A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » FITS
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

[fitsbits] TDIMn



 
 
Thread Tools Display Modes
  #11  
Old August 30th 04, 08:55 PM
Daniel Durand
external usenet poster
 
Posts: n/a
Default

Thierry

You will find the relevant information regarding the usage of CFITSIO
for the CFHTLS archive
at CADC on the following web page:

http://cadcwww.hia.nrc.ca/cfht/cfitsio_comp.html

Daniel


On 30-Aug-04, at 12:24 PM, Thierry Forveille wrote:

William Pence writes:
**** - Mosaic CCD camera data taken at the Canada-France-Hawaii
****** Telescope (CFHT) and publicly distributed by the CADC.
*
??? As far as I know, mosaic images taken at CFHT are distributed
as multiple IMAGE extensions (one extension per CCD). It is of
course possible that the CADC repackages them in a new format, but
that would be new to me. Do you have a pointer to where you got this
information from?

_______________________________________________
fitsbits mailing list

http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits

Daniel Durand | Tel/Tél: +1 250 363 0052 | FAX: +1 250 363 0045
HST archives scientist | Responsable Archive HST
Herzbergh Institute of Astrophysics | Institut Herzberg
Astrophysique
National Research Council Canada | Conseil National de Recherches du
Canada
5071 W. Saanich Road | 5071 W. Saanich Road
Victoria, B.C. | Victoria, C.B.
Canada V9E 2E7

  #12  
Old August 31st 04, 09:20 AM
Clive Page
external usenet poster
 
Posts: n/a
Default

I would like to support the message from Jonathan McD: X-ray astronomy
tables do indeed make extensive use of the TDIMn and variable length array
facilities.

On Mon, 30 Aug 2004, William Pence wrote:

B.3 The "Substing Array" convention


I'm not aware of any software packages or any FITS data files that support
or use the full form of this proposed convention, as in these examples:


TFORMn = '30A:SSTR10' / fixed length 10-char substrings


I have used this convention myself for FITS files I have generated and
used internally, but I am not sure that it has been used much in files
distributed externally. If one wants a vector column of a numerical data
type one simply uses e.g. 5E rather than 1E, which is simple to do and
understand. The same facility for strings needs the fixed-length
substring notation, otherwise you just get an array of chars.

I suspect that vector columns are not widely used for two reasons: (1)
ignorance, (2) the false assumption that not many utilities can handle
them. This leads to results which are not always very elegant, for
example the 1XMM catalogue of serendipitous sources from XMM-Newton has
been circulated as a table with 394 columns. If vector columns had been
used for sets of related items (e.g. for the 3 telescopes on board), there
would have been many fewer columns, and the naming could have been simpler
and less obscure.

As it is, however, if one wishes to ingest a FITS table into a relational
DBMS, then the vector-free form is easier to use, since few DBMS support
vector columns.

It is hard to know the right balance he on the whole I think that
vector columns in FITS files are useful and here to stay, so they should
be incorporated into the Standard. It is something of an anomaly that
FITS has no notation of a character "string" only of an array of char
(perhaps following the primitive notation of the C language rather than
the more sensible ones of say Fortran or Python). On grounds of
consistency with the other data types, therefore, it seems to me a good
idea also to incorporate the substring notation into the Standard.


--
Clive Page
Dept of Physics & Astronomy,
University of Leicester,
Leicester, LE1 7RH, U.K.

  #13  
Old August 31st 04, 03:59 PM
William Pence
external usenet poster
 
Posts: n/a
Default

Clive Page wrote:

On Mon, 30 Aug 2004, William Pence wrote:

B.3 The "Substing Array" convention

I'm not aware of any software packages or any FITS data files that support
or use the full form of this proposed convention, as in these examples:

TFORMn = '30A:SSTR10' / fixed length 10-char substrings


I have used this convention myself for FITS files I have generated and
used internally, but I am not sure that it has been used much in files
distributed externally. If one wants a vector column of a numerical data
type one simply uses e.g. 5E rather than 1E, which is simple to do and
understand. The same facility for strings needs the fixed-length
substring notation, otherwise you just get an array of chars.


If it is only necessary to support arrays of fixed length substrings in a
FITS binary table column, then the TDIMn convention could be used, and there
would be no need for the substring conventions. So instead of

TFORM2 = '30A:SSTR10'
or
TFORM2 = '30A10'

one would have:

TFORM2 = '30A'
TDIM2 = '(10,3)

where it is understood that the size of the most rapidly varying dimension
(10 in this case) should be interpreted as the length of each substring.
This usage is discussed in the B.2 and B.3 appendices to the Nost FITS Standard.

The more complex 'SSTR' convention would only have to be used to support
arrays of variable length substrings, as in

TFORMn = '30A:SSTR10/037'

which in this case means that the table column is 30 characters wide and
contains variable length substrings that are each terminated with a '%'
percent character (ASCII 037) with a maximum length of 10 characters.
Examples of the table fields in this case might look like this:

'Robert%Joe%James%Alexander%Sue'
'Sally%Thomas%Natalie%Guillaume'

where the first row contains 5 substrings and the 2nd row has 4 substrings.
I wonder if there is really much need for this feature for astronomical
data files? If VOTables support this sort of data structure (?) then we
might also need this capability within FITS for data interoperability.

Bill
--
__________________________________________________ __________________
Dr. William Pence
NASA/GSFC Code 662 HEASARC +1-301-286-4599 (voice)
Greenbelt MD 20771 +1-301-286-1684 (fax)


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
[fitsbits] New draft of WCS Paper IV Mark Calabretta FITS 0 April 27th 04 05:20 AM
[fitsbits] WCS Paper III Eric Greisen FITS 2 March 17th 04 10:24 PM
[fitsbits] Dataset identifications. Thomas McGlynn FITS 0 March 10th 04 08:20 PM
[fitsbits] On-line FITS-WCS visualisation David Berry FITS 0 March 4th 04 04:36 PM
[fitsbits] (fwd) Windows Explorer Fits Viewer Eddie Trimarchi FITS 0 February 24th 04 07:46 PM


All times are GMT +1. The time now is 05:42 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.