casacore::TableMeasOffsetDesc Class Reference

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#include <TableMeasOffsetDesc.h>

Public Member Functions
	TableMeasOffsetDesc (const Measure &offset)
	Constructor which defines a constant (non-variable) offset.
	TableMeasOffsetDesc (const TableMeasDescBase &offsetColumn, Bool asArray=False)
	Constructor for defining a variable offset.
	TableMeasOffsetDesc (const TableMeasOffsetDesc &that)
	Copy constructor (copy semantics).
	~TableMeasOffsetDesc ()
TableMeasOffsetDesc &	operator= (const TableMeasOffsetDesc &that)
	Assignment operator (copy semantics).
const Measure &	getOffset () const
	Get the (non-variable) measure offset for this column.
Bool	isVariable () const
	Returns True if the offset varies per row.
Bool	isArray () const
	Returns True if the offset varies per array element.
const String &	columnName () const
	Gets the name of the column which stores the variable offset.
void	resetOffset (const Measure &offset)
	Reset the offset.
void	write (TableDesc &, TableRecord &measInfo, const String &prefix)
	Write the information into the record.
void	write (Table &, TableRecord &measInfo, const String &prefix)

Static Public Member Functions
static TableMeasOffsetDesc *	reconstruct (const TableRecord &measInfo, const String &prefix, const Table &tab)
	Reconstructs the TableMeasOffsetDesc from the measInfo TableRecord.

Private Member Functions
	TableMeasOffsetDesc (const TableRecord &measInfo, const String &prefix, const Table &)
	Constructor which uses the measInfo TableRecord.
void	writeKeys (TableRecord &measInfo, const String &prefix)
	Write the actual keywords.

Private Attributes
TableMeasDescBase *	itsTMDesc
MeasureHolder	itsMeasure
String	itsVarColName
Bool	itsVarPerArr

Detailed Description

Definition of a Measure Offset in a Table.

Intended use:

Public interface

Review Status

Reviewed By:

Bob Garwood

Date Reviewed:

1999/12/23

Test programs:

tTableMeasures

Prerequisite

• Measures
• Tables
• TableMeasDesc

Synopsis

This class assists in the definition of the offset component of a TableMeasDesc in the TableMeasures system. Four possibilities exist for specifying the handling of measure offsets in a Measure column. These are:

• an offset is not used
• all measures in the column have the same offset
• a unique (and probably different) offset is stored for each row
• a unique offset is stored in each array element per (Array)column row

Note that this last option is only relevant when using ArrayMeasColumns.

Examples of each of these follow.

Example

1. Specifying a single fixed offset. Note that a Measure offset is itself a measure

   // create an MEpoch to use as the offset in an MEpoch column
   MEpoch offset(MVEpoch(MVTime(1996, 5, 17, (8+18./60.)/24.)), MEpoch::UTC);
   TableMeasOffsetDesc offsetDesc(offset);

2. Storing an offset per row needs an offset column. Measure offsets are Measures so a Measure column is needed:

    // Need a column for the offsets.  This is to be a Measure column,
    // so the rules for creating a Measure column apply.
    ArrayColumnDesc<Double> cdOffset("OffsetCol", "Variable Offset col");
   ..\.
    // add the column to the table
    td.addColumn(cdOffset);
   ..\.
    // Create the Measure column to be used as the measure offset column
    TableMeasValueDesc valDesc(td, "OffsetCol");
    TableMeasDesc<MEpoch> offset(valDesc);
    // Create the offset descriptor
    TableMeasOffsetDesc offsetDesc(offset);

3. Storing an offset per array element per row requires one change in the constructor used in the previous example:

   ..\.
    // set up column and TableMeasDesc as before
   ..\.
    // Setting the asArray parameter to True in the constructor specifies
    // per element offset storage
    TableMeasOffsetDesc offsetDesc(offset, True);

For an example of the use of the TableMeasOffsetDesc class in the context of a full TableMeasDesc declaration see class TableMeasDesc.

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 during reconstruction of non-variable offset if a component of the offset measure is missing in the column keywords or is corrupt in some way.
• AipsError if getOffset() called on a variable offset object.
• AipsError during a reconstruct if the column doesn't have a Unit.

Definition at line 143 of file TableMeasOffsetDesc.h.

