From fitsbits-request Tue Apr 6 18:03:25 1993 X-VM-VHeader: ("From:" "Sender:" "Resent-From" "To:" "Apparently-To:" "Cc:" "Subject:" "Date:" "Resent-Date:") nil X-VM-Bookmark: 6 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["548" "" "6" "April" "1993" "21:31:06" "GMT" "Martin Shepherd" "mcs at goblin.caltech.edu " nil "17" "TZERO applied to complex data types in binary tables." "^From:" nil nil "4"]) Received: by fits.cv.nrao.edu (4.1/DDN-DLB/1.5) id AA13313; Tue, 6 Apr 93 18:03:25 EDT Return-Path: Message-Id: <1pssqqINNnv4 at gap.caltech.edu> Organization: California Institute of Technology, Pasadena Path: cv3.cv.nrao.edu!uvaarpa!darwin.sura.net!gatech!howland.reston.ans.net!zaphod.mps.ohio-state.edu!sdd.hp.com!elroy.jpl.nasa.gov!nntp-server.caltech.edu!goblin!mcs From: mcs at goblin.caltech.edu (Martin Shepherd) Sender: fitsbits-request at fits.CV.NRAO.EDU To: fitsbits at fits.CV.NRAO.EDU Subject: TZERO applied to complex data types in binary tables. Date: 6 Apr 1993 21:31:06 GMT In the NOST FITS standard document (Nov 6, 1991) a list of types for which TSCAL and TZERO are undefined is presented (Page 42). Complex types are not in this list. How should TZERO be applied to complex values? Should TZERO be treated as a real number: A+iB -> (TZERO + A x TSCAL) + i(B x TSCAL) or should it be applied to both complex parts as: A+iB -> (TZERO + A x TSCAL) + i(TZERO + B x TSCAL) ? I am going to assume the former for now but would appreciate some clarification. Martin Shepherd (mcs at phobos.caltech.edu) From fitsbits-request Tue Apr 6 18:32:26 1993 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["1300" "Tue" "6" "April" "1993" "23:32:11" "GMT" "Don Wells" "dwells at fits.CV.NRAO.EDU " nil "26" "Re: TZERO applied to complex data types in binary tables." "^From:" nil nil "4"]) Received: by fits.cv.nrao.edu (4.1/DDN-DLB/1.5) id AA13409; Tue, 6 Apr 93 18:32:26 EDT Return-Path: Message-Id: Organization: nrao Path: cv3.cv.nrao.edu!cv3.cv.nrao.edu!dwells References: <1pssqqINNnv4 at gap.caltech.edu> From: dwells at fits.CV.NRAO.EDU (Don Wells) Sender: fitsbits-request at fits.CV.NRAO.EDU To: fitsbits at fits.CV.NRAO.EDU Subject: Re: TZERO applied to complex data types in binary tables. Date: Tue, 6 Apr 1993 23:32:11 GMT In article <1pssqqINNnv4 at gap.caltech.edu> mcs at goblin.caltech.edu (Martin Shepherd) asks: "... How should TZERO be applied to complex values? .." [in tables] The Basic FITS Agreement specifies that value fields will utilize the conventions of Fortran-77 list-directed READs. In this case the relevant text is lines 18-24 on page 13-14 of ANSI X3.9-1978 "Programming Language FORTRAN": "When the corresponding list item is of type complex, the input form consists of a left parenthesis followed by an ordered pair of numeric input fields separated by a comma, and followed by a right parenthesis. The first numeric input field is the real part of the complex constant and second is the imaginary part. Each of the numeric input fields may be preceded or followed by blanks.." While this is surely the proper pedantic answer to the question, it does make me rather nervous because it is improbable that there is any FITS reader that would properly construe such syntax. I advise caution in this matter. -- Donald C. Wells Associate Scientist dwells at nrao.edu National Radio Astronomy Observatory +1-804-296-0277 520 Edgemont Road Fax= +1-804-296-0278 Charlottesville, Virginia 22903-2475 USA 78:31.1W, 38:02.2N From fitsbits-request Tue Apr 6 19:21:22 1993 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["1080" "Tue" "6" "April" "93" "19:21:31" "EDT" "William Pence" "pence at tetra.gsfc.nasa.gov " nil "28" "Re: TZERO applied to complex data types in binary tables." "^From:" nil nil "4"]) Received: by fits.cv.nrao.edu (4.1/DDN-DLB/1.5) id AA13733; Tue, 6 Apr 93 19:21:22 EDT Return-Path: Message-Id: <9304062321.AA22539 at tetra.gsfc.nasa.gov> From: pence at tetra.gsfc.nasa.gov (William Pence) Sender: fitsbits-request at fits.CV.NRAO.EDU To: fitsbits at fits.CV.NRAO.EDU Cc: pence at tetra.gsfc.nasa.gov Subject: Re: TZERO applied to complex data types in binary tables. Date: Tue, 6 Apr 93 19:21:31 EDT Martin Shepherd wrote on 6 April: >Should TZERO be treated as a real