|
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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 | |
|
|
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 09:24 PM |
[fitsbits] Dataset identifications. | Thomas McGlynn | FITS | 0 | March 10th 04 07:20 PM |
[fitsbits] On-line FITS-WCS visualisation | David Berry | FITS | 0 | March 4th 04 03:36 PM |
[fitsbits] (fwd) Windows Explorer Fits Viewer | Eddie Trimarchi | FITS | 0 | February 24th 04 06:46 PM |