[fitsbits] polar coordinates

[David Berry]

On 12 December 2013 13:48, Phil Hodge <hodge at stsci.edu> wrote:
> Walter,
>
> Aside from the log, isn't this the ARC projection with CRVAL1 and CRVAL2
> set to the right ascension and declination at the center of the
> (theoretical) disk?

I'm not sure how that would work. Can you give an example? Typing the following:

NAXIS1  = 1000
NAXIS2  = 1000
CTYPE1  = 'RA---ARC'
CTYPE2  = 'DEC--ARC'
CRPIX1  = 500
CRPIX2  = 500
CDELT1  = -0.001
CDELT2  = 0.001
CRVAL1  = 45.0
CRVAL2  = 45.0

into the "Headers" box at
http://starlink.jach.hawaii.edu/cgi-bin/ast/fits-plotter, putting
"grid=1" into the "Plot settings" box, and pressing the "Submit"
button just produces a roughly recti-linear grid as you might expect.

I'm not sure how using an ARC projection gets round the issue that
FITS-WCS can only describe latitude, not co-latitude.

David