Constructor & Destructor Documentation

TableMeasOffsetDesc() [1/4]

casacore::TableMeasOffsetDesc::TableMeasOffsetDesc

(

const Measure &

offset

)

Constructor which defines a constant (non-variable) offset.

All measures in the columns will have the same offset.

References casacore::offset().

Referenced by operator=(), reconstruct(), and TableMeasOffsetDesc().

TableMeasOffsetDesc() [2/4]

casacore::TableMeasOffsetDesc::TableMeasOffsetDesc	(	const TableMeasDescBase &	offsetColumn,
		Bool	asArray = False )

Constructor for defining a variable offset.

If asArray is True then the offset is stored per array element. The default is for the offset to be stored (and hence variable) per row.

References casacore::False.

TableMeasOffsetDesc() [3/4]

casacore::TableMeasOffsetDesc::TableMeasOffsetDesc

(

const TableMeasOffsetDesc &

that

)

Copy constructor (copy semantics).

References TableMeasOffsetDesc().

~TableMeasOffsetDesc()

casacore::TableMeasOffsetDesc::~TableMeasOffsetDesc

(

)

TableMeasOffsetDesc() [4/4]

casacore::TableMeasOffsetDesc::TableMeasOffsetDesc ( const TableRecord & measInfo, const String & prefix, const Table &  )

private

Constructor which uses the measInfo TableRecord.

Member Function Documentation

columnName()

const String & casacore::TableMeasOffsetDesc::columnName ( ) const

inline

Gets the name of the column which stores the variable offset.

"" is returned if the offset is not variable.

Definition at line 183 of file TableMeasOffsetDesc.h.

References itsVarColName.

getOffset()

const Measure & casacore::TableMeasOffsetDesc::getOffset

(

)

const

Get the (non-variable) measure offset for this column.

If it doesn't exist (thus if the offset is variable), an exception is thrown.

isArray()

Bool casacore::TableMeasOffsetDesc::isArray ( ) const

inline

Returns True if the offset varies per array element.

Definition at line 178 of file TableMeasOffsetDesc.h.

References isVariable(), and itsVarPerArr.

isVariable()

Bool casacore::TableMeasOffsetDesc::isVariable ( ) const

inline

Returns True if the offset varies per row.

Definition at line 174 of file TableMeasOffsetDesc.h.

References itsTMDesc.

Referenced by isArray().

operator=()

TableMeasOffsetDesc & casacore::TableMeasOffsetDesc::operator=

(

const TableMeasOffsetDesc &

that

)

Assignment operator (copy semantics).

References TableMeasOffsetDesc().

reconstruct()

TableMeasOffsetDesc * casacore::TableMeasOffsetDesc::reconstruct ( const TableRecord & measInfo, const String & prefix, const Table & tab )

static

Reconstructs the TableMeasOffsetDesc from the measInfo TableRecord.

References TableMeasOffsetDesc().

resetOffset()

void casacore::TableMeasOffsetDesc::resetOffset

(

const Measure &

offset

)

Reset the offset.

It overwrites the value used when defining the TableMeasDesc. It is only possible if it was defined as fixed for the entire column.

References casacore::offset().

write() [1/2]

void casacore::TableMeasOffsetDesc::write	(	Table &	,
		TableRecord &	measInfo,
		const String &	prefix )

write() [2/2]

void casacore::TableMeasOffsetDesc::write	(	TableDesc &	,
		TableRecord &	measInfo,
		const String &	prefix )

Write the information into the record.

writeKeys()

void casacore::TableMeasOffsetDesc::writeKeys ( TableRecord & measInfo, const String & prefix )

private

Write the actual keywords.

Member Data Documentation

itsMeasure

MeasureHolder casacore::TableMeasOffsetDesc::itsMeasure

private

Definition at line 199 of file TableMeasOffsetDesc.h.

itsTMDesc

TableMeasDescBase* casacore::TableMeasOffsetDesc::itsTMDesc

private

Definition at line 198 of file TableMeasOffsetDesc.h.

Referenced by isVariable().

itsVarColName

String casacore::TableMeasOffsetDesc::itsVarColName

private

Definition at line 200 of file TableMeasOffsetDesc.h.

Referenced by columnName().

itsVarPerArr

Bool casacore::TableMeasOffsetDesc::itsVarPerArr

private

Definition at line 201 of file TableMeasOffsetDesc.h.

Referenced by isArray().

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

• measures/TableMeasures/TableMeasOffsetDesc.h