[fitsbits] Re: Endian state of multibyte Binary Data in FITS files

[Chris Lawton]

Milton Aupperle <milton at SAPMMUSTDIEoutcastsoft.com.invalid> writes:

> First time poster and  a FITS newbie.
> 
> I'm working on exporting FITS files from the API of a Astronomical CCD
> Camera for Mac OS X (PowerPC processors Big Endian).  The binary images
> are 16 bit Unsigned  grayscale with the proper flags to indicate it is
> unsigned and how to convert it to. I have it all implemented and all
> the Mac FITS viewers I've used are happy with the FITS file it creates.
> 
> However, I'm somewhat concerned about Endian ness of the Binary data.
> I've looked through the various FITS specifications that I could find
> on the Web or in PDF, but I have as yet not found a FITs tag that
> indicates what endian the data is in.
> 
> Can anyone suggest a URL where I can find out about how to indicate or
> determine what Endian multibyte data is in?
> 
> Thanks in Advance..
> 
> Milton Aupperle
> www.outcastsoft.com
> miltons (at) outcastsoft (dot) com


All data is big endian.  Take a look at page 29 of the PDF version of the FITS
NOST Standard.  It says, "The byte that indicates the sign bit shall be first,
and the byte that has the ones bit shall be last."

-Chris