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Re: Coding of floating values in MIDAS BDF files in VAX/VMS and AXP/VMS

Bernard Debray wrote:

> Warning: data is VAX Float instead of Gfloat...
> frame: WD_MRK691_1_202  (data = R4)
> NAXIS:                    1
> NPIX:                   571
> START:               0.26897961173593E+32
> STEP:                 2048.0000000000
> IDENT:           WD_MRK691_1_202
> CUNIT:           none given
> LHCUTS:            -7.046526       162.8535      -7.046526     162.8535
> so the values in START and STEP are totally meaningless.

The comment I am about to make may appear a bit like the one librarians
fear - the reader who comes into the library asking for help to find a
book that they've seen before, but they can't remember the title or the
author --- but it is green.

As you say, START and STEP are double precision descriptors---or should
be.  I did some years ago come across some MIDAS procedure somewhere
---and this is where I am like the clueless reader in the library, but
it may have been in the echelle spectroscopy package---where these
descriptors were incorrectly treated as single precision.  (I do
believe/hope I reported this fault.)  Your user wrote
the images in 1992:  you should perhaps keep in mind the possibility
that the descriptors were written wrongly (and presumably within the
version of MIDAS/package used at the time also read wrongly but
consistently) and that there is nothing wrong with the decoding under

There might be some way you could test this hypothesis by copying
START and STEP into single precision descriptors and seeing if they are
then correct...

Best wishes,
William Tobin.
* Dr William TOBIN, Department of Physics & Astronomy, University of *
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