From timmyd at netcom.com  Tue May  7 10:20:41 1996
From: timmyd at netcom.com (Tim DeBenedictis)
Date: 7 May 1996 14:20:41 GMT
Subject: Std. date/time/RA/Dec FITS keywords?
Message-ID: <4mnm7n$pf@pecos.msfc.nasa.gov>

Greetings all-

I am writing some astrometry software which needs to run with a variety 
of different FITS-format images.  It would be nice to use the R.A., Dec., 
date, and time information stored in the images' FITS headers, but 
unfortunately there does not seem to be any standard FITS keywords which 
provide this information.

I read the defining FITS paper, which describes the DATE-OBS keyword; 
however, there is no corresponding TIME-OBS keyword, and one-day time 
resolution is not sufficient.

I also read about the CRVAL, CRPIX, CRDEL, and CROT keywords, which sem 
to specify the coordinates, rotation, and image scale.  However, as far 
as I can tell, no one actually seems to use these in practice!  I've 
worked with a variety of images from institutions like Kitt Peak, Lowell 
Observatory, as well as amateur images from SBIG cameras.  The only thing 
I've seen is keywords like RA and DEC which then list an R.A. and Dec. in 
hours/minutes/seconds as an ASCII string.

Is there any standard way of handling these things?  What is the 
"correct" way to do it?  Please send e-mail, as I am not able to check 
responses to all the groups I've posted this to.

-Tim DeBenedictis
timmyd at netcom.com



From psb at ast.cam.ac.uk  Thu May  9 12:20:44 1996
From: psb at ast.cam.ac.uk (Peter Bunclark)
Date: 9 May 1996 16:20:44 GMT
Subject: Std. date/time/RA/Dec FITS keywords?
Message-ID: <4mt60p$1pn@pecos.msfc.nasa.gov>

Tim DeBenedictis wrote:
> 
> Greetings all-
> 
> I am writing some astrometry software which needs to run with a variety
> of different FITS-format images.  It would be nice to use the R.A., Dec.,
> date, and time information stored in the images' FITS headers, but
> unfortunately there does not seem to be any standard FITS keywords which
> provide this information...[deletia - mod.]

Read :
<A HREF="http://fits.cv.nrao.edu/documents/documents.html" >FITS
Documents</A>

[moral: check the 'net before pressing "post" - mod.]



From sla at umbra.ucolick.org  Mon May 13 10:36:56 1996
From: sla at umbra.ucolick.org (Steve Allen)
Date: 13 May 1996 14:36:56 GMT
Subject: Std. date/time/RA/Dec FITS keywords?
Message-ID: <4n7he5$3m8@pecos.msfc.nasa.gov>

In article <4mt60p$1pn at pecos.msfc.nasa.gov>,
Peter Bunclark  <psb at ast.cam.ac.uk> wrote:
>Tim DeBenedictis wrote:
>> of different FITS-format images.  It would be nice to use the R.A., Dec.,
>> date, and time information stored in the images' FITS headers, but
>> unfortunately there does not seem to be any standard FITS keywords which
>> provide this information...[deletia - mod.]

>Read :
><A HREF="http://fits.cv.nrao.edu/documents/documents.html" >FITS
>Documents</A>

This reply may give the impression that there is a definitive answer
to the question.  There is not.

There are no adopted standards specifying the keyword name or format
of RA and Dec in a FITS header.  There exists decimal degrees, decimal
hours, and hexadecimal strings in hours and degrees.  The given RA and
Dec may be expressed in a catalog reference frame or as notably
inaccurate telescope encoder readings.

Similarly there is no adopted standard specifying the keyword name or
format of observation time in a FITS header.  Again, existing practice
varies rather widely as do the accuracies of the clocks used to obtain
the time.

There is a draft document at
http://fits.cv.nrao.edu/documents/wcs/wcs.html
whose adoption should solve this problem, but its recommendations
are not generally found in any existing FITS headers.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 408 459 3046     FAX: +1 408 454 9863
WWW: http://www.ucolick.org/~sla                PGP public keys:  see WWW



From psb at ast.cam.ac.uk  Tue May 14 03:46:58 1996
From: psb at ast.cam.ac.uk (Peter Bunclark)
Date: Tue, 14 May 1996 08:46:58 +0100
Subject: Std. date/time/RA/Dec FITS keywords?
References: <4n7he5$3m8@pecos.msfc.nasa.gov>
Message-ID: <31983A72.2310@ast.cam.ac.uk>

