Creating and using Measure columns is a three step process:
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).
// 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);
// 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);
// 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
...
// 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
...
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.
Constructor with value and reference descriptors. Units for the column will be the default for Measure type.
Constructor with value and reference descriptors and Vector of Units. Number of Units must be compatible with the Measure.
Clone the object.
Copy constructor (copy semantics).
Assignment operator (copy semantics)