ignored. If no values are finite, minimum and maximum are set to NaN.

virtual void casa::CompressFloat::getArray	(	uInt	rownr,
		Array< Float > &	array
	)		`[private, virtual]`

Get an array in the given row.

This will scale and offset from the underlying array.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

virtual void casa::CompressFloat::getArrayColumn ( Array< Float > & array ) [private, virtual]

Get an entire column.

This will scale and offset from the underlying array.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

virtual void casa::CompressFloat::getColumnSlice	(	const Slicer &	slicer,
		Array< Float > &	array
	)		`[private, virtual]`

Get a section of all arrays in the column.

This will scale and offset from the underlying array.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

Float casa::CompressFloat::getOffset ( uInt rownr ) [inline, private]

Get the offset value for this row.

Definition at line 343 of file CompressFloat.h.

References fixed_p, offset_p, and offsetColumn_p.

Float casa::CompressFloat::getScale ( uInt rownr ) [inline, private]

Get the scale value for this row.

Definition at line 339 of file CompressFloat.h.

References fixed_p, scale_p, and scaleColumn_p.

virtual void casa::CompressFloat::getSlice	(	uInt	rownr,
		const Slicer &	slicer,
		Array< Float > &	array
	)		`[private, virtual]`

Get a section of the array in the given row.

This will scale and offset from the underlying array.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

static DataManager* casa::CompressFloat::makeObject	(	const String &	dataManagerType,
		const Record &	spec
	)		`[static]`

Define the "constructor" to construct this engine when a table is read back.

This "constructor" has to be registered by the user of the engine. If the engine is commonly used, its registration can be added to the registerAllCtor function in DataManager.cc. That function gets automatically invoked by the table system.

void casa::CompressFloat::makeScaleOffset	(	Float &	scale,
		Float &	offset,
		Float	minVal,
		Float	maxVal
	)		const `[private]`

Make scale and offset from the minimum and maximum of the array data.

If minVal is NaN, scale is set to 0.

CompressFloat& casa::CompressFloat::operator= ( const CompressFloat & ) [private]

Assignment is not needed and therefore forbidden (so it is made private and not implemented).

virtual void casa::CompressFloat::prepare ( ) [private, virtual]

Preparing consists of setting the writable switch and adding the initial number of rows in case of create.

Furthermore it reads the keywords containing the engine parameters.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

virtual void casa::CompressFloat::putArray	(	uInt	rownr,
		const Array< Float > &	array
	)		`[private, virtual]`

Put an array in the given row.

This will scale and offset to the underlying array.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

virtual void casa::CompressFloat::putArrayColumn ( const Array< Float > & array ) [private, virtual]

Put an entire column.

This will scale and offset to the underlying array.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

virtual void casa::CompressFloat::putColumnSlice	(	const Slicer &	slicer,
		const Array< Float > &	array
	)		`[private, virtual]`

Put a section of all arrays in the column.

This will scale and offset to the underlying array.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

void casa::CompressFloat::putFullPart	(	uInt	rownr,
		const Slicer &	slicer,
		Array< Float > &	fullArray,
		const Array< Float > &	partArray,
		Float	minVal,
		Float	maxVal
	)		`[private]`

Fill the array part into the full array and put it using the given min/max values.

void casa::CompressFloat::putPart	(	uInt	rownr,
		const Slicer &	slicer,
		const Array< Float > &	array,
		Float	scale,
		Float	offset
	)		`[private]`

Put a part of an array in a row using given scale/offset values.

virtual void casa::CompressFloat::putSlice	(	uInt	rownr,
		const Slicer &	slicer,
		const Array< Float > &	array
	)		`[private, virtual]`

Put into a section of the array in the given row.

This will scale and offset to the underlying array.

Reimplemented from casa::BaseMappedArrayEngine< Float, Short >.

static void casa::CompressFloat::registerClass ( ) [static]

Register the class name and the static makeObject "constructor".

This will make the engine known to the table system.

virtual void casa::CompressFloat::reopenRW ( ) [private, virtual]

Reopen the engine for read/write access.

It makes the column writable if the underlying column is writable.

Reimplemented from casa::DataManager.

void casa::CompressFloat::scaleColumnOnGet	(	Array< Float > &	array,
		const Array< Short > &	target
	)		`[private]`

Scale and/or offset target to array for the entire column.

When the scale and offset are fixed, it will do the entire array. Otherwise it iterates through the array and applies the scale and offset per row.

void casa::CompressFloat::scaleColumnOnPut	(	const Array< Float > &	array,
		Array< Short > &	target
	)		`[private]`

Scale and/or offset array to target for the entire column.

When the scale and offset are fixed, it will do the entire array. Otherwise it iterates through the array and applies the scale and offset per row.

void casa::CompressFloat::scaleOnGet	(	Float	scale,
		Float	offset,
		Array< Float > &	array,
		const Array< Short > &	target
	)		`[private]`

Scale and/or offset target to array.

This is meant when reading an array from the stored column. It optimizes for scale=1 and/or offset=0.

void casa::CompressFloat::scaleOnPut	(	Float	scale,
		Float	offset,
		const Array< Float > &	array,
		Array< Short > &	target
	)		`[private]`

Scale and/or offset array to target.

This is meant when writing an array into the stored column. It optimizes for scale=1 and/or offset=0.

Member Data Documentation

Bool casa::CompressFloat::autoScale_p [private]

Definition at line 291 of file CompressFloat.h.

Array<Short> casa::CompressFloat::buffer_p [private]

Definition at line 296 of file CompressFloat.h.

Bool casa::CompressFloat::fixed_p [private]

Definition at line 290 of file CompressFloat.h.

Referenced by getOffset(), and getScale().

Float casa::CompressFloat::offset_p [private]

Definition at line 289 of file CompressFloat.h.

Referenced by getOffset().

ROScalarColumn<Float>* casa::CompressFloat::offsetColumn_p [private]

Definition at line 293 of file CompressFloat.h.

Referenced by getOffset().

String casa::CompressFloat::offsetName_p [private]

Definition at line 287 of file CompressFloat.h.

ScalarColumn<Float>* casa::CompressFloat::rwOffsetColumn_p [private]

Definition at line 295 of file CompressFloat.h.

ScalarColumn<Float>* casa::CompressFloat::rwScaleColumn_p [private]

Definition at line 294 of file CompressFloat.h.

Float casa::CompressFloat::scale_p [private]

Definition at line 288 of file CompressFloat.h.

Referenced by getScale().

ROScalarColumn<Float>* casa::CompressFloat::scaleColumn_p [private]

Definition at line 292 of file CompressFloat.h.

Referenced by getScale().

String casa::CompressFloat::scaleName_p [private]

Definition at line 286 of file CompressFloat.h.

The documentation for this class was generated from the following file:

casacore/tables/Tables/CompressFloat.h

Public Member Functions

Static Public Member Functions

Private Member Functions

Private Attributes

Detailed Description

Intended use:

Review Status

Prerequisite

Synopsis

Motivation

Example

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation