IVOA Web>IvoaSemantics>UCDList_1-3_RFM (2019-10-07, BaptisteCecconi)

Request for Modification for the UCD List v1.3 - from May 2017 to Feb 2018

This page is proposed in the new process for UCDs update discussed at the Interop meeting in Shanghai in May 2017.

As mentionned in the Maintenance for UCD specification we are adopting the following process. When a new UCD term seems necessary to ibe included 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 Proposed RFMs section below.

The term is then discussed 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.

Accepted RFMs

addition Q | phys.electCharge | Electric charge

addition Q | phys.current | Electric current

addition Q | phys.current.density | Electric current density

addition Q | pos.incidenceAng | Incidence angle of optical ray on an interface

addition Q | pos.emergenceAng | Emergence angle of optical ray on an interface

addition Q | pos.azimuth | azimuthal angle in a generic reference plane

addition Q | phys.reflectance | Radiance factor (received radiance divided by input radiance)

addition Q | phys.reflectance.bidirectional | Bidirectional reflectance

addition Q | phys.reflectance.bidirectional.df | Bidirectional reflectance distribution function

addition Q | phys.reflectance.factor | Reflectance normalized per direction cosine of incidence angle

addition S | pos.cylindrical |Related to cylindrical coordinates

addition Q | pos.cylindrical.r | Radial distance from z-axis (cylindrical coordinates)

addition Q | pos.cylindrical.azi | Azimuthal angle around z-axis (cylindrical coordinates)

addition Q | pos.cylindrical.z | Height or altitude from reference plane (cylindrical coordinates)

addition S | pos.spherical | Related to spherical coordinates

addition Q | pos.spherical.r | Radial distance or radius (spherical coordinates)

addition Q | pos.spherical.colat |Polar or Colatitude angle (spherical coordinates)

addition Q | pos.spherical.azi | Azimuthal angle (spherical coordinates)

addition Q | pos.resolution | Spatial linear resolution (not angular)

addition S | pos.bodycentric | Body-centric related coordinate

addition S | pos.bodygraphic | Body-graphic related coordinate

addition Q | meta.checksum | Numerical signature of digital data

addition Q | phys.polarization.coherency | Matrix of the correlation between components of an electromagnetic wave

The terms discussed and proposed for endorsement by the TCG are described in the EN-UCDlist-1.4-20180523 document ( in progress).

Rejected RFMs

Terms not fully discussed and agreed on have been postponed to the next iteration.
pos.rotation, pos.euleraAngle, pos.quaternion, ...
pos.heliocentric, pos.heliographic, etc .. postponed for better understanding : should consider the possibility of combination with other existing UCD .
Proposed RFMs

Here are the proposed terms with their proposal , discussion part and the status of agreement for addition of a UCD term or modification.

Proposals from Solar and Planetary community ( B. Cecconi, S. Erard et al.)

Concept family : electric charge and current

Family : plasma environment
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:

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

Concept family: Observation geometry ; Illumination conditions

Case:
- Representation of the various angles : Explained in paper https://doi.org/10.1016/j.pss.2015.06.004
- See figure attached here
- theta_i = Incidence Angle, theta_e = Emergence Angle, alpha = Phase Angle
- The angle phi (azimuth) is not required for illumination condition description (and we already have a UCD for this) from Baptiste Cecconi
Rationale: -from B. Cecconi - 06 July 2017 - see semantics list for the email threads
- In planetary sciences ... our use cases are the following:
- In EPNcore, the illumination conditions are search parameters, we have 6 separate columns for the min/max values of those 3 angles.
- For planetary images or spectra, the product metadata must contain the observation geometry, and those 3 angles are to be there, altogether.

Concept: Incidence angle

Proposal: pos.incidenceAng
Requires:
- definition : Incidence angle
- tag : Q
preliminary answer proposed: pos.posAng.incidence with definition : "Angle of incidence of a vector e.g illumination vector"
Discussion: There is a debate about this (S.Erard): incidence and emergence are physical angles of an optical ray on an interface / can be like pos.phaseAng; then it could logically be hooked under pos directly , as pos.phaseAng
answer: This is understood that we deal here with generic optical angles.

add Q | pos.incidenceAng | Incidence angle of optical ray on an interface

Concept: Emergence angle

proposal: pos.emergenceAng
Requires:
- definition : Emergence angle
- tag : Q
Answer: see discussion about incidence angle

add Q | pos.emergenceAng | Emergence angle of optical ray on an interface

Concept: Azimuth angle

Proposal: pos.azimuthAng
Requires:
- definition : Azimuthal angle
- tag : Q
Discussion: azimuthal angle is already defined in the ucd tree by:
- pos.az.azi exists but implies an alt-azimuthal ccordinate system.
Answer: azimuth already means 'angle'. We select pos.azimuth instead of pos.azimuthalAng ( shorter and self explaining)

add Q | pos.azimuth | azimuthal angle in a generic reference plane

Concept family: spectroscopic measures

Concept : radiance

Proposal: definition of phot.radiance is not completely adequate. It should be radiant power from the source per unit area (of source) and unit solid angle
Discussion: TBD

Concept : reflectance

Reflectances are relative quantities comparing input radiance or flux to the observed radiance, with various adimensional nomalization, so that their units can't be used for decide which actual physical quantity is shared or plotted. As current spectral analysis tools are using UCDs to decide how to combine data from various sources, there is a need for high level descriptors to sort out the most obvious kinds of normalization of processing. Without this, comparisions between dataset may lead to meaningless results.

proposal: phys.reflectance
rationale: different from albedo, which is valid at a given wavelength or frequency.
definition: This is a radiance factor: observed radiance divided by input radiance. This quantity derives from the surface or interface properties.
annotation master : to check ; consequence : change definition to albedo and remove reflectance
- | phys.albedo | Albedo or reflectance
Discussion: it is preferable to add a new term
Possible derived usage : Radiance Factor : arith.factor;phys.reflectance
Answer: the reflectance term is added.

