VLASDA Class Reference

Interprets the data in an sub-array data area of a VLA logical record. More...

#include <VLASDA.h>

List of all members.

Public Member Functions
	VLASDA ()
	The default constructor creates a unusable object.
	VLASDA (ByteSource &record, uInt offset)
	Construct this object to read data from the SDA of the given VLA logical record.
	~VLASDA ()
	The destructor is trivial;.
	VLASDA (const VLASDA &other)
	The copy constructor uses reference semantics.
VLASDA &	operator= (const VLASDA &other)
	The assignment constructor uses reference semantics.
void	attach (ByteSource &record, uInt offset)
	Re-initialise this object so that it now reads data from the given VLA logical record.
uInt	trueChannels (VLAEnum::CDA cda) const
	returns the number of data channels in the specified CDA (including the average channel)
uInt	nChannels (VLAEnum::CDA cda) const
	returns the number of spectral channels in the specified CDA (excludes channel zero)
Double	obsFrequency (VLAEnum::CDA cda) const
	returns the observed frequency (in Hz), at the band centre for the specified CDA.
Double	edgeFrequency (VLAEnum::CDA cda) const
	returns the observed frequency at the lower edge of the band, after correcting for channels that have been correlated and discarded prior to archiving the data.
Bool	dopplerTracking (VLAEnum::CDA cda) const
	returns true if Doppler tracking has been turned on for the specified CDA.
Double	restFrequency (VLAEnum::CDA cda) const
	returns the assumed rest frequency of the source radiation in Hz (for the specified CDA).
Double	radialVelocity (VLAEnum::CDA cda) const
	returns the assumed radial velocity of the source in m/sec (for the specified CDA).
MFrequency::Types	restFrame (VLAEnum::CDA cda) const
	Return the assumed rest frame that will be used when calculating the observers motion relative to the source (for the specified CDA).
MDoppler::Types	dopplerDefn (VLAEnum::CDA cda) const
	Return the definition of Doppler shift used to convert the radial velocity to a frequency (for the specified CDA).
Double	channelWidth (VLAEnum::CDA cda) const
	returns the bandwidth of an individual channel, in Hz, of the data in the specified CDA.
Double	correlatedBandwidth (VLAEnum::CDA cda) const
	returns the total bandwidth, in Hz, over all the channels of the data in the specified CDA.
Double	filterBandwidth (VLAEnum::CDA cda) const
	returns the total bandwidth, in Hz, of the front end filter in the specified CDA.
VLAEnum::CorrMode	correlatorMode () const
	Return the correlator mode for this record.
uInt	electronicPath (VLAEnum::CDA cda) const
	Return the 'electronic path' that the data in the specified CDA has travveled through.
uInt	npol (VLAEnum::CDA cda) const
	Return the number of polarisations in the specified CDA.
Matrix< VLAEnum::IF >	ifUsage (VLAEnum::CDA cda) const
	return a Matrix indicating which if's contributed to which correlations within the specified CDA.
uInt	subArray () const
	Return the subarray ID.
String	arrayConfig () const
	Return the Array configuration as a string.
Vector< Double >	sourceDir () const
	Return the source RA and Dec at the standard epoch of this integration (given by the epoch function).
String	sourceName () const
	Return the source name as typed in by the observer.
Int	sourceQual () const
	Return the source qualifier as typed in by the observer.
Double	intTime () const
	Return the integration time in seconds.
Double	obsTime () const
	Return the observation time in seconds of the centre of this integration.
String	obsId () const
	Return the observation program id.
String	obsMode () const
	Return the observing mode.
String	obsModeFull () const
	Return the observing mode in full glory.
String	calCode () const
	Return the calibration code.
MDirection::Types	epoch () const
	return the reference frame for the field directions.
Bool	smoothed () const
	returns whether the data spectrum has been Hanning smoothed (and every second channel discarded).
Private Attributes
ByteSource	itsRecord
uInt	itsOffset
	the offset to the start of this SDA in the record.

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Detailed Description

Interprets the data in an sub-array data area of a VLA logical record.