Steve Allen wrote:
> 
> In article <4mt60p$1pn at pecos.msfc.nasa.gov>,
> Peter Bunclark  <psb at ast.cam.ac.uk> wrote:
> >Tim DeBenedictis wrote:
> >> of different FITS-format images.  It would be nice to use the R.A., Dec.,
> >> date, and time information stored in the images' FITS headers, but
> >> unfortunately there does not seem to be any standard FITS keywords which
> >> provide this information...[deletia - mod.]
> 
> >Read :
> ><A HREF="http://fits.cv.nrao.edu/documents/documents.html" >FITS
> >Documents</A>
> 
> This reply may give the impression that there is a definitive answer
> to the question.  There is not.
> 
> There are no adopted standards specifying the keyword name or format
> of RA and Dec in a FITS header.  There exists decimal degrees, decimal
> hours, and hexadecimal strings in hours and degrees.  The given RA and
> Dec may be expressed in a catalog reference frame or as notably
> inaccurate telescope encoder readings.
> 
> Similarly there is no adopted standard specifying the keyword name or
> format of observation time in a FITS header.  Again, existing practice
> varies rather widely as do the accuracies of the clocks used to obtain
> the time.
> 
> There is a draft document at
> http://fits.cv.nrao.edu/documents/wcs/wcs.html
> whose adoption should solve this problem, but its recommendations
> are not generally found in any existing FITS headers.
> 
> --
> Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
> sla at ucolick.org      Voice: +1 408 459 3046     FAX: +1 408 454 9863
> WWW: http://www.ucolick.org/~sla                PGP public keys:  see WWW

I agree that there hasn't been much standardisation up to present; but
anyone writing new software should study the available documents on
wcs, including the section in NASA's ``A Users's Guide for the Flexible
Image Transport System (FITS)'',  and apply the recomendations to his
instrument/system.
	The disagreements seem to be in how exactly to represent the
image skew, rotation and scale.  The actual convention for representing
the coordinates of the reference pixel are as laid down in the
mystical PAPER I , ie CRVALn in degrees for ra and dec.  Meanwhile,
most observatories have actually used RA and DEC keywords in more or 
less human-readable format, but these shouldn't in fact be part of
a wcs.
	Since widely-distributed software (eg SAOTNG) is becoming available
to exploit images with wcs, there is much more motivation than
previously to exploit the potential.

Peter.



From rlm at astro.physics.uiowa.edu  Thu May 16 20:02:48 1996
From: rlm at astro.physics.uiowa.edu (Robert Mutel)
Date: Fri, 17 May 1996 00:02:48 GMT
Subject: Std. date/time/RA/Dec FITS keywords?
References: <4n7he5$3m8@pecos.msfc.nasa.gov>
Message-ID: <319BC228.1E5A@astro.physics.uiowa.edu>

Readers of sci.astro.research may be interested in a collection of programs for FITS images called ATFtools.
It includes a tool for inserting world coordinates into a FITS image header by pattern matching to the 
Guide Star Catalog. The program (wcs) uses the nominal ra, dec, keywords (along with keyword crpix for
plate scale) to roughly locate the image center and either an online or CD-ROM GSC database to do the pattern
matching. The programs have been ported to several UNIX systems (Linux, Solaris, Unixware) and Windows-95. 
There are also tools for batch photometry, FITS  header editing, and multiple image alignment. and cropping.

The Windows-95 port is available at
<a href="http://www-astro.physics.uiowa.edu/atf_atftools.html>ATFtools</a>

The UNIX port will be available for ftp access in early June.


Robert Mutel
Department of Physics and Astronomy
University of Iowa, Iowa City IA 52242
Telephone: 319-335-1950      FAX: 319-335-1753
Email: rlm at astro.physics.uiowa.edu

Steve Allen wrote:
> 
> In article <4mt60p$1pn at pecos.msfc.nasa.gov>,
> Peter Bunclark  <psb at ast.cam.ac.uk> wrote:
> >Tim DeBenedictis wrote:
> >> of different FITS-format images.  It would be nice to use the R.A., Dec.,
> >> date, and time information stored in the images' FITS headers, but
> >> unfortunately there does not seem to be any standard FITS keywords which
> >> provide this information...[deletia - mod.]




From bschlesinger at nssdca.gsfc.nasa.gov  Thu May 30 16:58:00 1996
From: bschlesinger at nssdca.gsfc.nasa.gov (Barry M. Schlesinger)
Date: 30 May 1996 16:58 EDT
Subject: Sources of FITS Information
Message-ID: <30MAY199616584453@nssdca.gsfc.nasa.gov>

Archive-name: astronomy/fits/info-sources
Last-modified: 1996/04/22

--------
		Sources of FITS Information 

Preface 	

This material on sources of Flexible Image Transport System (FITS)
information is posted and updated periodically by the FITS Support
Office at the NASA Goddard Space Flight Center (GSFC).  It discusses
where general FITS information, including some answers to frequently
asked questions, can be found, and provides sources for detailed
information on FITS software and documentation. 

