[fitsbits] generic coordinate system

[David Berry]

Salvatore,

> I'm evaluating the possibility to use the FITS format to save the results of
> my numerical simulations. The problem is that I may have not regular grids,
> so
> 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
> trivial. I'm thinking to save also x(i,j) and y(i,j) as 'images' in the FITS
> file, but
> it would be useful to have a software to display rho vs (x,y).
> 
> Do you know if there is some software that can do it?

You may be interested in the Starlink AST library:

http://www.starlink.ac.uk/star/docs/sun211.htx/sun211.html

This provides facilities for storing, managing and plotting fairly general
WCS schemes, including various pre-defined forms (such as the proposed
FITS WCS), arbitrary algebraic transformations, look-up table based
transformations, etc. AST can stored descriptions of all these WCS systems
within FITS headers using its own keyword system (it can also read and
write WCS in the form of the Greisen and Calabretta FITS papers
proposals, so long as your WCS can be described in terms of the model
proposed by the papers, which may not be the case for yours).

AST also provides facilities for plotting arbitrary non-linear axes which
are independant of graphics system. Facilities for using PGPLOT as the
underlying graphics system are included with the library, but if you want
to use some other graphics package you just have to write a simple module
which tells AST how to draw a straight line and  plot a character string.
Starlink can provide such modules to allow Tcl/Tk or Java Swing to do the
drawing (a JNI binding for the library is also available, also a fortran 
77 binding).

David