On Thu, 17 Aug 2006, Peter W. Draper wrote:
> On Fri, 11 Aug 2006, Mark Taylor wrote:
>
> > Peter when you're back, or anybody else who knows,
> >
> > I've got a funny with GAIA. There is an image file and a catalogue file
> > at
> >
> > ftp://andromeda.star.bris.ac.uk/pub/star/data/gaia/iras_psc.fits
> > messier.TAB
> >
> > These are basically full-sky data sets. If I load the FITS file and
> > then the catalogue (Data-Servers|Local Catalogs|Load from file...),
> > not all the points from the catalogue show up, only those within
> > a certain RA range (e.g. M1 and M2 are missing, the first one visible
> > is M3). If I subsequently Select Area... over a missing part of the
> > data (e.g. top left) followed by Search, the missing objects in
> > the selected region show up.
> >
> > I suspect this could be a bug related to the fact that the field of
> > view is very large (whole sky). However it may be some kind of a
> > feature that I don't understand.
>
> Hi Mark,
>
> as you suspected this is down to the size (on the sky) of the image. I
> just run astDistance to get some "radius" of the image in radians, but
> clearly at this scale there's a shorter way around the great circle
> between the two points I've chosen (bottom left and centre of image).
>
> David, is there a better way to size an image in world coordinates?
Probably best to use an additional point mid way between the corner and
the centre of the image, then use astDistance twice (i.e. get the distance
from corner to mid-point, and then get the distance from mid-point to
centre) and just add the two distances together.
David
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