[fitswcs] Units along spectral axes

[William Thompson]

David Berry wrote:

 > There was quite a bit of discussion of the handling of units on the IVOA
 > lists a few months ago. The practical problem is that there is an awful
 > lot of existing data out there which uses "nearly but not quite FITS"
 > units syntax, and most software systems will need to be able to
 > interpret these units variations. There were three basic approaches
 > disccused on the IVOA lists:
 > > 1) Get everyone to change all their existing data archives to
 > correct non-standard units strings to FITS-WCS paper I syntax. Not
 > practical!

	...

I doubt that those existing archives use the "4-3" notation of Paper III to 
implement non-linear projections of the coordinates.  My main concern is making 
the projection equations work out correctly--the issue of interpreting the data 
is another matter.

I will augment my parser to handle the most obvious potential units variations.

William Thompson