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On 25/02/2008, David Berry <[log in to unmask]> wrote: > On 25/02/2008, Jaime Perea <[log in to unmask]> wrote: > > Ooops, > > > > Shame on me, first posting and it was a mistake in the To: field. > > > > Anyway, the problem is that SDSS spectra are log lambda spaced > > instead of lambda. Then a previous scrunch is needed to allow > > dipso to use those spectra. > > > Looking at the dipso code, it would have expected it to be able to > handle log spaced data succesfully. I'd be interested in looking at at > example SDSS spectrum to see why dipso has problems with the log > spacing. Can you point me at one? The problem is that the standard FITS-WCS headers do indeed describe a linear coordinate system. They are obviously lying :-) Presumably the correct WCS information is contained within some of the extra SDSS headers that are not part of the FITS-WCS standard. It would be possible of course to edit the headers to include standard FITS-WCS keywords describing the WCS, in which case DIPSO would corectly pick up the log axis. But if you are happy for the data to be resampled onto a linear axis, it is probably easier to scrunch the data using iraf as Jaime suggests. If you would prefer the data to retain its logarithmic spacing, then I can let you know how to edit the headers appropriately. David