number: > > A+iB -> (TZERO + A x TSCAL) + i(B x TSCAL) > >or should it be applied to both complex parts as: > > A+iB -> (TZERO + A x TSCAL) + i(TZERO + B x TSCAL) ? > >I am going to assume the former for now but would appreciate some >clarification. The first formula is correct in a strict algebraic sense, but I think the second formula is more appropriate in FITS applications. Some computer languages don't support a complex data type, and most do not support the double complex (M) FITS data type, so many FITS readers will probably internally interpret a '1C' binary table column as a '2E' column, and a '1M' column as a '2D' column. Then one would more naturally want to apply the second formula to scale the input FITS values. As a practical matter however, it doesn't make much sense to scale a floating point binary table column, does it? Why not just write the scaled values directly in the table, and thus save the scaling overhead each time the FITS file is read? -Bill Pence From dwells Wed Apr 7 09:32:23 1993 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["3278" "Wed" "7" "April" "93" "09:32:22" "EDT" "Don Wells" "dwells " nil "83" "Creation of a Usenet Newsgroup for Scientific Data Formats/Models" "^From:" nil nil "4"]) Received: by fits.cv.nrao.edu (4.1/DDN-DLB/1.5) id AA15822; Wed, 7 Apr 93 09:32:23 EDT Return-Path: Message-Id: <9304071332.AA15816 at fits.cv.nrao.edu> From: dwells (Don Wells) Sender: fitsbits-request at fits.CV.NRAO.EDU To: fitsbits Subject: Creation of a Usenet Newsgroup for Scientific Data Formats/Models Date: Wed, 7 Apr 93 09:32:22 EDT I am forwarding the appended announcement to sci.astro.fits/fitsbits because of the obvious relevance. The RFD mentions FITS because I communicated with the proposers some days ago. I expect that I will vote YES on this newsgroup because I think that the subject of scientific data models is fundamental and needs to be discussed in a multi-disciplinary context. -Don ------- Start of forwarded message ------- There is currently ongoing discussion in news.groups for the creation of a Usenet Newsgroup for discussing the storage and retrieval of scientific data. There appears to be a consensus for putting this newsgroup in the sci hierarchy. However, we still need to select a name. The following names have been proposed: sci.data sci.datamodels sci.dataaccess sci.dataformats I am going to conduct an informal poll this week. Please VOTE for which of the above names you would recommend we adopt. Informal voting will take place until Thursday, April 8, 1993 at 11:59pm. Based on the results of this informal poll, the Call For Votes will most likely be issued on or about April 9th, 1993. Send ALL votes to briand at ncsa.uiuc.edu The current RFD is Shown below. If you would like to make additions or deletions to this charter, please also send those changes to the above address. Discussion is ongoing in news.groups. - -- Briand Sanderson NCSA HDF Programmer ====================================================================== REQUEST FOR DISCUSSION: of Creation of an UNMODERATED Usenet newsgroup called "sci." for discussing the storage and retrieval of scientific data. PURPOSE: The purpose of the newsgroup "sci." would be for discussing information related to the use of the scientific data formats such as HDF, netCDF, FITS, and various others. Topics of discussion could include problems encountered using specific formats, questions about where to get the code for data format programs, discussions of specific uses of data format programs, etc. It is anticipated that readers of the group would be scientists (and software developers) who use data formats/models such as HDF, netCDF, and other such programs. RATIONALE: There are many data formats designed specifically for scientific applications. Many have been adopted as a standard by scientific organizations ranging over such diverse fields as astronomy, physics, chemistry, medical research, health care, space science, atmospheric sciences, earth sciences and environmental science. It is hoped that the creation of the group, "sci." will encourage and facilitate a greater amount of collaboration and sharing of information and experience between individuals and groups. NEWSGROUP