FITSSpectralUtil.h

Classes

FITSSpectralUtil -- A class with static functions to help deal with FITS spectral axes. (full description)

class FITSSpectralUtil

Interface

Public Members

static Bool fromFITSHeader(Int &spectralAxis, Double &referenceChannel, Double &referenceFrequency, Double &deltaFrequency, Vector<Double> &frequencies, MFrequency::Types &refFrame, MDoppler::Types &velocityPreference, Double &restFrequency, MDoppler &logger, const RecordInterface &header, char prefix = 'c', Bool oneRelative=True)

static Bool toFITSHeader(String &ctype, Double &crval, Double &cdelt, Double &crpix, Bool &haveAlt, Double &altrval, Double &altrpix, Int &velref, Double &restfreq, LogIO &logger, Double refFrequency, Double refChannel, Double freqIncrement, MFrequency::Types referenceFrame, Bool preferVelocity = True, MDoppler::Types velocityPreference = MDoppler::OPTICAL)

static Bool frameFromTag(MFrequency::Types &referenceFrame, const String &tag, Int velref=-1)

static Bool tagFromFrame(String &tag, Int &velref, MFrequency::Types referenceFrame)

Description

Review Status

Reviewed By:

Eric Sessoms

Date Reviewed:

2002/08/19

Programs:

Tests:

tFITSKeywordUtil.cc

Prerequisite

General knowlege of FITS, FITS keywords, and FITS coordinate conventions is assumed.
Presumably you are using this in conjuction with the FITSKeywordUtil class to get or set the FITS coordinate axis information.

Etymology

This is a collection of static utility functions for use with FITS spectral axes.

Synopsis

This class provides functions to extract information from a FITS header about the spectral axis, to setup a FITS header with appropriate information for the spectral axis, and to translate to and from the MFrequency refrence frame codes and their FITS equivalents. It is never necessary to construct a FITSSpectralUtil, just use the static functions to help handle FITS Spectral axes.

Example

    Record rec;
    ... extract the FITS keyword values into rec using FITSKeywordUtil
    Int whichAxis;
    Double refPix, refFreq, freqInc, restFreq;
    Vector<Double> freqs;
    MFrequency::Types refFrame;
    MDoppler::Types veldef;
    LogIO logger;
    FITSSpectralUtil::fromFITSHeader(whichAxis, refPix, refFreq,
           freqInc, freqs, refFrame, veldef, logger, rec);

Motivation

This is designed to be used after the keywords have been extracted from the FITS file using the FITSKeywordUtil class. Extracting spectral axis and related information requires detailed knowledge of FITS conventions that this class strives to encapsulize.

Member Description

static Bool fromFITSHeader(Int &spectralAxis, Double &referenceChannel, Double &referenceFrequency, Double &deltaFrequency, Vector<Double> &frequencies, MFrequency::Types &refFrame, MDoppler::Types &velocityPreference, Double &restFrequency, MDoppler &logger, const RecordInterface &header, char prefix = 'c', Bool oneRelative=True)

Get information about the spectral axis from a record containing the FITS axis information. Usually this will be from a FITS header using, for example, the FITSKeywordUtil::getKeywords method. referenceFrequency and deltaFrequency give the best possible linear frequency scale. prefix is the first character in the set of keywords describing the axes (e.g. crpix, crval, ctype - the prefix is 'c'). If oneRelative is False, the returned referenceChannel is decrimented from that found in header by 1. The naxis keywords are used to determine the output length of the freqs vector. This method returns False if:

no spectral axis is found. The freqs vector will have a length of zero.

The expected set of axis description keywords is not found.

The spectral axis is FELO but there is no rest frequency (making it impossible to convert to frequency and construct a freqs vector).

The combination FELO and RADIO is used (which does not make sense).

The combination VELO and OPTICAL is used (not yet implemented).

static Bool toFITSHeader(String &ctype, Double &crval, Double &cdelt, Double &crpix, Bool &haveAlt, Double &altrval, Double &altrpix, Int &velref, Double &restfreq, LogIO &logger, Double refFrequency, Double refChannel, Double freqIncrement, MFrequency::Types referenceFrame, Bool preferVelocity = True, MDoppler::Types velocityPreference = MDoppler::OPTICAL)

Nearly the inverse of fromFITSHeader. This returns parameters which could be used in filling in a header record with appropriate values for the spectral axis given the arguments after the logger. The alternate axis description values are set when sufficient information is available. If they have been set, haveAlt will be set to True.

Note that the output arguments after "haveAlt" should not be written to the FITS header unless haveAlt is true.

Note that restfreq is both an input and an output. If there is no rest frequency, set it to be <=0 on input.

If preferVelocity is True, the axis description parameters will be set to those appropriate for a velocity axis given the referenceFrame, and velocityPreference if possible.

This method always returns True.

static Bool frameFromTag(MFrequency::Types &referenceFrame, const String &tag, Int velref=-1)

Convert a reference frame tag (typically found as the characters after the first 4 characters in a ctype string for the frequency-like axis) to a MFrequency::Types value. A velref value (used in AIPS images to alternatively record the velocity reference frame) may also optionally be supplied. If tag is empty, velref will be used if it is >= 0. This function returns False if:

The tag is not empty but is unrecognized.

The tag is empty and velref is unrecognized.

The tag is empty and velref is < 0 (no velref was supplied).

The default value (set when the return value is False) is TOPO.

static Bool tagFromFrame(String &tag, Int &velref, MFrequency::Types referenceFrame)

Construct a reference frame tag from the given referenceFrame An appropriate velref value is also constructed (this may need to be adjusted by +256 if the velocity definition is radio before being used in a FITS file). This returns False if the reference frame is not recognized. The value of tag defaults to "-OBS".