# Request for Modification for the UCD vocabulary towards UCDList v1.4

This page summarizes the steps for Modifications and Updates proposed in The UCD Maintenance workink draft .

The second (on going) iteration for the Request for modifications of UCD terms is summarized in the following content.

These terms are submitted for evaluation to the UCD science committee (see details in the Maintenance Specification document).

# UCDList v1.4 Request For Modifications, from May 2018 to Oct 2018

## Proposed UCD: stat.histogram

Use Case: A column contains not a single value but a distribution-like entity. For an example, run a query like

select
gavo_histogram(phot_g_mean_mag, 5, 15, 10) as dist,
round(100/parallax) as bin
from tgas.main
where parallax>5
group by bin


on the TAP service http://dc.g-vo.org/tap and inspect the dist column.

Proposed Solution: a primary-only atom stat.histogram would work for this. In the example in the use case, the service could assign a UCD stat.distribution;pos.parallax to the dist column. Hence, we'd add a new line to the UCD list:

P|stat.histogram | An array-like object with counts or ratios in bins

A footnote like "This also includes simple nonparametric distributions" or similar would be appreciated.

-- MarkusDemleitner - 2018-05-09

### Discussion

The column dist from the example certainly cannot be annotated as pos.parallax, and while there is stat.likelihood, there is no indication that this is intended to cover collection of likelihoods. I argue the UCD system should allow a plausible annotation of the dist column. If so, it appears we need some new term.

This new term should, I think, cover simple binned aggregations as well as nonparametric distributions (in the sense of \sum_{x\in\Omega} P(x)=1) in order to have sufficient generality. Hence, I'd avoid stat.distribution, which would imply normalisation.

Also, stat.distribution (or something like that) might, some day, be useful to annotate a different thing that this would not cover: columns containing distributions in the sense of some representation of "a gaussian with mu=3 and sigma=0.3" or "a poisson distribution with lambda=0.2".

The discussion started on the semantics mailing list . see the starting point for this discussion here

The proposed term is considering an array element instead of a single value , usually considered for the quantity tagged by a UCD.

Note that the semantic tag does not describe any property of the array except its statistical definition of histogram.

### Decision

Examine more use cases where this UCD could be combined to check the P or Q status before approving addition

( -- IVOA.MireilleLouys - 2020-02-03)

### Further discussion

Being able to tell that a column contains a histogram could be useful. However, the use of the UCD only is not sufficient to describe that column. We suggest that the histogram column is connected to a <GROUP ... /> through a ref attribute. The GROUP should define the binsize, the number of bins and the lower / upper bounds of the histogram, with units. Example:

[...]
<GROUP ID='histogram'>
<PARAM name='lower_bound' value=5 unit='' ucd='phot.mag;em.opt;stat;mean'/>
<PARAM name='upper_bound' value=15 unit='' ucd='phot.mag;em.opt;stat;mean'/>
<PARAM name='bin_count' value=10 unit='' ucd='meta.number'/>
<PARAM name='bin_size' value=1 unit='' ucd=''/>
</GROUP>
[...]
<FIELD ID='dist' datatype='int', ucd='stat.histogram;phot.mag;em.opt;stat;mean' ref='histogram' arraysize='*'/>
[...]

The result of the proposed query can't be used out of context, since the histogram properties are not described.

This is beyond the scope of Semantics/UCD, but this shows that we have to be cautious and may be propose a Note on how to deal with histograms in VOTable columns.

-- BaptisteCecconi - 2020-02-06

Previous iteration for the Request for modifications of UCD terms is summarized in the following page. ( click the link)

# UCDList v1.3 - from May 2017 to Feb 2018

Pending concepts considered in previous iteration waiting for more examples and use-case update

###### Concept: shape of planetary objects.

pos.rotation

pos.Euler.Angle

Concept : orbital parameters

Concept : 3D rotation parameters

# Request for Modification for the UCD list

This page is proposed in the new process for UCDs update discussed at the Interop meeting in Shanghai in May 2017. The new Note Maintenance for UCD specification mentions the details of the updating process. When a new UCD term seems necessary to include in the UCD list, a record describing the request for addition can be expressed as followed : new term proposed, rationale, example of usage, etc , as show in the list below.

The term is then disussed within the maintenance committee and the semantics working group and answers from the maintenance committee is given within 1 month.

Every 6 months the list of proposed changes are examined by the TCG and the validated changes are ingested in the new version of Endorsed Note for the UCD1+ list of terms.

