Definition of a Measure column in a Table. More...

#include <TableMeasDesc.h>

Inheritance diagram for casa::TableMeasDesc< M >:

Public Member Functions
	TableMeasDesc (const TableMeasValueDesc &)
	Constructor with measure value descriptor.
	TableMeasDesc (const TableMeasValueDesc &, const Vector< Unit > &)
	Constructor with measure value descriptor and Vector of Units.
	TableMeasDesc (const TableMeasValueDesc &, const TableMeasRefDesc &)
	Constructor with value and reference descriptors.
	TableMeasDesc (const TableMeasValueDesc &, const TableMeasRefDesc &, const Vector< Unit > &)
	Constructor with value and reference descriptors and Vector of Units.
virtual TableMeasDescBase *	clone () const
	Clone the object.
	TableMeasDesc (const TableMeasDesc< M > &that)
	Copy constructor (copy semantics).
	~TableMeasDesc ()
TableMeasDesc< M > &	operator= (const TableMeasDesc< M > &that)
	Assignment operator (copy semantics)

Detailed Description

template<class M>
class casa::TableMeasDesc< M >

Definition of a Measure column in a Table.

Intended use:

Public interface

Review Status

Reviewed By:: Bob Garwood
Date Reviewed:: 1999/12/23
Test programs:: tTableMeasures

Prerequisite

Measures
Tables

Synopsis

The TableMeasures system was created to add support for Measure columns to the AIPS++ Table system. Measures are not a fundamental type of the Tables system and hence cannot be represented directly. Instead a Measure column can be created with the aid of the TableMeasDesc class hierarchy. The TableMeasDesc class hierarchy creates a Measure column by associating some number of fundamental data type Table columns into a unit. The associations between these columns is represented in the column keywords of each of the columns which make up a specific Measure column.

Creating and using Measure columns is a three step process:

For each Measure column some number of columns are defined and added to the Table descriptor.
A TableMeasDesc object is used to define a (empty) Measure column from the columns created in the first step.
(RO)ScalarMeasColumns or (RO)ArrayMeasColumns objects are used to access the Measure column for the reading and writing of Measures.

Defining a Measure column (that is, steps 1 and 2 above) is the more complex operation. However, for each Measure column it is a once only operation. After a Measure column has been created its subsequent use is not much different to using "ordinary" Table columns. For information on how to use a Measure column see the (RO)ScalarMeasColumns and (RO)ArrayMeasColumns classes.

The TableMeasDesc class hierarchy contains classes for defining each component of the Measures to be contained in column. A TableMeasOffsetDesc is used to specify the offset component, a TableMeasRefDesc to set up the reference code component and a TableMeasValueDesc names the column used as the main Measure column through which the Measure column is subsequently accessed.
The final step needed to create a Measure column is the creation of a TableMeasDesc object whose constructor takes a TableMeasValueDesc and (optionally) a TableMeasRefDesc. After construction the TableMeasDesc object's write() member is used to make the the Measure column persistent within the Table.

The following examples demonstrate the creation of Measure columns using the above components. Further details about each of these components is available with each class description.
All examples write the measure description into a TableDesc object, i.e. the argument used in the TableMeasDesc::write function is a TableDesc object. It is, however, also possible to write them into a Table object which is useful if measure columns are added to an already existing table (see example 2).

Example

The following creates a MEpoch column with a fixed reference.

       // Need a table to work with.
       TableDesc td("measureTable_desc", "1", TableDesc::New);
       td.comment() = "A test of TableMeasures class.";
   
       // Define a column and add it to the table
       // The main measure column is always an Array column of type Double
       ArrayColumnDesc<Double> cdTime("Time", "An MEpoch column");
       td.addColumn(cdtime);
   
       // Create the Measure column for an MEpoch.  The MEpoch in
       // the column has reference code MEpoch::TAI
       TableMeasRefDesc measRef(MEpoch::TAI);
       TableMeasValueDesc measVal(td, "Time");
       TableMeasDesc<MEpoch> mepochCol(measVal, measRef);
       // write makes the Measure column persistent.
       mepochCol.write(td);
   
       // create the table with 5 rows
       SetupNewTable newtab("MeasuresTable", td, Table::New);
       Table tab(newtab, 5);

Same as example above, but for an already existing table.

       // Need a table to work with.
       TableDesc td("measureTable_desc", "1", TableDesc::New);
       td.comment() = "A test of TableMeasures class.";
   
       // Define a column and add it to the table
       // The main measure column is always an Array column of type Double
       ArrayColumnDesc<Double> cdTime("Time", "An MEpoch column");
       td.addColumn(cdtime);
   
       // create the table with 5 rows
       SetupNewTable newtab("MeasuresTable", td, Table::New);
       Table tab(newtab, 5);
   
       // Create the Measure column for an MEpoch.  The MEpoch in
       // the column has reference code MEpoch::TAI
       TableMeasRefDesc measRef(MEpoch::TAI);
       TableMeasValueDesc measVal(tab.tableDesc(), "Time");
       TableMeasDesc<MEpoch> mepochCol(measVal, measRef);
       // write makes the Measure column persistent.
       mepochCol.write(tab);

