On Thu, 10 Aug 2006, David Berry wrote:
> Mark,
> The published form of FITS-WCS paper 2 does not allow any PVi_j
> keywords to be associated with the latitude (i.e. DEC) axis of a TAN
...
David,
I passed your comments to Rhys who passed them to Jonathan Irwin who
was responsible for this data in the first place. For your interest
here's what he said:
Jonathan Irwin wrote:
>
> Rhys Morris wrote:
>
> > HI Mike and Jonathan,
> >
> > I'm not sure who to contact regarding this, but I thought I would try
> > you two as a first guess.
> >
> > Some of the more recent 15x15 mosaics of IPHAS data have a WCS problem
> > which confuses gaia and ds9. The problem seems to first appear in the
> > 2336 RA series of data. Gaia thinks that part of the image is at an RA
> > of 11hours and other bits are correctly labelled as 23hrs, also gaia
> > cannot draw a grid on the image. Ds9 seems to get the RA readout
> > correct, but cannot draw a grid either. An example of an offending
> > image is below.
> >
> > ftp://ftp.star.bris.ac.uk/pub/rahm/2336+56_ha-r_mosaic.fit
> >
> > Our local FITS expert, Mark Taylor, had a look just in case it was a
> > gaia problem, and he points out that removing the
> >
> > PV2_3 = 220. /
> >
> > header appears to fix the problems on ds9 and gaia and may be the
> > cause of the problem.
>
> I think strictly this parameter has no meaning for the pure gnomonic
> projection implied by TAN, so it shouldn't matter if it's there or
> not. On the other hand it shouldn't be there because the code filters
> out WCS keywords, having read the docs it appears the CFITSIO
> incantation for doing so is very outdated with respect to the current
> WCS implementations, and doesn't understand this keyword.
>
> I'll try to remember to remove all these once the replacement set of
> mosaic files is generated, and I have updated the mosaic prog with
> some extra checks. Since it uses the contents of the primary HDU only
> there shouldn't even be WCS information in there!
Mark
--
Mark Taylor Astronomical Programmer Physics, Bristol University, UK
[log in to unmask] +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/
|