UCD vocabulary revision : first iteration of the maintance procedure

[Stéphane Erard]

Le 23 mai 2018 à 10:31, Frederic V. Hessman <hessman at astro.physik.uni-goettingen.de> a écrit :

>>> Q | phys.reflectance.bidirectional | Bidirectional reflectance
>>> Q | phys.reflectance.bidirectional.df | Bidirectional reflectance distribution function
>> 
>> This one is a misunderstanding: "distribution function" is not a subtype of bidirectional reflectance (and has nothing to do with a probability distribution function). Instead, both bidirectional and brdf (= bidirectional reflectance distribution function) are subtypes of reflectance. brdf is a standard acronym in the interested community.
>> I suggest instead to have
>> Q | phys.reflectance.bidirectional | Bidirectional reflectance (as proposed)
>> Q | phys.reflectance.brdf | Bidirectional reflectance distribution function
>> If this is an issue, the first one has priority
> 
> I don't want to press the issue, but a distribution function is not a reflectance and has everything to do with probabilities in a generic sense, so a "bidirectional reflectance distribution function" must have everything to do with a PDF in the generic sense the UCDs are intended.  The normal uses of UCDs demand that the metadata context be multi-dimensional so that, e.g., the apps know a distribution function is a distribution function, no matter what it is a distribution of.
> 
> Rick
> 

There is no such thing as a "distribution function" in this case. There is a "Bidirectional reflectance distribution function" which has a precise definition (radiance referred to a certain estimate of the input flux). The name may be unfortunate, but it is standard; the "distribution" implied here is angular, not statistic, and it is not provided as a function (it is usually given only in a certain direction). The usual "Bidirectional reflectance" also has angular dependency.
As I said, we can drop this one if it is confusing.

Cheers,
Stéphane