[fitsbits] generic coordinate system

[Mark Calabretta]

On Sun 2002/07/14 16:35:43 GMT, "Salvatore Lorusso" wrote
in a message to: fitsbits at donar.cv.nrao.edu

>if for example I save the density rho(i,j) in a plane, the trasformation
>between
>numerical coordinates i,j and physical coordinate system x(i,j) y(i,j) is
>not

Salvatore,

FITS currently handles 2-D coordinate transformations of the type
(x,y) = f(i,j) where f() is either a linear function, or a spherical
projection.  It would only be a matter of luck if one of these matched
your particular application.

Additional 1-D non-linear functions are in the pipeline, but these will
also be based on predefined functional forms chosen for specific purposes
(spectral coordinates in this case).

General n-D distortion functions are also coming, but again based on
predefined functional forms.

>trivial. I'm thinking to save also x(i,j) and y(i,j) as 'images' in the FITS
>file, but

This is also coming - it may be your best bet for now, but I don't know
of any existing software that can interpret it.

>it would be useful to have a software to display rho vs (x,y).

PGSBOX, based on PGPLOT, can draw general curvilinear coordinate grids
on an image - you have to supply functions which compute f() and its
inverse.

>Do you know if there is some software that can do it?

PGSBOX comes with WCSLIB - http://www.atnf.csiro.au/~mcalabre.  Refer to
the three publically available WCS papers there.  A fourth paper is in
preparation.

Mark Calabretta
ATNF