MeasurementSets_module

Handle storage and access of telescope data. More...

Modules
	MeasurementSets_module_internal_classes
	Internal MeasurementSets_module classes and functions.

Classes
class	casacore::MeasurementSet
	A Table intended to hold astronomical data (a set of Measurements). More...
class	casacore::MSAntenna
	A Table intended to hold a MeasurementSet ANTENNA table. More...
class	casacore::MSAntennaColumns
	A class to provide easy access to MSAntenna columns. More...
class	casacore::MSAntennaEnums
	Enums for the MeasurementSet ANTENNA table. More...
class	casacore::MSColumns
	A class to provide easy access to MeasurementSet columns. More...
class	casacore::MSDataDescColumns
	A class to provide easy access to MSDataDescription columns. More...
class	casacore::MSDataDescriptionEnums
	Enums for the MeasurementSet DATA_DESCRIPTION table. More...
class	casacore::MSDataDescription
	A Table intended to hold a MeasurementSet DATADESCRIPTION table. More...
class	casacore::MSDoppler
	A Table intended to hold a MeasurementSet DOPPLER table. More...
class	casacore::MSDopplerColumns
	A class to provide easy access to MSDoppler columns. More...
class	casacore::MSDopplerEnums
	Enums for the MeasurementSet DOPPLER table. More...
class	casacore::MSDopplerUtil
	A utility class for MS Doppler tracking information. More...
class	casacore::MSFeed
	A Table intended to hold a MeasurementSet FEED table. More...
class	casacore::MSFeedColumns
	A class to provide easy access to MSFeed columns. More...
class	casacore::MSFeedEnums
	Enums for the MeasurementSet FEED table. More...
class	casacore::MSField
	A Table intended to hold a MeasurementSet FIELD table. More...
class	casacore::MSFieldColumns
	A class to provide easy access to MSField columns. More...
class	casacore::MSFieldEnums
	Enums for the MeasurementSet FIELD table. More...
class	casacore::MSFlagCmd
	A Table intended to hold a MeasurementSet FLAG_CMD table. More...
class	casacore::MSFlagCmdColumns
	A class to provide easy access to MSFlagCmd columns. More...
class	casacore::MSFlagCmdEnums
	Enums for the MeasurementSet FLAG_CMD table. More...
class	casacore::MSFreqOffsetColumns
	A class to provide easy access to MSFreqOffset columns. More...
class	casacore::MSFreqOffsetEnums
	Enums for the MeasurementSet FREQ_OFFSET table. More...
class	casacore::MSFreqOffset
	A Table intended to hold a MeasurementSet FREQ_OFFSET table. More...
class	casacore::MSHistory
	A Table intended to hold a MeasurementSet OBSERVATIONLOG table. More...
class	casacore::MSHistoryColumns
	A class to provide easy access to MSHistory columns. More...
class	casacore::MSHistoryEnums
	Enums for the MeasurementSet HISTORY table. More...
class	casacore::MSInterval
	Small helper class to specify an 'interval' comparison. More...
class	casacore::MSIter
	An iterator class for MeasurementSets. More...
class	casacore::MSMainColumns
	A class for easy access to MeasurementSet main table columns. More...
class	casacore::MSMainEnums
	Enums for the MeasurementSet main table. More...
class	casacore::MSObservationColumns
	A class to provide easy access to MSObservation columns. More...
class	casacore::MSObservationEnums
	Enums for the MeasurementSet OBSERVATION table. More...
class	casacore::MSObservation
	A Table intended to hold a MeasurementSet OBSERVATION table. More...
class	casacore::MSPointing
	A Table intended to hold a MeasurementSet POINTING table. More...
class	casacore::MSPointingColumns
	A class to provide easy access to MSPointing columns. More...
class	casacore::MSPointingEnums
	Enums for the MeasurementSet POINTING table. More...
class	casacore::MSPolarization
	A Table intended to hold a MeasurementSet POLARIZATION table. More...
class	casacore::MSPolarizationColumns
	A class to provide easy access to MSPolarization columns. More...
class	casacore::MSPolarizationEnums
	Enums for the MeasurementSet POLARIZATION table. More...
class	casacore::MSProcessor
	A Table intended to hold a MeasurementSet PROCESSOR table. More...
class	casacore::MSProcessorColumns
	A class to provide easy access to MSProcessor columns. More...
class	casacore::MSProcessorEnums
	Enums for the MeasurementSet PROCESSER table. More...
class	casacore::MSRange
	MSRange determines ranges of values in a MeasurementSet. More...
class	casacore::MSSource
	A Table intended to hold a MeasurementSet SOURCE table. More...
class	casacore::MSSourceColumns
	A class to provide easy access to MSSource columns. More...
class	casacore::MSSourceEnums
	Enums for the MeasurementSet SOURCE table. More...
class	casacore::MSSpectralWindow
	A Table intended to hold a MeasurementSet SPECTRAL_WINDOW table. More...
class	casacore::MSSpWindowColumns
	A class to provide easy access to MSSpectralWindow columns. More...
class	casacore::MSSpectralWindowEnums
	Enums for the MeasurementSet SPECTRAL_WINDOW table. More...
class	casacore::MSState
	A Table intended to hold a MeasurementSet STATE table. More...
class	casacore::MSStateColumns
	A class to provide easy access to MSState columns. More...
class	casacore::MSStateEnums
	Enums for the MeasurementSet STATE table. More...
class	casacore::MSSysCal
	A Table intended to hold a MeasurementSet SYSCAL table. More...
class	casacore::MSSysCalColumns
	A class to provide easy access to MSSysCal columns. More...
class	casacore::MSSysCalEnums
	Enums for the MeasurementSet SYSCAL table. More...
struct	casacore::MSTableMaps
	A struct holding the maps used in MSTable. More...
class	casacore::MSTable< MSEnum >
	A Table intended to hold astronomical data. More...
class	casacore::MSTileLayout
	An helper class for deciding on tile shapes in MeasurementSets. More...
class	casacore::MSWeather
	A Table intended to hold a MeasurementSet WEATHER table. More...
class	casacore::MSWeatherColumns
	A class to provide easy access to MSWeather columns. More...
class	casacore::MSWeatherEnums
	Enums for the MeasurementSet WEATHER table. More...
class	casacore::StokesConverter
	StokesConverter converts any set of polarizations into any other one. More...