CREATION: The discussion period is continuing. It is anticipated that a call for votes will occur around April 9, 1993. Please post all discussions to "news.groups" ------- End of forwarded message ------- Donald C. Wells Associate Scientist dwells at nrao.edu National Radio Astronomy Observatory +1-804-296-0277 520 Edgemont Road Fax= +1-804-296-0278 Charlottesville, Virginia 22903-2475 USA 78:31.1W, 38:02.2N From fitsbits-request Wed Apr 7 23:26:07 1993 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["1298" "Wed" "7" "April" "1993" "21:57:09" "GMT" "William Thompson" "thompson at serts.gsfc.nasa.gov " nil "37" "Re: TZERO applied to complex data types in binary tables." "^From:" nil nil "4"]) Received: by fits.cv.nrao.edu (4.1/DDN-DLB/1.5) id AA17595; Wed, 7 Apr 93 23:26:07 EDT Return-Path: Message-Id: Organization: NASA Goddard Space Flight Center - Greenbelt, MD USA Path: cv3.cv.nrao.edu!uvaarpa!darwin.sura.net!wupost!howland.reston.ans.net!agate!ames!nsisrv!news1.gsfc.nasa.gov!serts.gsfc.nasa.gov!thompson References: <1pssqqINNnv4 at gap.caltech.edu> From: thompson at serts.gsfc.nasa.gov (William Thompson) Sender: fitsbits-request at fits.CV.NRAO.EDU To: fitsbits at fits.CV.NRAO.EDU Subject: Re: TZERO applied to complex data types in binary tables. Date: Wed, 7 Apr 1993 21:57:09 GMT mcs at goblin.caltech.edu (Martin Shepherd) writes: >In the NOST FITS standard document (Nov 6, 1991) a list of types for >which TSCAL and TZERO are undefined is presented (Page 42). Complex >types are not in this list. How should TZERO be applied to complex >values? >Should TZERO be treated as a real number: > A+iB -> (TZERO + A x TSCAL) + i(B x TSCAL) >or should it be applied to both complex parts as: > A+iB -> (TZERO + A x TSCAL) + i(TZERO + B x TSCAL) ? >I am going to assume the former for now but would appreciate some >clarification. >Martin Shepherd (mcs at phobos.caltech.edu) I would also assume the former, based on looking at it as an equation, i.e. Ctrue = Tzero + Cfits * Tscal Cfits = A + i * B ===> Ctrue = Tzero + (A + i*B)*Tscal = (Tzero + A*Tscal) + i*B*Tscal I work in IDL. Our software works by choosing what kind of datatype to assign to a FITS header record from the way it is written, rather than by making an a priori assumptions. Thus, we would be able to handle a case where either or both of TZERO and TSCAL were themselves complex numbers, so long as the recommended fixed formats were followed (section 5.3 of the NOST standard). However, a strict reading of the FITS standard does not appear to allow this. Bill Thompson From fitsbits-request Fri Apr 16 15:19:47 1993 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] [nil nil nil nil nil nil nil nil nil nil nil nil "^From:" nil nil nil]) Received: by fits.cv.nrao.edu (4.1/DDN-DLB/1.5) id AA01631; Fri, 16 Apr 93 15:19:47 EDT Return-Path: Message-Id: Organization: NASA Goddard Space Flight Center - Greenbelt, MD USA Path: cv3.cv.nrao.edu!uvaarpa!caen!uwm.edu!spool.mu.edu!howland.reston.ans.net!gatech!ukma!news1.gsfc.nasa.gov!nssdca.gsfc.nasa.gov!bschlesinger From: bschlesinger at nssdca.gsfc.nasa.gov (BARRY M. SCHLESINGER) Sender: fitsbits-request at fits.CV.NRAO.EDU To: fitsbits at fits.CV.NRAO.EDU Subject: FITS basics and information (periodic posting) Date: Fri, 16 Apr 1993 16:33:00 GMT Followups to: poster Keywords: Message-ID: <16APR199312332735 at nssdca.gsfc.nasa.gov> Organization: NASA - Goddard Space Flight Center News-Software: VAX/VMS VNEWS 1.41 This basic FITS information is posted and updated periodically for the benefit of new readers and the reference of old readers. FITS (Flexible Image Transport System) is a data format designed to provide a means for convenient exchange of astronomical data between installations whose standard internal formats and hardware differ. A FITS file is composed of a sequence of Header Data Units (HDUs). The header consists of keyword=value statements, which describe the format and organization of the data in the HDU and may also provide additional information, for example, about the instrument or the history of the data. The data follow, structured as the header specifies. The data section of the HDU may contain a digital image, but, except for the first, *it doesn't