[fitsbits] How is NAXISn supposed to work?

[Peter Teuben]

ok, gently then. The crux is the (english) language I guess:

"index along axis 1 varies most rapid'
		    ^^^^^^      ^^^^^

wihch refers to how an array DATA(i,j,k,....)  is indexed.
What they mean to say is that in a 2D example element DATA(i,j)
is followed by DATA(i+1,j)   [and not DATA(i,j+1)].

This is the fortran style of indexing, as opposed to the C style
of indexing, where the last index varies most rapidly.

If I reread the sentence, I'm not confused about the values of NAXISi,
or that NAXIS1 > NAXIS2.., but then again, I've been looking at, and
using this type of data for some time.

- peter



On [Mon Apr 27 17:54], RPEHLM wrote:
> Hello folks,
> 
> I'm a simple sort of chap, so I have a simple question! <g>
> 
> Reading the IAUFWG v3 (2008 July 10) documentation for the Primary Data 
> Array (page 14, section 3, sub 3.3.2).  I'm not understanding what is 
> meant by:
> 
> "Arrays of more than one dimension shall consist of a sequence such
> that the index along axis 1 varies most rapidly, that along axis 2 next 
> most rapidly, and
> those along subsequent axes progressively less rapidly, with that along 
> axis m, where
> m is the value of NAXIS, varying least rapidly."
> 
> Does axis 1 equate to NAXIS1 and axis 2 to NAXIS2 etc.?  Should the 
> value of NAXIS1 be greater than NAXIS2, which in turn should be greater 
> than NAXIS3 etc.?
> Or should the value of NAXIS1 be the smallest and NAXISn the greatest?  
> Or something else entirely?  For example, take a 100 by 200 array, would 
> the following be correct:
> 
> NAXIS = 2
> NAXIS1 = 100
> NAXIS2 = 200
> 
> or this:
> 
> NAXIS = 2
> NAXIS1 = 200
> NAXIS2 = 100
> 
> (Yes, I know the formatting is not exactly right <g>)
> 
> The documentation would seem to indicate the former, but I have seen 
> plenty of commercial applications implementing the later.  Hence the 
> confusion to my poor abused grey thing.
> 
> Regards
> Robin
> P.S. My first posting so please be gentle!!!
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