[fitsbits] top or buttom

[Steve Allen]

On Thu 2000-04-20T13:44:18 -0700, Stephen Walton hath writ:

> One point about this which I've always found somewhat confusing (though
> maybe I'm the only one):  We usually consider the indices of an array
> stored in memory as being (row,column) by analogy to mathematical
> matrices.  But, if we adopt the convention that the first axis of a FITS
> image is displayed horizontally and the second vertically, the first index
> of the array is, in effect, the column index;  i.e., the Y coordinate.

The first axis?

Actually, around here we all think of the FITS coordinates of a 2-d
image like this:
	array [ NAXIS2 ][ NAXIS1 ]
So the first is last and that last is first, which is thinking in C
with a concommitant notion that the display will follow video
conventions (i.e., scan lines to the right starting at upper left).

I think the guidelines have to be
1) choose a default convention for display
2) understand the history and reasoning behind why that choice was made
3) document both 1) and 2)
4) provide an interface that permits alternative choices
5) make sure that the WCS proposal is one of those choices

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
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