ScaledArrayEngine.h

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//# ScaledArrayEngine.h: Templated virtual column engine to scale a table array
//# Copyright (C) 1994,1995,1996,1999,2001
//# Associated Universities, Inc. Washington DC, USA.
//#
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//# $Id: ScaledArrayEngine.h 21298 2012-12-07 14:53:03Z gervandiepen $

#ifndef TABLES_SCALEDARRAYENGINE_H
#define TABLES_SCALEDARRAYENGINE_H

//# Includes
#include <tables/Tables/BaseMappedArrayEngine.h>

namespace casa { //# NAMESPACE CASA - BEGIN

//# Forward Declarations
template<class T> class ScalarColumn;



// <summary>
// Templated virtual column engine to scale a table array
// </summary>

// <use visibility=export>

// <reviewed reviewer="Gareth Hunt" date="94Nov17" tests="">
// </reviewed>

// <prerequisite>
//# Classes you should understand before using this one.
//   <li> VirtualColumnEngine
//   <li> VirtualArrayColumn
// </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:
// <ul>
//  <li> As a fixed value which is used for all arrays in the column.
//  <li> 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.
// </ul>
// 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:
// <br><src> True_value = Stored_value * scale + offset; </src>
//
// 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.
// </synopsis> 

// <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.
// </motivation>

// <example>
// <srcblock>
// // 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)
// }
// </srcblock>
// </example>

// <templating arg=VirtualType>
//  <li> only suited for built-in numerics data types
// </templating>
// <templating arg=StoredType>
//  <li> only suited for built-in numerics data types
// </templating>

template<class VirtualType, class StoredType> class ScaledArrayEngine : public BaseMappedArrayEngine<VirtualType, StoredType>
{
  //# Make members of parent class known.
public:
  using BaseMappedArrayEngine<VirtualType,StoredType>::virtualName;
protected:
  using BaseMappedArrayEngine<VirtualType,StoredType>::storedName;
  using BaseMappedArrayEngine<VirtualType,StoredType>::table;
  using BaseMappedArrayEngine<VirtualType,StoredType>::roColumn;
  using BaseMappedArrayEngine<VirtualType,StoredType>::rwColumn;
  using BaseMappedArrayEngine<VirtualType,StoredType>::setNames;

public:
    // 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 StoredType.
    // The virtual column using this engine must have data type VirtualType.
    ScaledArrayEngine (const String& virtualColumnName,
                       const String& storedColumnName,
                       VirtualType scale,
                       VirtualType offset = 0);

    // 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 StoredType.
    // The virtual column using this engine must have data type VirtualType.
    // <group>
    ScaledArrayEngine (const String& virtualColumnName,
                       const String& storedColumnName,
                       const String& scaleColumnName,
                       VirtualType offset = 0);
    ScaledArrayEngine (const String& virtualColumnName,
                       const String& storedColumnName,
                       const String& scaleColumnName,
                       const String& offsetColumnName);
    // </group>

    // Construct from a record specification as created by getmanagerSpec().
    ScaledArrayEngine (const Record& spec);

    // Destructor is mandatory.
    ~ScaledArrayEngine();

    // Return the type name of the engine (i.e. its class name).
    virtual String dataManagerType() const;

    // Get the name given to the engine (is the virtual column name).
    virtual String dataManagerName() const;
  
    // Record a record containing data manager specifications.
    virtual Record dataManagerSpec() const;

    // Return the name of the class.
    // This includes the names of the template arguments.
    static String className();

    // Register the class name and the static makeObject "constructor".
    // This will make the engine known to the table system.
    // The automatically invoked registration function in DataManReg.cc
    // contains ScaledArrayEngine<double,Int>.
    // Any other instantiation of this class must be registered "manually"
    // (or added to DataManReg.cc).
    static void registerClass();

private:
    // Copy constructor is only used by clone().
    // (so it is made private).
    ScaledArrayEngine (const ScaledArrayEngine<VirtualType,StoredType>&);

    // Assignment is not needed and therefore forbidden
    // (so it is made private and not implemented).
    ScaledArrayEngine<VirtualType,StoredType>& operator=
                           (const ScaledArrayEngine<VirtualType,StoredType>&);

    // Clone the engine object.
    DataManager* clone() const;

    // Initialize the object for a new table.
    // It defines the keywords containing the engine parameters.
    void create (uInt initialNrrow);

    // 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.
    void prepare();

    // Get an array in the given row.
    // This will scale and offset from the underlying array.
    void getArray (uInt rownr, Array<VirtualType>& array);

    // Put an array in the given row.
    // This will scale and offset to the underlying array.
    void putArray (uInt rownr, const Array<VirtualType>& array);

    // Get a section of the array in the given row.
    // This will scale and offset from the underlying array.
    void getSlice (uInt rownr, const Slicer& slicer, Array<VirtualType>& array);

    // Put into a section of the array in the given row.
    // This will scale and offset to the underlying array.
    void putSlice (uInt rownr, const Slicer& slicer,
                   const Array<VirtualType>& array);

    // Get an entire column.
    // This will scale and offset from the underlying array.
    void getArrayColumn (Array<VirtualType>& array);

    // Put an entire column.
    // This will scale and offset to the underlying array.
    void putArrayColumn (const Array<VirtualType>& array);

    // Get a section of all arrays in the column.
    // This will scale and offset from the underlying array.
    void getColumnSlice (const Slicer& slicer, Array<VirtualType>& array);

    // Put a section of all arrays in the column.
    // This will scale and offset to the underlying array.
    void putColumnSlice (const Slicer& slicer, const Array<VirtualType>& array);

    // Scale and/or offset stored to array.
    // This is meant when reading an array from the stored column.
    // It optimizes for scale=1 and/or offset=0.
    void scaleOnGet (VirtualType scale, VirtualType offset,
                     Array<VirtualType>& array,
                     const Array<StoredType>& stored);

    // Scale and/or offset array to stored.
    // This is meant when writing an array into the stored column.
    // It optimizes for scale=1 and/or offset=0.
    void scaleOnPut (VirtualType scale, VirtualType offset,
                     const Array<VirtualType>& array,
                     Array<StoredType>& stored);

    // Scale and/or offset stored 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 scaleColumnOnGet (Array<VirtualType>& array,
                           const Array<StoredType>& stored);

    // Scale and/or offset array to stored 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 scaleColumnOnPut (const Array<VirtualType>& array,
                           Array<StoredType>& stored);


    //# Now define the data members.
    String         scaleName_p;          //# name of scale column
    String         offsetName_p;         //# name of offset column
    VirtualType    scale_p;              //# scale factor
    VirtualType    offset_p;             //# offset value
    Bool           fixedScale_p;         //# scale is a fixed column
    Bool           fixedOffset_p;        //# scale is a fixed column
    ScalarColumn<VirtualType>* scaleColumn_p;  //# column with scale value
    ScalarColumn<VirtualType>* offsetColumn_p; //# column with offset value

    // Get the scale value for this row.
    VirtualType getScale (uInt rownr);

    // Get the offset value for this row.
    VirtualType getOffset (uInt rownr);

public:
    //*display 4
    // 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 DataManReg.cc. 
    // That function gets automatically invoked by the table system.
    static DataManager* makeObject (const String& dataManagerType,
                                    const Record& spec);
};



} //# NAMESPACE CASA - END

#ifndef CASACORE_NO_AUTO_TEMPLATES
#include <tables/Tables/ScaledArrayEngine.tcc>
#endif //# CASACORE_NO_AUTO_TEMPLATES
#endif