[fitswcs] Re: distorted TAN projections for SIRTF

[David Berry]

> >Do you feel that we should avoid the IRAF TNX projection?  If so,
> >will the PVi_xs representation of a distorted gnomic projection be 
> >implemented in WCSLIB soon?

If it's any help, the AST library developed and distrubuted by the UK
Starlink project has implemented all the proposals of WCS papers 1 and 2
(excluding the pixel regularization image). This includes the PVi_j terms
for the distorted TAN projecton, and multiple WCS representations. AST can
also read the common forms of TNX and ZPX projections (but only writes TAN
and ZPN). It will also read (and write) various old WCS encodings such as
those which use CROTA or PC keywords to represent rotation, etc.
 
AST includes other WCS facilities as well as simply reading and writing
FITS headers, and transforming between sky and pixel coordinates. For
example, it can convert between most common celestial coordinate systems
and also draw coordinate grids for any arbitrary (potentially
discontinuous) mapping, including all-sky projections etc. The new DS9
image browser from SAO uses AST for these reasons. AST is written in C but
has both C and Fortran interfaces.

If anyone wants further information about AST, the current version of the
documentation for the C interface is available at

http://www.ast.man.ac.uk/~dsb/sun211.htx/sun211.html

A slightly older version of the documention for the Fortran interface 
is available at:

http://www.starlink.rl.ac.uk/star/docs/sun210.htx/sun210.html


David Berry