|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
FITS long integer support (was [fitsbits] ADASS FITS BoFon Sunday)
We should perhaps consider adding a short section to the FITS Standard to
clarify the status of long (64-bit) integer support in FITS for the benefit of users. Here is a first cut at the main points we might want to make. Any comments? 1. There is in principle no limit on the magnitude of integer keyword values in FITS headers and on the values in integer columns in ASCII tables, however many existing software packages only support values within the range of a signed 32-bit integer (-2147483648 to +2147483648). This effectively limits the sizes of FITS images and tables (as given by the NAXISn keywords). 2. FITS does not officially support 64-bit twos-complement signed binary integers in either primary array images, image extensions, or columns in binary tables. 3. Informal proposals have been made to support 64-bit FITS images with BITPIX = 64 and 64-bit integer columns in binary tables with TFORMn = 'rK' (where 'r' here represents an integer repeat value). It has also been proposed to support a 64-bit variable length array descriptor format in binary tables using a TFORMn keyword with data type = 'Q' (analogous to the existing 32-bit 'P' variable length array descriptor format). 4. Some FITS software packages support these informal proposals on a trial basis, however FITS file designers are urged to use these formats with caution. These formats should only be used in cases where a) there is no reasonable alternative way to represent the information using standard FITS formats, and b) where it is reasonably certain that the software packages that are required to read the FITS files have been specifically designed to support the long integer FITS formats. 5. It is possible that the FITS Standard might be modified in the future to officially support images with BITPIX = 64 and/or binary table columns with TFORMn = 'K' or 'Q'. Developers of new FITS software may wish to anticipate this possibility and add compatibility with these possible future formats. -- __________________________________________________ __________________ 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] Start of the FITS MIME type Public Comment Period | William Pence | FITS | 8 | June 17th 04 06:08 AM |
Reading floating point FITS files | John Green | FITS | 34 | November 29th 03 01:31 AM |