On Mon, 31 May 2010, Edward Chapin wrote:
> >> this is a known problem area for GAIA. What you've got is a mapping that
> >> is using a lookup table for the 54000 coordinates in your third dimension.
> >> To pass these around in the Skycat layers it is necessary to feed these
> >> into and back out of a FITS encoding, that's where all the time is going.
> >>
> >> The best way around this is to use a linear mapping if you can.
> >
> > OK, thanks for the response. The fact that it is slow for one data
> > cube but not another (which in theory have identical dimensions/tswcs)
> > means that there must in fact be a difference between the tswcs of the
> > two cases.
> >
> > Hmm...
>
> So, this led me to a bug in my code... the file that was loading fast
> was constructed incorrectly :) (i.e. it should always have been
> painfully slow to load in data in the past). The problem is that SCUBA-2
> data are acquired with a system with a very jittery clock... so we need
> a time lookup table for each plane (a linear approximation won't do it
> unfortunately).
Oh dear, shame it wasn't the other way around!
> Is there a way I could launch GAIA so that it ignores the WCS information?
> (of course, I could hdelete it...).
Sorry seems not. I thought there might be a back door using the 3D access
system, but that falls down generating the backing image.
So you need to KAPPA:ERASE (hdelete I think not) the WCS.
Peter.
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