add Q | phys.reflectance | Radiance factor (received radiance divided by input radiance)

Proposal: phys.reflectance.I_over_F
Rationale: This a specific measured reflectance, which may include the thermal emission of the body. This is defined as the observed radiance, divided by the input illumination flux (solar flux for planetary bodies). No correction for the black body emission is done on this quantity.
Discussion: open

Proposal: phys.reflectance.bidirectional
Definition: bidirectional reflectance
- tag : Q
Discussion:The current accepted short name is bidir
Answer: add new term

add Q | phys.reflectance.bidirectional | Bidirectional reflectance

Proposal: phys.brdf
Definition: bidirectional reflectance distribution function
- tag: Q
Discussion: check if phys.reflectance.bidirectional;instr.det.psf would do ?
- no, this is specific to normalization
Answer: add new term (the current accepted short name is BRDF )

add Q | phys.reflectance.bidirectional.df | Bidirectional reflectance distribution function

Proposal: phys.reflectance.factor
Definition: reflectance normalized per direction cosine of incidence angle ??
- tag : Q
Answer: add new term

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

Concept family: Coordinate frames

Concept : Cylindrical coordinates

Proposal: pos.cylindrical
Rationale : SSIG coordinates systems. No such coordinate branch in the UCD tree yet.
Definition : Cylindrical coordinates
- tag : S
Answer: add new term

add S |pos.cylindrical |Related to cylindrical coordinates

Proposal: pos.cylindrical.r
Requires :pos.cylindrical
Definition : Cylindrical coordinate (radial distance from z-axis)
- tag : Q
Answer: add new term

add Q | pos.cylindrical.r | Radial distance from z-axis (cylindrical coordinates)

Proposal: pos.cylindrical.th
Definition : Cylindrical coordinate (Azimuthal angle around z-axis)
- tag : Q
Discussion The conventions for the name of the angles varies : see http://mathworld.wolfram.com/CylindricalCoordinates.html prefered azi instead of th
Answer: add new term

add Q | pos.cylindrical.azi | Azimuthal angle around z-axis (cylindrical coordinates)

Proposal: pos.cylindrical.z
Definition : Cylindrical coordinate (height from reference plane)
- tag : Q
Answer: add new term

add Q | pos.cylindrical.z | Height or altitude from reference plane (cylindrical coordinates)

NB: less ambiguous as for angle names

Concept: Spherical Coordinates

Proposal: pos.spherical
Rationale: not present in UCD tree definition : spherical coordinates
- tag : S
Answer: add new term

add S | pos.spherical | Related to spherical coordinates

Proposal: pos.spherical.r
Definition : spherical coordinate (radial distance from origin)
- tag : Q
Answer: add new term

add Q | pos.spherical.r | Radial distance or radius (spherical coordinates)

Proposal: pos.spherical.th
definition : spherical coordinate (colatitude angle)
- tag : Q
Answer: add new term
Discussion: same as for cylindrical : various angle names depending on definitions ( http://mathworld.wolfram.com/SphericalCoordinates.html )
proposed to use the physical name for this angle : colatitude to avoid any notation dependency/ambiguity

add Q | pos.spherical.colat |Polar or Colatitude angle (spherical coordinates)

Proposal: pos.spherical.ph
definition : spherical coordinate (Azimuth angle)
- tag : Q
Answer: add new term

add Q | pos.spherical.azi | Azimuthal angle (spherical coordinates)

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
Answer discussion postponed not yet decided

Concept : rotation params for 3D parameters

Discussion pos. is the right branch to hook these rotation concepts.

pos.wcs exist for 2D transformation ;

pos.rotation will handle the 3D case --> propose pos.rotation3d_

Theses parameters will be used soon with real data .

Answer: We decide to delay the addition and will consider several examples

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

Proposal : pos.resolution
Rationale : linear resolution on cartesian or linear spatial axis as opposed to angular resolution
Definition : Spatial linear resolution (not angular)
- tag : Q
Answer: add new term

add Q | pos.resolution | Spatial linear resolution (not angular)

Concept: heliocentric coordinates

Discussion longitude and latitude can be expressed in the heliocentric coordinate system
Proposal : pos.bodyrc.lon;pos.heliocentric pos.bodyrc.lat;pos.heliocentric

% induced changes in assign tool: if heliocentric, or centric except geocentric , --> not earth .... change token

Decision : agreed to modify assigning tool - done
Discussion : In body-centric coordinates, longitudes are defined from sub-observer point, while body-graphic coordinates are defined from a standard body reference frame

TODO: VESPA team to check consistency between heliocentric and planetocentric definitions

Answer: add new term

add S | pos.bodycentric | Body-centric related coordinate

add S | pos.bodygraphic | Body-graphic related coordinate

Metadata branch

Concept: checksum

Proposal: meta.checksum
rationale : to check integrity of data
definition : numerical signature of digital data
- tag : Q
Answer: add new term

add Q | meta.checksum | Numerical signature of digital data

Concept: modification date of a dataset

proposal: time.update
definition : modification date for a dataset
discussion :time.processing already exists and can be used here . only the definition of the ucd term to be modified

??? update of the definition in the UCD list

Other items

Concept: shape of planetary objects

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

proposal : phys.shape
definition : 3D shape of an object
- tag : Q
Rationale : consider usage like phys.shape;meta.modelled for a 3D shape model, or phys.shape;pos.bodyrc.alt for elevation or terrain model (distribution of altitude on top of a reference ellipsoid or geoid )
Answer discussion: postponed until a real case is met