Subject: sexagesimal TDISPn

From: Sally Hales <segh at mrao.cam.ac.uk>
Date: Thu, 9 Jul 1998 19:52:09 +0100 (BST)

Display of celestial coordinates held internally in degrees in a BINTABLE

Normally, in a FITS browser for example, source coordinates are displayed
to the user in sexagesimal format, converted from the angle held internally
in degrees, since RA,Dec in decimal degrees are not useful for source
recognition etc. However, as things stand at present, there is no way for
the originator of a BINTABLE to specify what sexagesimal precision he deems
appropriate for the display of a celestial coordinate. so the user is left
to make his own arbitrary choice, possibly truncating or spuriously 
extending the meaningful precision of the original data. The obvious place
to make provision for specifying the appropriate sexagesimal precision
would be the TDISPn field - and the fact that so many BINTABLES 
contain celestial coordinates which are not recognisable to the user when
displayed in any of the existing TDISPn formats emphasises the need for
such provision. 

      There are so many respects in which the BINTABLE is superior to
compressed ASCII (which now seems to be favoured by some users, perhaps
because the lack of a standard for the problem above is a stumbling block 
for making a really versatile FITS browser which would be adopted throughout
the astronomical community) - it seems a pity if it is not fully exploited
for want of a solution to this small omission.

      Sally Hales
      MRAO Cambridge UK