coords
This model defines objects which describe the coordinate space, coordinates within that space, and frames, which provide additional metadata regarding the origin, orientation, etc, of the coordinate space. The model also defines a coordinate system, bundling frames into associated groups.
Astronomical Coordinates and Coordinate Systems
Arnold Rots, Mark Cresitello-Dittmar, Omar Laurino
1.0
0
2020-03-13T10:54:42
ivoa
http://www.ivoa.net/xml/VODML/20180519/IVOA-v1.0.vo-dml.xml
http://volute.g-vo.org/svn/trunk/projects/dm/vo-dml/models/ivoa/vo-dml/IVOA-v1.0.html
Epoch
Epoch
We define epoch as a primitive data type with the expected form "<type><year>" where type = "J" or "B" for Julian or Besselian respectively, and year is expressed as a decimal year. e.g.: "B1950", "J2000.0"
Handedness
Handedness
The handedness of a coordinate space. For most cases, this will be a fixed value in the specification of the coordinate space. We provide this element to allow this flexibility when needed. In this document, it is used in the Pixel domain.
Handedness.left
left
positive x and y axes point right and up, the positive z axis points inward
Handedness.right
right
positive x and y axes point right and up, the positive z axis points outward
PolStateEnum
PolStateEnum
Polarization states: Stokes, Circular, Linear and Vector states
PolStateEnum.I
I
TODO : Missing description : please, update your UML model asap.
PolStateEnum.Q
Q
TODO : Missing description : please, update your UML model asap.
PolStateEnum.U
U
TODO : Missing description : please, update your UML model asap.
PolStateEnum.V
V
TODO : Missing description : please, update your UML model asap.
PolStateEnum.RR
RR
TODO : Missing description : please, update your UML model asap.
PolStateEnum.LL
LL
TODO : Missing description : please, update your UML model asap.
PolStateEnum.RL
RL
TODO : Missing description : please, update your UML model asap.
PolStateEnum.LR
LR
TODO : Missing description : please, update your UML model asap.
PolStateEnum.XX
XX
TODO : Missing description : please, update your UML model asap.
PolStateEnum.YY
YY
TODO : Missing description : please, update your UML model asap.
PolStateEnum.XY
XY
TODO : Missing description : please, update your UML model asap.
PolStateEnum.YX
YX
TODO : Missing description : please, update your UML model asap.
PolStateEnum.PF
PF
TODO : Missing description : please, update your UML model asap.
PolStateEnum.PP
PP
TODO : Missing description : please, update your UML model asap.
PolStateEnum.PA
PA
TODO : Missing description : please, update your UML model asap.
Coordinate
Coordinate
Abstract base class for the Coordinate data types which represent an absolute location within a coordinate space. Coordinates MUST refer to a coordinate system, providing additional metadata relevant to interpreting the coordinate value, and its representation.
Coordinate.coordSys
coordSys
Provided additional metadata relevant to interpreting the coordinate value; for example, the spatial reference position, or time scale, axis descriptions.
coords:CoordSys
1
1
BinnedCoordinate
BinnedCoordinate
Coordinate value type specifically intended for binned data (e.g.: pixel indexes).
coords:Coordinate
BinnedCoordinate.cval
cval
The binned coordinate value, expressed as an integer. e.g.: bin number, pixel index.
ivoa:integer
1
1
PixelIndex
PixelIndex
Specialized BinnedCoordinate for the pixel domain for a 1-dimensional pixel index. PixelIndex MUST refer to a PixelCoordSystem.
coords:BinnedCoordinate
PhysicalCoordinate
PhysicalCoordinate
The most common type of coordinate value. This type is appropriate for any data whose values can be described by an ivoa:Quantity (numeric, with unit).
coords:Coordinate
PhysicalCoordinate.cval
cval
This coordinate MUST contain a value expressed as an ivoa:Quantity.
ivoa:Quantity
1
1
Point
Point
Multi-dimensional spatial coordinate. The Point MUST refer to a spatial coordinate system (SpaceSys). The coordinate values map, in order, to the axes described by the associated CoordSpace. Values for unused/undefined dimensions need not be provided.
coords:Coordinate
coords:Coordinate.coordSys
coords:SpaceSys
Point.axis1
axis1
Coordinate value along the first axis of the associated coordinate space, expressed as an ivoa:Quantity.
ivoa:Quantity
0
1
Point.axis2
axis2
Coordinate value along the second axis of the associated coordinate space, expressed as an ivoa:Quantity.
ivoa:Quantity
0
1
Point.axis3
axis3
Coordinate value along the third axis of the associated coordinate space, expressed as an ivoa:Quantity.