Intended use:

Public interface

Review Status

Date Reviewed:

yyyy/mm/dd

Prerequisite

• The VLA archive format as described in VLA computer memo 188

Etymology

The sub-array data is, in memo 188, frequently shortened to the acronym SDA. As this is specific to the VLA the name VLAADA seemed appropriate.

Synopsis

This class contains functions which access and interpret the data in the sub-array data area of a VLA logical record.

The functions in this class access the specified data in the sub-array data area and may convert the units and data types to something more suitable for general use. They also interpret the data and provide some derived quantities eg., the nPol function.

Example

This code fragment shows how to initialise a VLASDA object and then use this object to determine how much data is in this record. It is assumed that the Bytesource object contains a VLA Logical record.

      ByteSource VLARecord(...);
      VLARCA rca;
      VLASDA sda(VLARecord, rca.SDAOffset());
      cout << "The record has " << rca.nAntennas() <<  " antennas." << endl;
      for (uInt c = 0; c < 4; c++) {
          cout << "CDA " << c;
        if (rca.CDAOffset() == 0) {
          cout << " is not used." << endl;
        else {
          cout << " has " << sda.nChannels(c) << " spectral channels and"
               << sda.npol(c) << " polarisations." << endl;
        }
      }

Motivation

This class was needed as part of the VLA filler application.

Thrown Exceptions

class will throw an exception (AipSError) if you the correlator data area argument is four or more. When compiled in debug mode this class does a lot of consistancy checking. If it detects anomolies it will throw an exception (AipsError).

To Do

• The member functions should probably be rounded out.

Definition at line 113 of file VLASDA.h.

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Constructor & Destructor Documentation

VLASDA::VLASDA

(

)

The default constructor creates a unusable object.

You need to use the assignment operator or the attach function to create a usable object.

VLASDA::VLASDA	(	ByteSource &	record,
		uInt	offset
	)

Construct this object to read data from the SDA of the given VLA logical record.

The SDA must begin at the specified number of bytes from the beginning of the record (see the example above).

VLASDA::~VLASDA

(

)

The destructor is trivial;.

VLASDA::VLASDA

(

const VLASDA &

other

)

The copy constructor uses reference semantics.

---

Member Function Documentation

String VLASDA::arrayConfig

(

)

const

Return the Array configuration as a string.

The string will contain at between one and two characters and be somethings like "A", "D", "AD", etc

void VLASDA::attach	(	ByteSource &	record,
		uInt	offset
	)

Re-initialise this object so that it now reads data from the given VLA logical record.

The sub-array data area that will be used begins at the specified number of bytes from the beginning of the record.

String VLASDA::calCode

(

)

const

Return the calibration code.

Double VLASDA::channelWidth

(

VLAEnum::CDA

cda

)

const

returns the bandwidth of an individual channel, in Hz, of the data in the specified CDA.

Double VLASDA::correlatedBandwidth

(

VLAEnum::CDA

cda

)

const

returns the total bandwidth, in Hz, over all the channels of the data in the specified CDA.

Throws an exception if which > 3.

VLAEnum::CorrMode VLASDA::correlatorMode

(

)

const

Return the correlator mode for this record.

Only useful if you know what these codes are. The functions immediatly following this one are probably more useful as they interpret this code for you.

MDoppler::Types VLASDA::dopplerDefn

(

VLAEnum::CDA

cda

)

const

Return the definition of Doppler shift used to convert the radial velocity to a frequency (for the specified CDA).

This is supplied by the observer and used in the Doppler tracking calculations. The returned value is not meaningful of Doppler tracking is not used.

Bool VLASDA::dopplerTracking

(

VLAEnum::CDA

cda

)

const

returns true if Doppler tracking has been turned on for the specified CDA.

If so then the observed frequency is calculated from the source radial velocity, the line rest frequency and the component of the earths velocity relative to the source (in the specified reference Frame).

Double VLASDA::edgeFrequency

(

VLAEnum::CDA

cda

)

const

returns the observed frequency at the lower edge of the band, after correcting for channels that have been correlated and discarded prior to archiving the data.

ie it returns the observed frequency of the lower edge of the first channel in the data.

uInt VLASDA::electronicPath

(

VLAEnum::CDA

cda

)

const

Return the 'electronic path' that the data in the specified CDA has travveled through.

