🚀 go-pugleaf

In article <9211101358.AA01257@primate.cv.nrao.edu>, egreisen@primate.CV.NRAO.EDU (Eric Greisen) writes...

	(stuff deleted)

>Again, this is intended to be a convention for celestial coordinates primarily,
>although it suggests a convention that one might wish to use in other areas.
>AIPS will handle any string in CTYPEn, but if that string is not of a recognizable
>type then AIPS will assume that the axis is linear in the coordinate, plot it as
>such, and label it with the value of the CTYPEn string.  It seems to me that this
>is a reasonable compromise ...

Sounds quite reasonable to me too, and addresses my concerns in this area.

Eric Greisen also writes ...

>I applaud the first usage (partly) and deplore the second.  The whole reason for
>having very general and defined keywords was to attempt to convey information
>between sites (and over time) without having to have special codes for every
>2-party connections.  The first usage allows a general program to make some sense
>of the information provides, the second usage simply gets dumped to history files
>and ignored.  The "(partly)" above is from my guess that you could in fact provide
>us with useful celestial coordinate information instead and thereby allow scientists
>to compare your imagery with those generated by other instruments.

Could you clarify what you mean by "first" and "second".  I'm unsure about what
you're getting at here.

In terms of "useful celestial coordinate" information, our plan is to provide
the data in raw units, and in the coordinate system the data was actually taken
in.  The data needed to convert this into useful coordinates and scientific
units will also be included, but not applied.  Our feeling is that the
calibration is a fluid thing, and that our understanding will change over time.
The calibration information stored in the file will probably only represent a
first quess.  We will distribute the calibration data separately, which can be
more easily updated.

Eric Greisen goes on to say ...

>This usage is quite old actually.  It was first described in writing by me in
>April 1983 and has been used on the 1000's of VLA images ever since.  It was picked
>up and used by many other sites over the years and the draft proposal you have
>read was dated in 1988.  I am engaged as we speak in converting the old papers to
>LaTeX so that they can be re-released in a modern form.  I intend also to review
>the proposal and flesh it out with better details. ...

By "new", I mean that it is not discussed within the confines of the FITS
standard document.  I'm surprised that you decided to add new functionality
within a pre-existing structure.  Future enhancements to the standard should
avoid this trap.

Bill Thompson