An MEpoch column with a variable reference code with a fixed offset:

       // The following three columns will be used to set up a Scalar MEpoch
       // column with variable references and offsets.  3 columns are needed.
       // The "main" column where the MEpoch will be stored
       ArrayColumnDesc<Double> cdTime("Time", "An MEpoch column");
   
       // Variable (i.e., per row) reference code storage needs a column.
       // The column type is either Int or String (Int is faster but String
       // may be useful when browsing the table).  Either a Scalar column or
       // Array column can be used here dependent on whether a Scalar or
       // Array Measure column is used and whether in case of an Array Measure
       // column the reference code has to be variable per array element.
       ScalarColumnDesc<Int> cdRef("TimeRef", "Reference column for Time");
   
       // add the columns to the Table decriptor
       td.addColumn(cdTime);
       td.addColumn(cdRef);
   
       // now create the MEpoch column.
       // want a fixed offset.  Offsets are Measures
       MEpoch offset(MVEpoch(MVTime(1996, 5, 17), MEpoch::UTC);
       TableMeasOffsetDesc offsetDesc(offset);
       // the reference
       TableMeasRefDesc measRef(td, "TimeRef", offsetDesc);
       // the value descriptor, create and write the column
       TableMeasValueDesc measVal(td, "Time");
       TableMeasDesc<MEpoch> mepochCol(measVal, measRef);
       mepochCol.write();
   
       // create the table, etc
       ..\.

An MEpoch column with a variable reference code and offset

       // Variable (per row storage of) offsets needs its own column. Measure
       // offsets are Measures therefore a Measure column is needed.
       ArrayColumnDesc<Double> cdOffset("OffsetCol", "Variable Offset col");
   
       // A column for the variable reference code
       ScalarColumnDesc<String> cdRef("RefCol", "Variable reference column");
   
       // The main (value) column for the Measure column
       ArrayColumnDesc<Double> cdTime("Time", "MEpoch column");
   
       // add the column descriptors to the table
       td.addColumn(cdOffset);
       td.addColumn(cdRef);
       td.addColumn(cdTime);
   
       // Create the Measure column
   
       // The offset column is itself a Measure column, but write() is not
       // called
       TableMeasValueDesc offsetVal(td, "OffsetCol");
       TableMeasDesc<MEpoch> offset(offsetVal);
       TableMeasOffsetDesc offsetDesc(offset);
   
       // the reference
       TableMeasRefDesc ref(td, "RefCol", offsetDesc);
   
       // create the Measure column
       TableMeasValueDesc val(td, "Time");
       TableMeasDesc<MEpoch> mepochCol(val, ref);
       mepochCol.write();
   
       // create the table, etc
       ..\.

Motivation

Creating the required keyword for the definition of a Measure in a Table is somewhat complicated. This class assists in that process.

Thrown Exceptions

AipsError if a reference code string is invalid.

Definition at line 258 of file TableMeasDesc.h.

Constructor & Destructor Documentation

template<class M>

casa::TableMeasDesc< M >::TableMeasDesc ( const TableMeasValueDesc & )

Constructor with measure value descriptor.

The Measure reference for the column will be the default reference code for M. Units for the column will be the default for the Measure type.

template<class M>

casa::TableMeasDesc< M >::TableMeasDesc	(	const TableMeasValueDesc &	,
		const Vector< Unit > &
	)

Constructor with measure value descriptor and Vector of Units.

The Measure reference for the column will be the default reference code for the Measure type. Number of Units must be compatible with the Measure.

template<class M>

casa::TableMeasDesc< M >::TableMeasDesc	(	const TableMeasValueDesc &	,
		const TableMeasRefDesc &
	)

Constructor with value and reference descriptors.

Units for the column will be the default for Measure type.

template<class M>

casa::TableMeasDesc< M >::TableMeasDesc	(	const TableMeasValueDesc &	,
		const TableMeasRefDesc &	,
		const Vector< Unit > &
	)

Constructor with value and reference descriptors and Vector of Units.

Number of Units must be compatible with the Measure.

template<class M>

casa::TableMeasDesc< M >::TableMeasDesc ( const TableMeasDesc< M > & that )

Copy constructor (copy semantics).

template<class M>

casa::TableMeasDesc< M >::~TableMeasDesc ( )

Member Function Documentation

template<class M>

virtual TableMeasDescBase* casa::TableMeasDesc< M >::clone ( ) const [virtual]

Clone the object.

Reimplemented from casa::TableMeasDescBase.

template<class M>

TableMeasDesc<M>& casa::TableMeasDesc< M >::operator= ( const TableMeasDesc< M > & that )

Assignment operator (copy semantics)

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

casacore/measures/TableMeasures/TableMeasDesc.h

Public Member Functions

Detailed Description

template<class M> class casa::TableMeasDesc< M >

Intended use:

Review Status

Prerequisite

Synopsis

Example

Motivation

Thrown Exceptions

Constructor & Destructor Documentation

Member Function Documentation

template<class M>
class casa::TableMeasDesc< M >