Detailed Description

Handle storage and access of telescope data.

See below for an overview of the classes in this module.

Prerequisite

• Tables module
• Note 229

Review Status

Reviewed By:

Bob Garwood

Date Reviewed:

1997/02/01

Etymology

The MeasurementSet is where all data are ultimately to be found in Casacore. Since, this is a collection of measurements (either actual or simulated), the term MeasurementSet seems appropriate. Often we use the abbreviation (and typedef) MS for MeasurementSet.

Synopsis

The MeasurementSets module handles storage of telescope data and access to it. The MeasurementSet is the class that gives access to the data.

A MeasurementSet (MS) is a Table with subtables stored as keywords. For each of these tables there is a separate class: the main table is MeasurementSet, the subtables are MSAntenna, MSArray, MSFeed, MSField, MSObsLog, MSObservation, MSSource, MSSpectralWindow, MSSysCal, MSWeather.

Class hierarchy and Table layout

Each table has a number of predefined columns and keywords, a subset of which is required to be present. The column and keyword layout of each table is described in Note 229 and in a separate class which contains two enum definitions. The enum classes, e.g., MSMainEnums and MSAntennaEnums, just contain a PredefinedColumn (PDC) enum and a PredefinedKeyword (PDK) enum. These enum definitions are used as template arguments for the generic class MSTable<PDC,PDK> from which MeasurementSet and all the subtable classes are derived. Thus, e.g., the class MSAntenna is derived from MSTable<MSAntennaEnums::PredefinedColumns, MSAntennaEnums::PredefinedKeywords>.

The MSTable class provides a large number of common column and keyword helper functions. They are useful when creating a Table following the MeasurementSet conventions from scratch and assist in following the agreed upon column and keyword naming conventions.

MSTable in turn is derived from Table, thus all the MS table classes are Tables. Many operations on a MeasurementSet are Table operations. See the Tables module for a list of those operations.

The reason for this class hierarchy is to provide each of the table classes with a separate namespace for its column and keyword enums, so that e.g., they can all have a column named TIME, while sharing as much code as possible. The MSTable class forwards any substantial work to the MSTableImpl class which does the actual work, it is a purely implementation class with static functions not of interest to the user.

Access to columns

To simplify the access of columns, and catch type errors in the column declarations for column access objects (TableColumns) at compile time, there is a helper class for each (sub)table (e.g., MSFieldColumns). The helper class for the MeasurementSet, MSColumns gives access to the main table columns and the helper objects for all subtables.

At present these classes are separate from the Table classes, mainly to ensure that the member functions are only called on valid, completely constructed MeasurementSet Tables. They also represent a large amount of 'state' in the form of TableColumn objects of which only a couple may actually be used.

Units and Measures

Columns in the MeasurementSet and its subtables can have several keywords attached to describe the contents of the column. The UNIT keyword contains an ASCII string describing the unit of the values in the column. The unit member function (in MSTable) will return this unit string, it can be used to construct a Unit object for a particular column.

The MEASURE_TYPE keyword gives the Casacore Measure that applies to the column (if any). See the Measures module for a list of available Measures and their use.

The MEASURE_REFERENCE keyword gives (part of) the reference frame needed to interpret the values in a column. An example is J2000 for the POSITION column. A number of static functions in MeasurementSet are available to create a 'template' Measure for a column, which has the MEASURE_TYPE filled in. Currently the following functions exist: directionMeasure, positionMeasure, epochMeasure and frequencyMeasure. They return a Measure which can then be filled with a value from a particular row from the column to obtain, e.g., a proper MDirection Measure for the phase center.

