Subject: Re: Testing of BINTABLE and IMAGE extensions

From: [email-masked] (William Pence)
Date: Fri, 22 Oct 93 17:22:29 EDT

Dear IAU-FWG members,

I have examined the test FITS files recently provided by Preben Grosbol
and have produced ASCII listing of the file contents using our FTOOLS
package.  My tests were performed on a SUN SPARCstation IPC.  In
principle I can run the same software on a VAX or an Ultrix DECstation,
but have not attempted this due to a lack of time.

The file listings for test files 9-12 and 14 are available for others
to compare and are located in the anonymous ftp account on
tetra.gsfc.nasa.gov (128.183.8.77) in the /pub/test subdirectory.

A few comments about these test files:

1.   I could not easily display the scaled values for column 3 of the ASCII tables
(in test files 9 and 11), therefore I just give the unscaled values in the listings.

2.  In the IMAGE extentions, I only display the first 12 columns of the first plane of 
the data cube, to reduce the size of the file listing.

3.   There appears to be a slight problem in the BINTABLE extentions of test files 10
and 12 in that the TFORM keyword for column 10 is:

TFORM10 = 'PI(13)  '           / Max. length is 13 16-bit values

but there are in fact many more than 13 elements in many of the rows of
the table (according to my software).  From my interpretation of the BINTABLE
definition document, this is not allowed.  But in any case, my software
ignores the MAXLEN value given in the TFORM keyword and returns the
actual number of elements defined for each row.

4.  My software is not currently capable of handling the UNKNOWN
special records following the BINTABLE in test file no. 12.  It treats
any unrecognized bytes following a valid extension as an end-of-file
indicator.  This is done because on VAX/VMS systems one often gets some
padding bytes at the end of a FITS file if the file does not have an
intrinsic 2880-byte block size (512-byte blocked FITS files are quite
common).

5.  I've provided 2 listings for the test file number 14.  The file
tst0014a.lis displays the raw data values in the table, at full numeric
precision, whereas the tst0014b.lis file displays each column using the
display format specified by the TDISPn keyword.

Regards,
Bill Pence

---

From: [email-masked]
Date: Mon, 25 Oct 93 15:17:42 +0100

Dear IAU-FWG members,
 I am very pleased to that W.Pence has started the 
test/verification  of the extension and hope that
others will join soon. 

 The data values in the listings I can in general 
confirm with the following comments:

 1) The listing of of the ASCII table in tst0009.mt
    gives the ASCII contence of the columns, not the
    user values after applying format and scaling eg.
    in column 2, 4 and 5.

 2) I rechecked the BINTABLE extension which was
    written by hand. Actually, I had swapped the
    length and offset in column 10 'PI(13)'. The
    error is now corrected and the new files placed
    on the ftp account.

 3) The UNKNONW extension in file tst0012.mt should
    conform the the general rules. It has a nice
    FITS header:
       XTENSION= 'XZQ-EXTN'           / Non-standard extension
       BITPIX  =                    8 / Data are in bytes
       NAXIS   =                   13 / A total of 13 axes !!!
       NAXIS1  =                   17 / Pixels in this axis
       NAXIS2  =                   41 / Pixels in this axis
       NAXIS3  =                    1 / Pixels in this axis
       NAXIS4  =                    1 / Pixels in this axis
       NAXIS5  =                    1 / Pixels in this axis
       NAXIS6  =                    1 / Pixels in this axis
       NAXIS7  =                    1 / Pixels in this axis
       NAXIS8  =                    1 / Pixels in this axis
       NAXIS9  =                    1 / Pixels in this axis 
       NAXIS10 =                    1 / Pixels in this axis
       NAXIS11 =                    1 / Pixels in this axis
       NAXIS12 =                    1 / Pixels in this axis
       NAXIS13 =                    2 / Pixels in this axis
       PCOUNT  =                  553 / Parameter values per group
       GCOUNT  =                    3 / No. of groups
       ...
       END
    It is given to check if readers can skip unknown extension and
    decode the ones after it. A reader should normally check it
    the string 'XTENSION' is present after an extension.

Although it is not a part of the BINTABLE proposal we may have to
discuss the wording in App. B on the P-format. The action when
length or pointer is off limits should be specified.

Best regards
Preben

PS: Any one who want a QIC tape for an exchange test?