On Fri, 21 Apr 2006, Rob Seaman wrote:
> > most trig functions need radians.
>
> Have been helping my daughter with her HS trig. Her textbook spends
> equal time between radians ("natural" units) and degrees (unnatural
> Babylonian units). Whether computer algorithms and languages prefer
> radians is an implementation detail. I find it revealing that we
> aren't arguing about HMS on the one hand and radians on the other,
> but rather about two different Babylonian variations (HMS versus
> degrees).
The reason for that focus in this debate is that VOTable already has machinery (the "unit" attribute) to work out what is meant if a column is specified in (numeric) radians or degrees, but doesn't if it's specified as (string) sexagesimals.
> Mark wrote:
> > The lexical analysis is not the problem, it's knowing what lexical
> > analysis you have to do - there is not a straightforward algorithm
> > for the mapping "string -> number" but there is for the mapping
> > "string-which-is-in-iso8601-format -> number".
> > All I'm proposing is a way of inserting hints about this.
>
> A feature is either required or it is not. What is the value to
> VOTable (or VOEvent, etc.) of a hint or pragma if tables are not
> required to use the feature? Applications will still have to
> heuristically select an appropriate lexical mapping.
I'd answer this by drawing the comparison with existing FIELD attributes such as ucd, unit, utype. Applications are not required to treat a column in any special way because it has the attribute ucd="phot.flux.bol", but it is there as additional information for those applications which understand that semantic hint. Similarly, some applications don't need to perform any lexical mapping, for instance those which only want to present the output to the user in a string format, but other applications, such as those which wish to calculate statistics, will find it useful.
Mark
-- Mark Taylor Astronomical Programmer Physics, Bristol University, UK m.b.taylor@bris.ac.uk +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/Received on 2006-04-24Z11:55:32