[fitsbits] HEALPIX fits files

[Mark Calabretta]

On Thu 2005/01/13 13:47:05 CDT, Wayne Landsman wrote
in a message to: fitsbits at donar.cv.nrao.edu

>with a map projection, which will incorporated in V3.7  (not yet 
>released?) of WCSLIB.

Should be released sometime soon.

>I think this should eventually allow 
>astronomical display programs (DS9, AIPS) to convert Healpix maps to any 
>desired projection.

HEALPix data is best displayed in the HEALPix projection itself because
no regridding is required, you see the data directly without potential
artifacts introduced by regridding.  All that is required is for a
utility program to reorganize the 1-D vector (ring or nested) onto the
2-D grid.  The HPX projection type can then be used to add a graticule
and this can be saved as a 2-D FITS image and viewed with any software
that understands FITS WCS (with HPX).

However, such an image is presented with an odd 45 deg rotation (handled
in the WCS via a PCi_j or CDi_j matrix).  The double-pixelisation
eliminates this but is not as yet supported by any software.

Mark Calabretta
ATNF