Templated virtual column engine to scale a table array. More...

#include <ScaledArrayEngine.h>

Inheritance diagram for casa::ScaledArrayEngine< VirtualType, StoredType >:

Public Member Functions
	ScaledArrayEngine (const String &virtualColumnName, const String &storedColumnName, VirtualType scale, VirtualType offset=0)
	Construct an engine to scale all arrays in a column with the given offset and scale factor.
	ScaledArrayEngine (const String &virtualColumnName, const String &storedColumnName, const String &scaleColumnName, VirtualType offset=0)
	Construct an engine to scale the arrays in a column.
	ScaledArrayEngine (const String &virtualColumnName, const String &storedColumnName, const String &scaleColumnName, const String &offsetColumnName)
	ScaledArrayEngine (const Record &spec)
	Construct from a record specification as created by getmanagerSpec().
	~ScaledArrayEngine ()
	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)
Private Member Functions
	ScaledArrayEngine (const ScaledArrayEngine< VirtualType, StoredType > &)
	Copy constructor is only used by clone().
ScaledArrayEngine< VirtualType, StoredType > &	operator= (const ScaledArrayEngine< VirtualType, StoredType > &)
	Assignment is not needed and therefore forbidden (so it is made private and not implemented).
DataManager *	clone () const
	Clone the engine object.
void	create (uInt initialNrrow)
	Initialize the object for a new table.
void	prepare ()
	Preparing consists of setting the writable switch and adding the initial number of rows in case of create.
void	getArray (uInt rownr, Array< VirtualType > &array)
	Get an array in the given row.
void	putArray (uInt rownr, const Array< VirtualType > &array)
	Put an array in the given row.
void	getSlice (uInt rownr, const Slicer &slicer, Array< VirtualType > &array)
	Get a section of the array in the given row.
void	putSlice (uInt rownr, const Slicer &slicer, const Array< VirtualType > &array)
	Put into a section of the array in the given row.
void	getArrayColumn (Array< VirtualType > &array)
	Get an entire column.
void	putArrayColumn (const Array< VirtualType > &array)
	Put an entire column.
void	getColumnSlice (const Slicer &slicer, Array< VirtualType > &array)
	Get a section of all arrays in the column.
void	putColumnSlice (const Slicer &slicer, const Array< VirtualType > &array)
	Put a section of all arrays in the column.
void	scaleOnGet (VirtualType scale, VirtualType offset, Array< VirtualType > &array, const Array< StoredType > &stored)
	Scale and/or offset stored to array.
void	scaleOnPut (VirtualType scale, VirtualType offset, const Array< VirtualType > &array, Array< StoredType > &stored)
	Scale and/or offset array to stored.
void	scaleColumnOnGet (Array< VirtualType > &array, const Array< StoredType > &stored)
	Scale and/or offset stored to array for the entire column.
void	scaleColumnOnPut (const Array< VirtualType > &array, Array< StoredType > &stored)
	Scale and/or offset array to stored for the entire column.
VirtualType	getScale (uInt rownr)
	Get the scale value for this row.
VirtualType	getOffset (uInt rownr)
	Get the offset value for this row.
Private Attributes
String	scaleName_p
String	offsetName_p
VirtualType	scale_p
VirtualType	offset_p
Bool	fixedScale_p
Bool	fixedOffset_p
ScalarColumn< VirtualType > *	scaleColumn_p
ScalarColumn< VirtualType > *	offsetColumn_p

Detailed Description

template<class VirtualType, class StoredType>
class casa::ScaledArrayEngine< VirtualType, StoredType >

Templated virtual column engine to scale a table array.

Intended use:

Public interface

Review Status

Reviewed By:: Gareth Hunt
Date Reviewed:: 94Nov17

Prerequisite

Synopsis

ScaledArrayEngine 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 value can be given in two ways:

As a fixed value which is used for all arrays in the column.
As the name of a column. In this way each array in a column can have its own scale and offset value. The scale and offset value in a row must be put before the array is put and should not be changed anymore.

It is also possible to have a variable scale factor with a fixed offset value. 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. It adds the scale and offset value on a per row basis.

Because the engine can serve only one column, it was possible to combine the engine and the column functionality in one class. This has been achieved using multiple inheritance. The advantage of this is that only one templated class is used, so less template instantiations are needed.

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<Int> ("storedArray"));
    tableDesc.addColumn (ArrayColumnDesc<double> ("virtualArray"));
   
    // Create a new table using the table description.
    SetupNewTable newtab (tableDesc, "tab.data", Table::New);
   
    // Create the array scaling engine to scale from double to Int
    // and bind it to the double column.
    // Create the table.
    ScaledArrayEngine<double,Int> scalingEngine("virtualArray",
                                                "storedArray", 10);
    newtab.bindColumn ("virtualArray", scalingEngine);
    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)
    }

Template Type Argument Requirements (VirtualType)

only suited for built-in numerics data types