##### Proposals from Solar and Planetary community ( B. Cecconi et al.)

#concept : electric current density
family: plasma environement
proposal: phys.flux ; phys.charge
requires : phys.charge with definition : Electric charge and tag : Q

#concept : electric current density
family: plasma environement
proposal: phys.flux ; phys.charge
requires : phys.charge with definition : Electric charge and tag : Q

##answer we understood the need for two concepts : electric current density and electric charge proposal for update:

add Q | phys.electCharge | Related to Electric charge
add Q | phys.current | Electric current
add Q | phys.current.density | Electric current density

benefits : introduces phys.current; this definition is more focused on the requested concept --> implies better assignment

#concept : Incidence
family: Observation geometry ; Illumination conditions
proposal: pos.incidenceAng
requires :
definition : Incidence angle
tag : Q

#concept: Emergence angle
family: Observation geometry ; Illumination conditions

proposal: pos.emergenceAng
definition : Emergence angle
tag : Q

#concept:Azimuth angle
proposal: pos.azimuthAng
definition : Azimuthal angle
tag : Q

proposal: pos.cylindrical
family : SSIG coordinates systems
rationale: no such coordinate branch in the UCD tree yet
definition : Cylindrical coordinates
tag : S

proposal: pos.cylindrical.r
requires :pos.cylindrical
definition : Cylindrical coordinate (radial distance from z-axis)
tag : Q

proposal: pos.cylindrical.th
definition : Cylindrical coordinate (Azimuthal angle around z-axis)
tag : Q

proposal: pos.cylindrical.z
definition : Cylindrical coordinate (height from reference plane)
tag : Q

#concept Spherical Coordinates

proposal: pos.spherical
Rationale: not present in UCD tree definition : spherical coordinates
tag : S

proposal: pos.spherical.r
definition : spherical coordinate (radial distance from origin)
tag : Q

proposal: pos.spherical.th
definition : spherical coordinate (colatitude angle)
tag : Q

proposal: pos.spherical.ph
definition : spherical coordinate (Azimuth angle)
tag : Q

#concept : orbital parameters
%Comment perifocal "src.orbital.periastron" exists but is slightly different
%Comment periapsis : check variation in meaning
proposal: src.orbital.periapsis
definition : minimal distance to the center of mass for an orbit
tag : P

#concept : rotation params
proposal: pos.rotation
definition : Relative to rotation
tag : S

proposal: pos.rotation.eulerAngle
definition : Euler angles vector
tag : V

proposal: pos.rotation.quaternion
definition : rotation quaternion vector
tag : V

proposal: pos.rotation.matrix
definition : rotation matrix
tag : V

proposal: pos.rotation.axis
definition : rotation axis vector
tag : V

#concept: spatial resolution

rationale: linear resolution on cartesian or linear spatial axis as opposed to angular resolution
proposal: pos.resolution
definition : Spatial linear resolution (not angular)
tag : Q

%heliocentric coordinates
longitude and latitude can be expressed as
proposal: pos.bodyrc.lon;pos.heliocentric
proposal: pos.bodyrc.lat;pos.heliocentric
% induced changes in assign tool: if heliocentric, or centric except geocentric , --> not earth .... change token

proposal: meta.checksum

rationale: to check integrity of data
definition : numerical signature of digital data
tag : Q

proposal: time.update
suggestion : add update in the definition of this ucd
_##answer agreed change token in the assigning tool _

# spectroscopic measures
#concept : reflectance

proposal: phys.reflectance
rationale : diff from albedo
% annotation master : to check ; consequence : change definition to albedo and remove reflectance
% | phys.albedo | Albedo or reflectance
derived usage :

proposal: phys.reflectance.bidirectional
definition : bidirectional reflectance
tag : Q

proposal: phys.brdf
rationale : specific term as much as psf for the community
definition : bidirectional reflectance distribution function
tag: Q

proposal: phys.reflectance.factor
definition : reflectance normalized per direction cosine of incidence angle ??
tag : Q

##answer add Q | phys.reflectance.factor | reflectance normalized per direction cosine of incidence angle

nb : check relevance and possible ambiguity with radiance factor...

%for normalized reflectance concept
proposal arith.ratio;phys.reflectance
definition : reflectance normalized per reflectance at one wavelength

#shape of planetary objects

this is used to represent the 3D shape of object: a 3D lattice

proposal: phys.shape
definition : 3D shape of a object
tag : Q
usage : phys.shape;meta.modelled for a 3D shape model
usage : phys.shape;pos.bodyrc.alt for elevation or terrain model (distribution of altitude on top of a reference ellipsoid or geoid )

_##discussion: postponed until a real case appears

# spectral polarization data
#concept :spatial matrix
rationale: helps to identify or characterize measurement type

_##discussion: postponed until a real case appears

proposal: phys.polarization.coherenceMatrix
definition: coherence matrix of radio signals
usage phys.polarisation.coherenceMatrix;instr
tag:Q

##answer add Q | phys.polarization.coherency | Matrix of the correlation between components of electromagnetic waves

not compatible to instr branch in the UCD tree

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