ivoa:Quantity
0
1
TimeStamp
TimeStamp
This is the abstract basis for a set of simple time domain coordinates which are expected to accommodate the vast majority of use cases. All TimeStamps, by definition, exist in a standard 1-D coordinate space, with domainMin|Max of +/-Infinity. All TimeStamps MUST refer to an appropriate TimeSys.
coords:Coordinate
coords:Coordinate.coordSys
coords:TimeSys
TimeOffset
TimeOffset
Time is given as an offset from a specific point in time (time0).
coords:TimeStamp
TimeOffset.time
time
The TimeOffset coordinate value.
ivoa:RealQuantity
1
1
TimeOffset.time0
time0
The reference time from which the offset is calculated. This MUST be given as a TimeInstant (e.g.: JD, MJD, ISOTime).
coords:TimeInstant
1
1
TimeInstant
TimeInstant
TimeStamps which specify a specific instant in time. We define three subtypes (ISOTime, JD, MJD), which allow users to explicitly identify the representation and interpretation of the TimeInstant.
coords:TimeStamp
JD
JD
Extension of TimeInstant for time expressed in Julian days. Note that JD does not properly specify a time stamp unless it is related to a time scale and reference position. Precision can easily become an issue with JD, as the numbers tend to be large.
coords:TimeInstant
JD.date
date
The JD coordinate value. JD dates are dimensionless, with implied units in days.
ivoa:real
1
1
MJD
MJD
Extension of TimeInstant for time expressed in Modified Julian Days. T(MJD) = T(JD) - 2400000.5.
coords:TimeInstant
MJD.date
date
The MJD coordinate value. MJD dates are dimensionless, with implied units in days.
ivoa:real
1
1
ISOTime
ISOTime
Extension of TimeInstant for time expressed as a structured datetime string.
The string representation of a datetime value should follow the FITS convention for representing dates (Hanish and Farris et al, 2001). The FITS standard is effectively ISO8601 format without the 'Z' tag to indicate UTC: YYYY-MM-DD['T'hh:mm:ss[.SSS]]. The TimeScale is provided in the associated TimeFrame.
coords:TimeInstant
ISOTime.date
date
The ISOTime coordinate value.
ivoa:datetime
1
1
PolCoordinate
PolCoordinate
Abstract head of the polarization coordinate types. Current use cases only require support for discrete polarization states, however, we include this head class to facilitate extension for other types (eg: polarization fraction and angle).
coords:Coordinate
PolState
PolState
Coordinate type for discrete polarization states.
coords:PolCoordinate
PolState.cval
cval
The coordinate value MUST be from the PolStateEnum enumerated set.
coords:PolStateEnum
1
1
RefLocation
RefLocation
RefLocation defines the origin of the spatial coordinate space. This location is represented either by a standard reference position (for which the absolute location in phase space is known by definition), or a specified point in another Spatial frame. This object is used as the origin of the SpaceFrame here, but also to specify the Spatial Reference Position (refPosition) associated with other domain Frames. For example, in the Time domain, the Spatial Reference Position indicates that the 'time' values are the time that the 'event' occured at that location, which might be different from the detector location.
StdRefLocation
StdRefLocation
An absolute a-priori known location in phase space (position and velocity). Values are selected from the StdRefPosition vocabulary. Considering that the GEOCENTER is really the only place for which we know the absolute location at all times, all other locations require the specification of a planetary ephemeris. LSR[KD] are reserved for spectral and reshift frames. TOPOCENTER (location of the observer) is special in that it assumes that the observing location is available through other means (e.g. a geographic location or an orbit ephemeris). RELOCATABLE is available for simulations. UNKNOWN should only be used if absolutely necessary.
coords:RefLocation
StdRefLocation.position
position
Standard reference location. Values MUST be selected from the controlled vocabulary at the given URL.
ivoa:string
1
1
ReferencePosition
http://www.ivoa.net/rdf/refposition
CustomRefLocation
CustomRefLocation
A custom reference location in phase space (position and velocity). Position and velocity are given as coordinates with an associated SpaceFrame. An epoch MAY be provided to further refine the location.
coords:RefLocation
CustomRefLocation.epoch
epoch
Epoch for the reference location.
coords:Epoch
0
1
CustomRefLocation.position
position
The spatial coordinates of the reference location.
coords:Point
1
1
CustomRefLocation.velocity
velocity
The velocity of the reference location.
coords:Point
0
1
CoordSpace
CoordSpace
This object defines a domain space. i.e.: it describes the set of possible coordinate values.