Reference Tables

Each of the MS classes has a member function referenceCopy which takes the name of a new Table and a list (Block) of column names to create a Table which references all columns in the original table, except for those listed. The listed columns are new columns which can be written to without affecting the original Table. The main use of this is for the synthesis package where corrected and model visibilities are stored as new DATA columns in an MS which references the raw MS for the other columns. Except for these special cases, the use of this function will be rare.

DATA and FLOAT_DATA columns

To accommodate both synthesis and single dish data efficiently, it was decided that a MeasurementSet can have a Complex DATA column, a float FLOAT_DATA column or both. If it has only a FLOAT_DATA column, the corresponding DATA column can be created with the makeComplexData() member function. In special cases, both columns could be present but filled for different rows, with an extra index defined indicating in which column to look (e.g., multi-feed single dish with cross correlations). The details of this last scheme are yet to be worked out. The table consistency checks (isValid()) do not require the presence of either column.

Unset values in MeasurementSet Tables

For ID columns, the rule is that a value of -1 indicates that there is no corresponding subtable in which to look up details. An example is the PULSAR_ID column, which should be set to -1 if the optional PULSAR subtable does not exist.

The rules for non integer unset values in MS tables have not settled down yet. For Floating point and Complex values the recommended practice is to set the values to the FITS and IEEE value NaN, with a bit pattern of all 1's. In much of the present filler code unused values are filled with 0 instead.

Table destruction

Upon destruction, the table and all subtables are checked to see that the MeasurementSet remains valid, i.e., all required columns are present. An exception is thrown if not all required columns are present Nevertheless, the table will be flushed to disk if it is writable - preserving its state.

MS shorthand

While the class name, MeasurementSet, is descriptive, it is often too long for many common uses. The typedef MS is provided as a convenient shorthand for MeasurementSet. The example below uses this typedef.

Example

This example illustrates creation and filling of the MeasurementSet.

// create the table descriptor
TableDesc simpleDesc = MS::requiredTableDesc()
// set up a new table
SetupNewTable newTab("simpleTab", simpleDesc, Table::New);
// create the MeasurementSet
MeasurementSet simpleMS(newTab);
// now we need to define all required subtables
// the following call does this for us if we don't need to
// specify details of Storage Managers or non-standard columns.
simpleMS.createDummySubtables(Table::New);
// fill MeasurementSet via its Table interface
// For example, construct one of the column access objects.
TableColumn feed(simpleMS, MS::columnName(MS::FEED1));
uInt rownr = 0;
// add a row
simpleMS.addRow();
// set the values in that row, e.g. the feed column
feed.putScalar(rownr,1);
// Access the position column in the ANTENNA subtable
ArrayColumn<Double> antpos(simpleMS.antenna(),
MSAntenna::columnName(MSAntenna::POSITION));
// Add a row to it and fill in the position
simpleMS.antenna().addRow();
Array<Double> position(3); 
position(0)=1.; position(1)=2.; position(2)=3.;
antpos.put(0,position);
//.
// For standard columns the above can be done more easily using 
// the MSColumns object.
// Create the MSColumns
MSColumns msc(simpleMS);
// and fill in the position
msc.antenna().position().put(0,position);

Example

This example illustrates read only access to an existing MeasurementSet and creation of an MDirection Measure for the phase center.

// Create the MeasurementSet from an existing Table on disk
MeasurementSet ms("myMS"); 
// Create the RO column access objects for main table and subtables
MSColumns msc(ms);
// show data from row 5
cout << msc.data()(5) << endl;
// show phase center for row 3 in field table
Vector<double> phaseCtr=msc.field().phaseCenter()(3);
cout << phaseCtr<<endl;
// now create a Measure for the phaseCenter
MDirection phaseCenterMeasure =
MS::directionMeasure(msc.field().phaseCenter());
// put the value from row 3 in the Measure and print it
phaseCenterMeasure.set(MVPosition(phaseCtr));
cout <<"phase center:"<< phaseCenterMeasure<<endl;

Motivation

The attempt is to define a single, extensible, Table format that will be able to cope with all, or at least most, radio telescope data. Having a single MeasurementSet should make it easier to combine data from different instruments. The format of the MeasurementSet, table with subtables, was chosen to be able to cope with items varying at different rates more efficiently than a 'flat' Table layout would allow.

To Do

• Incorporate the MSColumn classes in the MeasurementSet classes?
• Variable (row to row) ReferenceFrame (e.g., J2000 mixed with galactic, different Frequency reference frames mixed in the same MS, etc.). This could be done with a column named "column_name"_MEASURE_REFERENCE for each column with varying Measure reference frames.