Subject: GBT use of FITS for single dish data

From: [email-masked] (Bob Payne)
Date: Fri, 17 Mar 1995 08:38:58 -0500

We would not have decided to use FITS for GBT data collection if the
multidimensional array and variable length array conventions were not
available and supported. The libraries I use, "fitsio" for fortran and
IDL astronomy library for PV-WAVE all support this convention.

I note that Ray Norris
>Another related problem is the use of arrays of different lengths,
>which others (e.g. Bob) have already noted. Typically in multi-band
>observations you might observe with different numbers of channels in
>each band, and different bandwidths, to achieve comparable velocity 
>resolution. So I for one would urge that we try to incorporate 
>support for variable length arrays.

and Phil Jewell

>Also, Phil Jewell has suggested via e-mail that continuum data may be
>a prime example where variable length arrays are extremely useful.

and the GBT all reccommend use of the variable length array
convention.

Consequently I do not see the point of Bob Garwood's recommendation
against variable length arrays.

>My inclination is that the SD-FITS standard echo the
>recommendation against variable length arrays from the FITS binary
>table standard but recognize that there are situations where it will
>be used.

For the GBT we plan on using the simplest FITS format appropriate
for the data. Most table data such as weather station data and even
continuum backend data will be stored in binary tables with scaler
data values. More complex backends such as the spectral processor
require data values which are multidimensional. While not currently
used in that mode the spectral processor is capable of generating
variable length data arrays.

I suggest that the SD-FITS standard recognize the use of the
variable length array convention and drop all recommendations against
its use.

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From: [email-masked] (Bob Garwood)
Date: Fri, 17 Mar 1995 08:59:15 +0500

> variable length array convention and drop all recommendations against

In an earlier note to dishfits (on Mar 2) I wrote:

"I've come to the conclusion that we simply can't ignore the proposed
variable length array convention and we should allow for it in 
this convention."

So I'm pretty sure we're all in agreement on this one already.

-Bob

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From: [email-masked] (Ray Norris)
Date: Thu, 23 Mar 95 17:42:12 EST

Regarding Barry's comment:

> This requirement also makes it possible to construct utility programs 
> that dump all the headers in a FITS file without reading the data.
> After reading one header, they use the information in it to skip to
> the next. Such software is a very useful tool for examining newly
> received files.

Yes, but it's also trivial to write utility programs, and FITS readers,
that just check the first few bytes of each FITS block to see if it's
any sort of header (we do this in RPFITS). So although this standard
does indeed violate the original FITS standard, maybe it's time to
re-examine that standard.

Cheers

Ray