[iaufwg] Voting result on the FITS Standard

[William Thompson]

Steve Allen wrote:
> On Mon 2008-05-19T18:49:57 -0400, William Thompson hath writ:
>> Integral pixel coordinate values coincide with the corresponding array indices,
>> while fractional pixel coordinate values lie between array indices and thus
>> imply interpolation.
> 
> I see that we are on the verge of adding content to the standard
> by talking about fractional pixel coordinate values.
> 
> The GeoTIFF spec has a flag indicating whether the array values
> should be interpreted as "point samples" or "bins".
> FITS has never had this.
> 
> Bins have boundaries, samples can be interpolated.
> The former is implicitly best interpolated akin to a histogram,
> the other raises questions of multidimensional splines.
> It's a potentially contentious subject.

Nearest neighbor is an interpolation technique which is appropriate for binned data.

> If we include language which goes any further than the text in
> the WCS paper we may be making a substantive modification.

The WCS paper goes rather further, stating explicitly that integral pixel 
numbers refer to the center of pixels, and goes on to say that the first pixel 
runs from 0.5 to 1.5.  That's a much stronger and more restrictive statement 
about the extent of a pixel.  The suggested language avoids this added content.

It might be good to add a statement to the effect that the standard does not 
specify how the data are to be interpolated to fractional pixels.

Bill Thompson

> --
> Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
> UCO/Lick Observatory        Natural Sciences II, Room 165    Lat  +36.99855
> University of California    Voice: +1 831 459 3046           Lng -122.06015
> Santa Cruz, CA 95064        http://www.ucolick.org/~sla/     Hgt +250 m
> _______________________________________________
> iaufwg mailing list
> iaufwg at listmgr.cv.nrao.edu
> http://listmgr.cv.nrao.edu/mailman/listinfo/iaufwg
> 

-- 
William Thompson
NASA Goddard Space Flight Center
Code 671
Greenbelt, MD  20771
USA

301-286-2040
William.T.Thompson at nasa.gov

(Note changed email address)