On Tue 2005/09/06 11:06:30 MST, Tom Jarrett wrote
in a message to: fitsbits@xxxxxxxxxxxxxxxxx
and copied to:
>is correct. I would greatly appreciate it if someone out there has a look
>at one of our cubes, checking out the FITS header and the
>CTYPE3 = 'WAVE-TAB' /Wavelength
>definition. Please let me know if you find a problem or potential
>problem with what we have done. Here is the sample, it is a spectral map
It's basically correct but there are a few things you need to fix:
1) According to Paper I, if any CDi_ja cards are given then those not
given all default to zero. Therefore CD3_3 == 0 and your matrix is
2) In general, the coordinate array is of dimensionality M+1 with axis
lengths (M, K1, K2,...) which are to be recorded in a TDIMn card.
Although your table is 1-dimensional (M == 1), the coordinate array
is formally considered to be 2-dimensional though with a degenerate
first axis, and you should write the TDIMn card.
3) CRPIX3 and CRVAL3 are both omitted from the header which is bad form.
Also, note that -TAB does not allow extrapolation; although it could be
accomodated for non-degenerate 1-D tables with default indexing (perhaps
it should be) it can't easily be generalized to higher dimensions or
Hence, your -TAB only defines wavelengths for pixel coords between 1.0
and NAXIS3. If you want to compute wavelengths at pixel coordinate 0.5
or NAXIS3+0.5 you'll need to extend the coordinate array slightly and
adjust CRPIX3 and/or CRVAL3 accordingly.