[fitswcs] -TAB progress report

[Mark Calabretta]

On Wed 2004/12/22 14:05:30 PDT, Eric Greisen wrote
in a message to: Mark Calabretta <mcalabre at atnf.csiro.au>
and copied to: fitswcs at nrao.edu

Hi Eric,

>    The choice of tabini for a s.r. name may give AIPS a pain if we

Hmmm, good old TABINI - that brings back memories!  The name follows a
pattern set in the rest of WCSLIB and it would be a pity to break it.
AIPS TABINI should become tabini_ but there could be a problem with the
WCSLIB FORTRAN wrappers.  An appropriate solution might be to allow it
to be #define'd to something else in WCSLIB so AIPS can handle it as a
preprocessor define.  Sound OK?

>      Mark, why is 2-D linear interpolation so hard for you?  I

It's because you have to iterate over M (possibly > 2) array indices in
only one loop.  You do this by binary indexing - it won't be obvious to
everyone.

>will find a place in the paper to write the thing out in glorious
>detail but it will be a multi-line mess obscuring the simplicity of
>the concept.

Please don't!

>If anyone can find a place in Paper III and a suggested wording I will
>accept it.  The opening sentence in -TAB says coordinate well defined
>which a singularity is not...

Best left to Paper IV I think.  I was trying to map the neighbourhood of
a singularity, not the singularity itself.  At first glance it did look
like it should be possible because the coordinate grid was composed
solely of straight lines convergent on the singularity; I was a bit
surprised at how far it fell short.  However, this is just the nature of
linear-interpolation in 2-D and should not affect Paper III; it's why
we have to have a Paper IV.

Cheers, Mark