Subject: Re: draft DID

From: Steven M Beard <[email-masked]>
Date: Wed, 24 Sep 2003 14:59:20 +0100 (BST)

Mike,

> Steven,  Here's the more compact and easier to read FITS version of our
> draft DID.  For each entry we have an expanded dictionary description,
> but for now the summary example FITS header is easier to deal with and
> we propose to iterate to an agreed V0.2 attempt using this.
> 
> If you send your correction/updates we will incorporate as necessary.

Here are my corrections to your current FITS header. It has also occurred
to me that a number of documents in my possession may be useful to you.
Some are attached to this email. I will send the larger ones attached to
separate messages (to avoid cluttering up your email system).

I have attached my "ESO starter" document, which tells a beginner where to
find other relevant ESO-VLT, VISTA and VISTA IR Camera documents. I
compiled the info. for Stewart, but you might find some of it useful.

Corrections/comments are as follows:

* What are the units of RA and DEC fields? Degrees? Hours? Radians?

* Is UTC the UTC at exposure start? There is a requirement for it
  to be possible to derive the absolute UT at mean exposure to within
  0.1s. Can this be done with a combination of UTC and EXPTIME or will
  we need additional information? (At least our exposures are never
  paused).

  What happens if an exposure is cut short using an END command?
  Will there be separate FITS keywords for the originally intended
  exposure time and the actual exposure time? (I presume EXPTIME will
  always contain the actual exposure time).

* What do you mean by "tel jitter pattern" and "microstep pattern"?
  It has occurred to me that we need to make sure we are both using
  a consistent set of definitions. I will send you my "Project glossary"
  document, which contains terms and definitions collected from ESO
  documents and extra ones defined by Gavin and Will.

* INS FILT1 ID1 and INS FILT1 ID2 - these can be replaced by INS FILT1 ID.
  We no longer have a filter ID reading device, so we can make sure each
  filter ID is the same as its official ESO ID - no need to have two
  separate IDs any more.

* I think we also need INS TEMPi UNITS and INS PRESi UNITS fields to
  indicate the units of measurement. I have attached the current proposed
  list of locations for temperature sensors for your information. Some
  of the sensor readings are best reported in 'C' and others in 'K'.

  For the temperature controllers I think we need another keyword

    INS TEMPi TARGET

  to define the target temperature for that location. The keyword

    INS TEMPi VAL

  would then contain the actual measured temperature. (At least I think
  that's how it will work. We need to have a look at the FITS headers of
  other instruments with temperature controllers and see how they do it).

  By the way, I have used the ESO-VLT shorthand "i" to mean "an integer
  starting at 1 and incremented for each unique copy of the thing
  being measured", so TEMPi means TEMP1, TEMP2, TEMP3... etc.

* A trivial point, but the contents of OBS OBSERVER and OBS PI-COI NAME
  is not consistent with OBSERVER and PI-COI. I presume these fields
  will contain identical information?

* Note that the "official" abbreviated name for the VISTA IR Camera
  is "VCAM", so the template names will begin "VCAM_" rather than "VIS_".

* ADA GUID STATUS etc... Three guide stars are required for each
  observation, so you will need separate GUID1, GUID2 and GUID3 keywords.

  How do we distinguish the autoguider stars from the LOWFS stars?
  I think we need to invent another distinguishing keyword such as

    ADA GUID1 DEVICE   'AG'      AG/WFS device associated with star
    ADA GUID2 DEVICE   'LOCS 1'  AG/WFS device associated with star
    ADA GUID3 DEVICE   'LOCS 2'  AG/WFS device associated with star

  It would be interesting to see how OmegaCAM are tacking this problem.

  When the FITS header for a complete "tile" is assembled there will be
  18 associated guide stars. I guess it's up to you how the FITS headers
  of the individual raw "pointings" are combined when you reduce the data.

* As I mentioned at the meeting, the IRACE controller keywords will be
  DET1.

> In parallel with that, as we agreed at the meeting, we will produce an
> actual V0.2 draft DID document containing: an intro, OB context, the
> dictionary, and the example FITS header for the PHDU and the first of the
> SHDUs.

That would be very useful. 

Larger documents to follow...

Cheers,

Steven

==============================================================================
Steven Beard
UK Astronomy Technology Centre
Royal Observatory                  Tel.   : +44 (0)131 668 8253 (direct)
Blackford Hill                              +44 (0)131 668 8100 (switchboard)
Edinburgh EH9 3HJ                  Fax.   : +44 (0)131 668 8314
UK                                 E-mail : [email-masked]

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