[fitsbits] fitsverify and "implied" table columns themselves...?

[William Pence]

The new FITS Standard document, in table 8.2, defines the keyword naming 
convention (taken from the WCS papers) that one should use if the image 
is stored as a multidimensional vector in a binary table column. (See 
http://fits.gsfc.nasa.gov/standard30/htmlfiles/fits_standard30index.html 
page 77).

Here are some examples, where 'i' is the axis number, 'n' is the column 
number that contains the image, and 'a' is the optional alternate axis 
label from A to Z):

   Primary Array       Bintable vector
   -------------       ---------------
    CTYPEia             iCTYPn or iCTYna
    CRVALia             iCRVLn or iCRVna
    CDELTia             iCDLTn or iCDEna

-Bill

Bob Garwood wrote:
> That appears to be the SDFITS convention, which predates the WCS papers 
> and agreements.  The WCS information in those tables is unlikely to be 
> widely understood as a result.  The SDFITS convention needs to be 
> updated to take into account the accepted ways of conveying WCS 
> information in binary tables.  If the DATA array column dominates the 
> table size, then I suspect adding a few extra scalar columns won't 
> greatly increase the table size.
> 
> -Bob
> 
> Mike Nolan wrote:
>> We're writing radio data in binary tables, and fitsverify hates them:
>>
>> (nolan at mofongo.naic.edu 133) fitsverify /share/pdata1/pdev/x108.20080826.b0s1g0.
>> 00800.fits
>>  
>>               fitsverify 4.13 (CFITSIO V3.090)              
>>               --------------------------------              
>>  
>>  
>> File: /share/pdata1/pdev/x108.20080826.b0s1g0.00800.fits
>>
>> 2 Header-Data Units in this file.
>>  
>> =================== HDU 1: Primary Array ===================
>>  
>>  16 header keywords
>>  
>>  Null data array; NAXIS = 0 
>>  
>> =================== HDU 2: BINARY Table ====================
>>  
>> *** Error:   Keyword #29, CTYPE1 is not allowed in the Bin/ASCII table.
>> *** Error:   Keyword #31, CTYPE2 is not allowed in the Bin/ASCII table.
>> *** Error:   Keyword #44, CTYPE2G is not allowed in the Bin/ASCII table.
>> ... many more similar errors
>>
>> Some of the WCS parameters are table columns:
>> COMMENT  axis 1 is the frequency axis
>> TTYPE6  = 'CRVAL1  '           / Center frequency
>> TFORM6  = '1D      '           /
>> TUNIT6  = 'Hz      '           /
>> TDISP6  = 'D13.5   '           /
>> TTYPE7  = 'CDELT1  '           / Frequency interval
>> TFORM7  = '1D      '           /
>> TUNIT7  = 'Hz      '           /
>> TDISP7  = 'D13.5   '           /
>> TTYPE8  = 'CRPIX1  '           / Pixel of center frequency
>> TFORM8  = '1D      '           /
>> TUNIT8  = '        '           /
>> TDISP8  = 'D13.5   '           /
>>
>> but others are constant, so we're putting them in the table header
>> per the "Green Bank Convention". 
>> CTYPE1  = 'FREQ    '           / Type of coordinate
>> CUNIT1  = 'Hz      '           / Unit of center frequency
>>
>> These files are massive and written at 80 MB/s, so we really don't want to make them any bigger than they have to be.
>>
>> Does that really make us bad people? Or have I missed something?
>>
>> Thanks,
>>
>> -Mike
>>
>>
>>   
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-- 
____________________________________________________________________
Dr. William Pence                       William.Pence at nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)