Returns 0 if the data in the specified CDA is from IF's A or C and 1 if the data is from IF's B or D. The returned value is meaningless if the CDA is not used in the current record. This information is obtained from knowing what the correlator modes represent.

MDirection::Types VLASDA::epoch

(

)

const

return the reference frame for the field directions.

Double VLASDA::filterBandwidth

(

VLAEnum::CDA

cda

)

const

returns the total bandwidth, in Hz, of the front end filter in the specified CDA.

Throws an exception if which > 3.

Matrix<VLAEnum::IF> VLASDA::ifUsage

(

VLAEnum::CDA

cda

)

const

return a Matrix indicating which if's contributed to which correlations within the specified CDA.

The return Matrix always has two columns and the same number of rows as there are correlations. Each row indicates which IF from antennas one & two respectrively contributed to thw correlation. This function encodes the information in Appendix F1 of memo 188.

Double VLASDA::intTime

(

)

const

Return the integration time in seconds.

uInt VLASDA::nChannels

(

VLAEnum::CDA

cda

)

const

returns the number of spectral channels in the specified CDA (excludes channel zero)

uInt VLASDA::npol

(

VLAEnum::CDA

cda

)

const

Return the number of polarisations in the specified CDA.

This information is obtained from knowing what the correlator modes represent.

Double VLASDA::obsFrequency

(

VLAEnum::CDA

cda

)

const

returns the observed frequency (in Hz), at the band centre for the specified CDA.

This is the observed frequency after Doppler tracking has been applied. It will correspond to the middle of the centre channel if there are an odd number of channels and takes into account that some channels may have been correlated but discarded prior to archiving.

String VLASDA::obsId

(

)

const

Return the observation program id.

String VLASDA::obsMode

(

)

const

Return the observing mode.

String VLASDA::obsModeFull

(

)

const

Return the observing mode in full glory.

Double VLASDA::obsTime

(

)

const

Return the observation time in seconds of the centre of this integration.

Zero seconds means midnight on the day specified win the RCA.

VLASDA& VLASDA::operator=

(

const VLASDA &

other

)

The assignment constructor uses reference semantics.

Double VLASDA::radialVelocity

(

VLAEnum::CDA

cda

)

const

returns the assumed radial velocity of the source in m/sec (for the specified CDA).

This number is supplied by the observer and used in the doppler tracking calculations. The returned value is not meaningful if doppler tracking is not used.

MFrequency::Types VLASDA::restFrame

(

VLAEnum::CDA

cda

)

const

Return the assumed rest frame that will be used when calculating the observers motion relative to the source (for the specified CDA).

This frame is supplied by the observer and used in the Doppler tracking calculations. The returned value is not meaningful of Doppler tracking is not used.

Double VLASDA::restFrequency

(

VLAEnum::CDA

cda

)

const

returns the assumed rest frequency of the source radiation in Hz (for the specified CDA).

This number is supplied by the observer and used in the doppler tracking calculations. The returned value is not meaningful if doppler tracking is not used.

Bool VLASDA::smoothed

(

)

const

returns whether the data spectrum has been Hanning smoothed (and every second channel discarded).

Always returns False for continuum data.

Vector<Double> VLASDA::sourceDir

(

)

const

Return the source RA and Dec at the standard epoch of this integration (given by the epoch function).

The returned Vector will always have two elements being the RA and Dec in radians.

String VLASDA::sourceName

(

)

const

Return the source name as typed in by the observer.

Int VLASDA::sourceQual

(

)

const

Return the source qualifier as typed in by the observer.

This is really the scan number.

uInt VLASDA::subArray

(

)

const

Return the subarray ID.

This is a number between 1 and 4 indicating which subarray this data corresponds to.

uInt VLASDA::trueChannels

(

VLAEnum::CDA

cda

)

const

returns the number of data channels in the specified CDA (including the average channel)

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Member Data Documentation

uInt VLASDA::itsOffset [private]

the offset to the start of this SDA in the record.

An offset of zero means this SDA is not used in this record.

Definition at line 278 of file VLASDA.h.

ByteSource VLASDA::itsRecord [mutable, private]

Definition at line 275 of file VLASDA.h.

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

• code/nrao/VLA/VLASDA.h