have to*. Other possible formats include tables and multidimensional matrices that are not images. The first HDU must contain a multidimensional matrix or no data at all; the data in subsequent HDUs, called extensions, may be of any type, consistent with certain rules. The "Image" in the name comes from the original use of the format to transport digital images, but it's not just for images any more. FITS is not principally a graphics format designed for the transfer of pictures; it does not incorporate "FITS viewers", packages for decoding the data into an image. Users must develop or obtain separate software to convert the data from the FITS file into a form that can be readily displayed. As has been discussed in this newsgroup, and in alt.sci.astro.fits before it, the Extended Portable Bitmap Toolkit (pbm+) can be used for converting many FITS files to such a format. However, support is not guaranteed for all FITS files where the data are in the form of an image. In particular, there may be problems when the data matrix members are in IEEE floating point format (BITPIX<0) or the matrix has more than two dimensions (NAXIS>2). Archie Warnock and Ron Baalke have announced release of version 7.8 of the IMDISP program. IMDISP is an interactive image processing program that runs on an IBM PC computer and supports FITS input. IMDISP 7.8 is available via anonymous ftp at ames.arc.nasa.gov [128.102.18.3] in a file called imdisp78.zip in the pub/SPACE/SOFTWARE subdirectory and at hypatia.gsfc.nasa.gov in the pub/software/imdisp subdirectory. It is also available through Simtel-20 [192.88.110.20] at PD1:IMDISP78.ZIP. Additional discussion of FITS->image converters appears in this newsgroup from time to time. The fundamental references on FITS are the following four papers, often referred to collectively as the "Four FITS Papers". These papers are the formal standard for FITS, endorsed by the International Astronomical Union (IAU). Wells, D. C., Greisen, E. W., and Harten, R. H., "FITS: a flexible image transport system," Astronomy and Astrophysics Supplement Series, 44, 363-370, 1981. Greisen, E. W. and Harten, R. H., "An extension of FITS for small arrays of data," Astronomy and Astrophysics Supplement Series, 44, 371-374, 1981. (NOTE: The format described in this paper has been used almost exclusively to transport radio interferometry and is likely to be replaced by other formats in the future. Writing data other than radio interferometry data using this format is not recommended.) Grosbol, P., Harten, R. H., Greisen, E. W., and Wells, D. C., "Generalized extensions and blocking factors for FITS," Astronomy and Astrophysics Supplement Series, 73, 359-364, 1988. Harten, R. H., Grosbol. P., Greisen, E. W., and Wells, D. C., "The FITS tables extension, Astronomy and Astrophysics Supplement Series, 73, 365-372, 1988. A User's Guide for FITS, commissioned by NASA Headquarters, is maintained by the NASA/OSSA Office of Standards and Technology (NOST) FITS Support Office. This Guide is intended to be a tutorial for new FITS users. In addition to presenting the rules of FITS, it provides some of the history and reasoning behind the choice of the rules, adds recommendations on good practices, and discusses current developments in FITS. The current version, 3.0, was issued in January 1993. This document is at present available only in printed form, but steps are under way to generate a PostScript version that will work on many systems and a flat ASCII version. The NOST is sponsoring development of a formal standard for FITS. The goal is a document codifying FITS as endorsed by the IAU, eliminating some contradictions and ambiguities in the original FITS papers, that can be endorsed by the IAU FITS Working Group as the FITS standard. The document is being developed by a Technical Panel chaired by Dr. Robert J. Hanisch (STSci), with review by the astronomical community. Only minor revisions are expected to the draft currently available, version 0.3b, but the form of the standard is not final, and it does not supersede the four papers and Floating Point Agreement endorsed by the IAU as the official standard for FITS. The IAU has endorsed the Floating Point Agreement, which defines how