[fitswcs] WCS documents

[Stephen Walton]

I cannot pretend to speak for everyone, but my quietude has been at least
in part to incomplete understanding of all the issues involved.  I am
curious about the current discussion:  I _think_ it is in response to the
IRAF group's suggestion (quoting from their Web site): "we propose that
the WCS dimension be given by the highest value of the axis in any CTYPE
keyword, and that this value be permitted to be greater than the value of
NAXIS (a WCSDIM keyword could also be added to make this distinction more
apparent, but this is not necessary)."  As I understand it, this is to
allow subimages to carry along WCS information correctly.

I am afraid I don't get this.  If I have a 15 by 17 by 12 spatial by
spectral by spatial image, let's say, and I copy the portion
[1:15,11,1:12] to another image, most software I know of would create a 15
by 12 image as output, not a 15 by 1 by 12 image.  If said software also
simply copied the WCS with no checking, then there would be a mismatch;
further processing would associate the second WCS component of the
original image with the second dimension of the new image, rather than
with the third.  I can't see how the proposal quoted above, with or
without a WCSDIM/WCSAXES keyword, would help.

Bob, would you care to elaborate on some of the practical problems viz a
viz 'radio-optical interoperability' you ran into recently?

Steve

-- 
Stephen Walton, Professor of Physics and Astronomy,
California State University, Northridge
stephen.walton at csun.edu