-------

FITS Support Office

The FITS Support Office maintains a library of FITS information
accessible from http://ssdoo.gsfc.nasa.gov/astro/fits/fits_home.html or
ftp://nssdc.gsfc.nasa.gov/pub/fits/.  The material available includes

o	"Definition of FITS," a codification of FITS for the 
	NASA/Science Office of Standards and Technology (NOST),
	available in LaTeX, uncompressed PostScript, compressed 
	PostScript and (usually) ASCII text
	(The ASCII text version may not be available for a short 
	while after the announcement of a new version.)

o	"A User's Guide to FITS", published by the FITS Support Office, 
	in LaTeX, and compressed and uncompressed PostScript 

o	Revisions to version 1.0 of the "Definition of FITS" covering the
	specification of units that were incorporated 
	into version 1.1 (text)

o	A current list of the extension type (structure) names
	registered with the International Astronomical Union FITS
	Working Group (IAUFWG) (text)

o	Rules for physical blocking on various media adopted by
	the IAUFWG (text)  

In the same directory, but accessible directly via 
http://ssdoo.gsfc.nasa.gov/astro/fits/basics_info.html is the FITS
Basics and Information that used to be regularly posted to
sci.astro.fits and sci.data.formats.  It continues to be revised to
reflect current FITS developments.  It contains the following material: 

o	An overview of FITS

o	A list of FITS documents  

o	A list of software packages that support FITS, 
		including FITS-image converters for various platforms

o	A list of on-line FITS resources

o	A description of the FITS Support Office 

The hypertext version provides links to many of the documents, 
software, and network locations listed.  The text version provides 
information on how to obtain much of this material.

There is also a hypertext version of the List of Registered 
Extensions.

Links from the Web page and subdirectories of the ftp directory 
contain
	
o	Software developed by the FITS Support Office.  

o	Error test files, primary HDUs useful for testing the ability
	of software designed to read FITS files to cope with files that 
	have errors or are non-standard.  These files should be 
	downloaded in binary form.

Printed copies of the material in the FITS directory can be obtained
from the Coordinated Request and User Support Office (CRUSO):  

(Postal) Coordinated Request and User Support Office
         Code 633
	 National Space Science Data Center
	 NASA Goddard Space Flight Center
	 Greenbelt MD 20771 USA

(Electronic mail) request at nssdca.gsfc.nasa.gov

(Telephone)  +1-301-286-6695 8:00 A. M. - 4:30 P.M. U. S. Eastern Time
(-0500 from the last Sunday in October through the first Saturday in
April; -0400 the remainder of the year) 
	When no one is available, messages can be left on voice mail. 
(FAX) +1-301-286-1635

-------

National Radio Astronomy Observatory (NRAO)

A FITS Archive can be found at URL http://fits.cv.nrao.edu/ or 
at ftp://fits.cv.nrao.edu/fits, located at NRAO.  This machine supports a
WAIS server named nrao-fits which has an index of all of the
FITS-related text files in the archive; the file nrao-fits.src is
available at think.com and at
ftp://fits.cv.nrao.edu/fits/wais-sources/nrao-fits.src.  

Some of the more noteworthy materials in this archive are 

o	Drafts of proposed additions to the FITS standard and other 
	drafts that may in the future be formally proposed

o	Text of any detailed proposals currently being discussed by 
	the FITS committees

o	A collection of documents on World Coordinate Systems, 
	including the current draft proposal

o	Conventions specific to particular projects or disciplines

o	Software packages for display of FITS images on Windows 3.1,
	Windows 95, Macintosh, and Unix/X-Windows

o 	Other code for various environments and Usenet postings about
	code 

o	Sample data and special test files designed to measure the
        ability of a FITS reader to handle a wide variety of FITS files

o	Archives of traffic on FITS-related newsgroups and exploders

-------

HEASARC
	The NASA/Goddard High Energy Astrophysics Science Archive
Research Center (HEASARC) Web server at 
http://heasarc.gsfc.nasa.gov/docs/heasarc/fits.html 
and the anonymous ftp access through
ftp://heasarc.gsfc.nasa.gov/fits_info/ provide FITS material.  HEASARC
has developed a the FITSIO package of software routines for easily
reading and writing FITS files, in FORtRAN with a C interface
available, portable to a wide variety of machines.  There is also the
FTOOLS collection of software tools and the VERIFITS FITS conformance
verifier. HEASARC software is available directly through
http://heasarc.gsfc.nasa.gov/docs/heasarc/tech_res_software.html or
ftp://heasarc.gsfc.nasa.gov/fits_info/software/ .

The HEASARC server also provides information from the OGIP/HEASARC FITS
Working Group, (HFWG) the internal legislative body on FITS-related
matters within the Office of Guest Investigator Programs (OGIP) at
NASA/GSFC, at
http://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/ofwg_intro.html or
ftp://heasarc.gsfc.nasa.gov/fits_info/ . The HFWG has developed a number
of FITS conventions that are more specific than the requirements of the
FITS standards. Proposed conventions are publicized to the FITS
community as a whole, with the goal of collaborative development of a
set of conventions that will be accepted throughout the community as
well as within OGIP/HEASARC. 

-------

Direct questions about this posting to 
				Barry M. Schlesinger
				Coordinator,
				FITS Support Office

Electronic mail: fits at nssdca.gsfc.nasa.gov
Telephone:       +1-301-441-4205		

The FITS Support Office is operated under the guidance of the
NASA/GSFC Astrophysics Data Facility.