floating point numbers are to be expressed in FITS. The basic agreement appears verbatim in the User's Guide, and the substance is incorporated in the Draft NASA FITS definition. The NOST maintains a file of FITS information available by anonymous ftp from nssdca.gsfc.nasa.gov or DECnet copy from NSSDCA, in the directory FITS. It includes copies of the current NASA draft standard in flat ASCII, PostScript, and LaTeX. Style and index files are provided for the LaTeX form. Except that the ASCII form does not have an index, the copies in the three formats are identical; only one need be retrieved. A current list of the extension type (structure) names registered with the IAU FITS Working Group is maintained. Also available, in LaTeX form, is the text of the proposal for one of these new extension types, IMAGE. A modified version of this posting also appears there. An AAREADME.DOC file describes the contents of the directory. A SOFTWARE subdirectory contains a program in C to read and list the headers of a FITS file and another file with information on publicly available FITS software packages. The ERRTEST subdirectory contains several versions of the same FITS file, a valid one and several with different kinds of header errors, for use in testing software to read FITS files. Be sure to use binary transfer for ftp access of FITS test files. Both the SOFTWARE and ERRTEST subdirectories include AAREADME.DOC files describing their content. The README files with names other than AAREADME.DOC are now pointers to the AAREADME.DOC files; the names have been retained for the convenience of users who may have learned about the directory from material that uses the old name. A modified version of this posting is now in the main directory. Additional material can be obtained by anonymous ftp from the National Radio Astronomy Observatory, from fits.cv.nrao.edu, in the directory FITS. The Documents subdirectory (case is significant) contains copies of the BINTABLE Binary Tables extension proposal, which is now under consideration by the FITS committees, and a draft describing a proposed method for incorporating data compression under FITS. A number of additional documents are available in ASCII text form, including the proposal on physical blocking of FITS files on media other than tape, and material on FITS, its history, and the FITS community. Its FITS_wcs subdirectory contains material serving as the basis for continuing discussion of world coordinates issues, some of which appears on this newsgroup from time to time. One is a draft proposal for world coordinates conventions being developed by E. Greisen and M. Calabretta. Two AIPS memos describing projections from a sphere onto a plane are also included, in PostScript form. A copy of an earlier paper by D. Wells and R. Hanisch summarizing conclusions of a workshop on World Coordinates held in Charlottesville in 1988 mremains in the Documents subdirectory. Unless otherwise noted, documents are available from NRAO in both LaTeX and PostScript forms. There is an AA.README file for the Documents subdirectory and a README file for its FITS_wcs subdirectory. Printed copies of many of the documents listed above can be obtained from the NOST Librarian. Printed copies of the User's Guide and either paper or electronic copies of the Draft NOST Standard, for those without ftp access, are available. Because of restrictions set by the copyright holder, NOST can send copies of the four FITS papers only to non-profit organizations. The NOST can be reached as follows: (Postal) NASA/OSSA Office of Standards and Technology Code 633.2 Goddard Space Flight Center Greenbelt MD 20771 USA (Internet) nost at nssdca.gsfc.nasa.gov (DECnet) NCF::NOST Telephone: (301)286-3575 8 a. m. - 5 p. m., U. S. Eastern Time If the Librarian is unavailable, a phone mail system takes the call after four rings. Please mention this posting in your request. Use the FITS office electronic mail address below for replies or questions. It is monitored by other NOST staff memebers when I am away from the office and provides a greater certainty of rapid response. Barry M. Schlesinger Coordinator, NASA/NSSDC NOST FITS Support Office (301) 513-1634 fits at nssdca.gsfc.nasa.gov NCF::FITS