Standardising units and formats (and ref frames?) in transmission

[Alberto Micol]

Anita M. S. Richards wrote:
>
>
> On Mon, 18 May 2009, Alberto Micol wrote:
>
>> On 18 May 2009, at 11:58, Anita M. S. Richards wrote:
>>
>>> For example, I publish data in Galactic coordinates. If someone 
>>> wants to search in RA and Dec then a rough conversion is quite 
>>> quick, as long as they don;t mind getting back a region which may be 
>>> slightly larger than they asked for. But, we have had repeated 
>>> complaints from users in the past who want to search Galactic plane 
>>> surveys in Galactic coordinates, since a simple box (from an image 
>>> or catalogue) will give them what they want, but in RA and Dec it is 
>>> horrid.
>> As Francois puts it, a galactic search box is nothing else than
>> a equatorial box plus an angle. Not that horrid.
>
> It is not practical for images! And it is very non-linear for large 
> regions, taking sky curvature into account.
>
If the size of the box is given "on the sky" and not in coordinate space 
it should be fine.
But we can talk offline about the relevant math...


>>> Or, I want data with a certain spectral resolution which I specify 
>>> in wavelength unts, but the data are in frequency units with a 
>>> non-linear conversion - i.e., the spectal resolution at one end of 
>>> the bandpass is different from that at the other, if the units are 
>>> changed.
>> I'm asking for unification of units and formats: wavelengths always 
>> in meters, frequencies always in Hz. I was not pushing to have 
>> frequencies always in keV.  No complex conversions, no re-gridding, 
>> nothing subject
>> to interpretation, nothing that can corrupt the original piece of 
>> information.
>
> Ah, that is better - sorry I missed that!
>
> But why is it so difficult for us to apply SI prefixes, either?
>
For simplicity?
Anyway, it is not just matter of SI prefixes; this discussion started 
after having seen several comments
about various units and representations for TIME, and then later when 
even sexagesimal formats of
both time and spatial coordinates were discussed in the context of a 
VOTable... why making it more
complex than necessary?

> Thanks very much Alberto,
>
> a
And to you Anita,
Alberto