CoordSpace.axis
axis
Describes an axis of the coordinate space.
coords:Axis
1
-1
Axis
Axis
The abstract parent class for all coordinate axis types. We provide concrete classes for the most common types of data, Continuous, Binned, and Discrete, but allow extension for other types as needed.
Axis.name
name
Freeform string, provides the name or label for the axis.
ivoa:string
0
1
ContinuousAxis
ContinuousAxis
Axis description for continuous data. This object describes the domain for a particular axis of the domain space. It allows for the specification of the legal domain range (min,max), and a flag indicating if the axis is cyclic.
coords:Axis
ContinuousAxis.domainMin
domainMin
Minimum extent of the axis domain space. If not provided, the domain space is considered to have no lower bound (-INFINITY).
ivoa:Quantity
0
1
ContinuousAxis.domainMax
domainMax
Maximum extent of the axis domain space. If not provided, the domain space is considered to have no upper bound (+INFINITY).
ivoa:Quantity
0
1
ContinuousAxis.cyclic
cyclic
Flag indicating if the axis is cyclic in nature. If not provided, it is assumed to be FALSE.
ivoa:boolean
0
1
BinnedAxis
BinnedAxis
Axis description for binned data, where values along the axis correspond to a bin number.
coords:Axis
BinnedAxis.length
length
The length, or number of bins, along the axis.
ivoa:nonnegativeInteger
1
1
DiscreteSetAxis
DiscreteSetAxis
Axis type specifically intended for enumerated coordinates. Since the content and nature of this axis type is heavily dependent on the use case, we define no additional metadata here. Extensions of this type may include additional metadata relevant to the particular use cases. For example, an extension could include the allowed set of values.
coords:Axis
CoordFrame
CoordFrame
This is the abstract, empty, base class for all coordinate frames. Coordinate frames provide metadata associated with the coordinate domain space. Typically, this will be related to the origin and orientation of the axes, but might include any metadata which pertains to the definition of the domain.
GenericFrame
GenericFrame
The generic coordinate frame is for cases where a domain-specific frame (e.g.: Space, Time), is not required, but the relevant reference metadata is still needed (e.g.: for Redshift or Spectral data)
coords:CoordFrame
GenericFrame.refPosition
refPosition
Spatial location in phase space (position and velocity) at which the observed value is considered to have been taken. This will typically be given by a standard reference position, but we allow for custom locations as well.
coords:RefLocation
1
1
GenericFrame.planetaryEphem
planetaryEphem
A planetary ephemeris MAY be provided, and SHOULD be provided whenever appropriate, to indicate which solar system ephemeris was used. If needed, but not provided, it is assumed to be "DE405"
ivoa:string
0
1
SpaceFrame
SpaceFrame
A SpaceFrame is specified by its reference frame (orientation), and a reference position (origin). Currently only standard reference frames are allowed. An equinox MUST be provided for pre-ICRS reference frames. A planetary ephemeris MAY be provided if relevant. If needed, but not provided, it is assumed to be "DE405".
coords:CoordFrame
SpaceFrame.refPosition
refPosition
The spatial location at which the coordinates are considered to have been determined. This model supports locations provided as either a standard reference position (e.g. GEOCENTER), or a coordinate specifying a custom location (e.g. long, lat, height ).
coords:RefLocation
1
1
SpaceFrame.spaceRefFrame
spaceRefFrame
The spatial reference frame. Values MUST be selected from the controlled vocabulary at the given URL.
ivoa:string
1
1
SpaceRefFrame
http://www.ivoa.net/rdf/refframe
SpaceFrame.equinox
equinox
Reference date for the frame, required for pre-ICRS reference frames.
coords:Epoch
0
1
SpaceFrame.planetaryEphem
planetaryEphem
Ephemeris file for solar system objects SHOULD be specified whenever relevant.
ivoa:string
0
1
TimeFrame
TimeFrame
A TimeFrame SHALL include a time scale and reference position. It MAY also include a reference direction.
coords:CoordFrame
TimeFrame.refPosition
refPosition
The spatial location at which the coordinate is considered to have been taken. This model supports locations provided as either a standard reference position (e.g. GEOCENTER), or a coordinate specifying a custom location (e.g. long, lat, height).
coords:RefLocation
1
1
TimeFrame.timescale
timescale
The time scale sets the reference frame. The value MUST be selected from the controlled vocabulary at the given URL.
