Inputs for UCDs

[Stéphane Erard]

Dear all

Here are some comments I’ve collected since the last Interop Meeting about UCDs, in relationship with Planetary Science / coming EPNCore standard. 
Sorry for the short notice ;(

Cheers
Stéphane


Maps:
• At least a new pos.projection is required to introduce projection/mapping schemes (there is currently only a very specific pos.lambert). 

VOevents:
• UCDs are needed for VOevents properties


For reflected light measurements:

• Correct/clarify definition of reflectance in 2018 RFM sheet: 
add Q | phys.reflectance | Radiance factor (received radiance divided by input radiance)
=> Radiance factor is the same as I/F; in this case, this is divided by input irradiance (not radiance), i.e. by the solar flux.

• Correct/clarify brdf in 2018 sheet: 
addQ | phys.reflectance.bidirectional.df| Bidirectional reflectance distribution function

This UCD is very weird, would better be phys.reflectance.brdf (this is not a subset of .bidirectional, and dfl means nothing in this context while brdf is a common acronym)
definition: Ratio of radiance to incident normal solar flux

• Suggestion for reflectance in 2018 RFM sheet, to be corrected: 
for normalized reflectance concept: proposal arith.ratio;phys.reflectance 
definition : reflectance normalized per reflectance at one wavelength 
=> Should be arith.factor;phys.reflectance


Other UCDs:
• posAng is commonly mistaken for a generic UCD for angles (which does not exist), while it is specifically for position angles. 
=> Make definition more explicit (e.g., from Free dictionary: the direction in which one object lies relative to another on the celestial sphere, measured in degrees from north in an easterly direction)

• How do we handle hemispherically integrated quantities?

• arithm.ang could do as S to specify angular distributions

• Section 8, 2 (about pos section): 
"the angular size of an object is in this section, its linear size is in the phys section)"
But we have phys.angSize (with an unclear definition)  - should it be in pos then?

• On the same token, 
phys.angVeloc would look more consistent than phys.veloc.ang

• How do we specify an additive constant or offset? 
The only close match is arith.zp, which is context specific (for magnitude scales)
=> Enlarge the definition to any type of offset / additive constant?

• We have compiled a preliminary list of measured spectral quantities - get prepared for this ;)
In particular, a category phys.scattering seems required, see here: 
https://voparis-wiki.obspm.fr/display/VES/Lab+spectroscopy+extension
(Table 2, column 3 for proposals)


+ I’m not sure if this is for here, but I also noted:
• Clarify usage of inf / -inf / Nan in ADQL (should apparently exist, as per DALI - but do not)