ivoa:string
1
1
TimeScale
http://www.ivoa.net/rdf/timescale
TimeFrame.refDirection
refDirection
The reference direction is needed if the time stamps are transformed to a time frame with a different reference position. In those situations, the solar system ephemeris also comes into play. See: FITS WCS Paper IV for details, but in short: The reference direction, presumably the direction to the thing being observed, is used in conjunction with the reference position and planetary ephemeris to determine the correction applied for the path length change. To be fully useful, one also needs to know the location at which the observation was made ( i.e. the observatory location), which is not considered to be Frame metadata.
coords:RefLocation
0
1
AstroCoordSystem
AstroCoordSystem
The AstroCoordSystem object holds a collection of component coordinate system descriptions across all represented physical domains.
coords:CoordSys
AstroCoordSystem.coordSys
coordSys
Coordinate system description for each physical domain (Space, Time, etc).
coords:PhysicalCoordSys
1
-1
PixelCoordSystem
PixelCoordSystem
The PixelCoordSystem provides a complete description of the pixel coordinate space. It SHALL contain one PixelSpace instance describing each pixel axis.
coords:CoordSys
PixelCoordSystem.pixelSpace
pixelSpace
The pixel space completely defines the pixel coordinate axes. Each axis MUST be defined as a BinnedAxis type.
coords:PixelSpace
1
1
PixelSpace
PixelSpace
A PixelSpace SHALL include one or more BinnedAxis objects describing the pixel coordinate space. A handedness value MAY be provided to specify the relative orientation of the axes.
coords:CoordSpace
coords:CoordSpace.axis
coords:BinnedAxis
PixelSpace.handedness
handedness
Specifies the handedness of the coordinate space.
coords:Handedness
0
1
CoordSys
CoordSys
Abstract head of the coordinate system object tree.
PhysicalCoordSys
PhysicalCoordSys
Coordinate system description for any physical domain, such as Time, Space, Redshift, Temperature, Flux, etc.
coords:CoordSys
PhysicalCoordSys.coordSpace
coordSpace
Description of the coordinate space occupied by the property.
coords:PhysicalCoordSpace
0
1
PhysicalCoordSys.frame
frame
TODO : Missing description : please, update your UML model asap.
coords:CoordFrame
0
1
GenericSys
GenericSys
Specialized coordinate system for generic, one-dimensional domains not covered by other, more concrete objects. If a CoordSpace is not provided, it is assumed to be represented by a Standard 1-Dimensional Coordinate Space as described in Appendix B.
coords:PhysicalCoordSys
coords:PhysicalCoordSys.frame
coords:GenericFrame
SpaceSys
SpaceSys
Specialized coordinate system for the Spatial domain. This object SHOULD include an appropriate SpaceFrame. In Appendix B, we define two standard spatial coordinate space instances (Spherical and Cartesian), which may be referenced in serializations. If a CoordSpace is not provided, it is assumed to be represented by a Standard Spherical Coordinate Space.
coords:PhysicalCoordSys
coords:PhysicalCoordSys.frame
coords:SpaceFrame
TimeSys
TimeSys
Specialized coordinate system for the Temporal domain. This object SHOULD include an appropriate TimeFrame. If a CoordSpace is not provided, it is assumed to be represented by a Standard 1-Dimensional Coordinate Space as described in Appendix B.
coords:PhysicalCoordSys
coords:PhysicalCoordSys.frame
coords:TimeFrame
coords:PhysicalCoordSys.coordSpace
coords:GenericCoordSpace
PhysicalCoordSpace
PhysicalCoordSpace
Abstract head of coordinate spaces related to physical properties.
coords:CoordSpace
GenericCoordSpace
GenericCoordSpace
Generic, one-dimensional coordinate space suitable for use with most non-spatial properties. In Appendix B, we provide the description of a Standard 1D Coordinate Space instance which may be referenced in serializations.
coords:PhysicalCoordSpace
axis[1]
SphericalCoordSpace
SphericalCoordSpace
Spatial domain, three-dimensional spherical coordinate space. The particulars of the axis descriptions depend on the flavor of space being instantiated. In Appendix B., we provide a Standard Spherical Coordinate Space instance which applies to many Astronomical use cases. It provides the default space for SpaceSys instances, and may be referenced in serializations.
coords:PhysicalCoordSpace
axis[3]
coords:CoordSpace.axis
coords:ContinuousAxis
CartesianCoordSpace
CartesianCoordSpace
Spatial domain, three-dimensional cartesian coordinate space. The particulars of the axis descriptions depend on the physical constraints of the instance. In Appendix B, we provide the description of a Standard Cartesian Coordinate Space instance which applies to many Astronomical cases, and may be referenced in serializations.
coords:PhysicalCoordSpace
axis[1..3]
coords:CoordSpace.axis
coords:ContinuousAxis