vodmlid 
feature type 
description 

vodml:model 
This model defines objects and datatypes which represent 'measured' or 'determined' data. It associates a Coordinate (ie:
the determined value with associated physical context) with corresponding Error(s). As such, this model is at least the foundation
for representing the vast majority of the Astronomical data found in catalogs and data products.
We define here, several specialized classes which cover the most basic and common types, such as Position and Time. We also
provide a generic model which can accommodate virtually any data, but may require a bit more effort to fully describe the
coordinate metadata. Additional specializations, e.g. Flux, Magnitude, Luminosity, Pressure, Temperature, etc. may be added
to this model, or in other models focusing on particular domains or use cases.
We include a fairly simple Error model, describing errors as a 'shape' of uncertainty, and define a small set of commonly
occuring forms (e.g. Symmetrical, Bounds, Ellipsoid).

Asymmetrical1D 
dataType 
Uncertainty with different extent in the positive and negative directions from the associated Coordinate. 
Asymmetrical1D.minus 
attribute 
Extent in the negative axis direction. 
Asymmetrical1D.plus 
attribute 
Extent in the positive axis direction. 
Asymmetrical2D 
dataType 
2D Uncertainty with different extent in the positive and negative axis directions from the associated Coordinate. i.e.: an
offset rectangle.

Asymmetrical2D.minus 
attribute 
Extent in each negative axis direction. 
Asymmetrical2D.plus 
attribute 
Extent in each positive axis direction. 
Asymmetrical3D 
dataType 
3D Uncertainty with different extent in the positive and negative axis directions from the associated Coordinate. i.e.: an
offset box.

Asymmetrical3D.minus 
attribute 
Extent in each negative axis direction. 
Asymmetrical3D.plus 
attribute 
Extent in each positive axis direction. 
Bounds1D 
dataType 
Provide the edges of the uncertainty space. Rather than being relative to the associated Coordinate, these represent a range
within that Coordinate space.

Bounds1D.hiLimit 
attribute 
Upper limit of the uncertainty range. 
Bounds1D.loLimit 
attribute 
Lower limit of the uncertainty range. 
Bounds2D 
dataType 
Provide the edges of a 2D uncertainty space. Rather than being relative to the associated Coordinate, these represent ranges
along each axis of that Coordinate space.

Bounds2D.hiLimit 
attribute 
Upper edges of the uncertainty rectangle. 
Bounds2D.loLimit 
attribute 
Lower edges of the uncertainty rectangle. 
Bounds3D 
dataType 
Provide the edges of a 3D uncertainty space. Rather than being relative to the associated Coordinate, these represent ranges
along each axis of that Coordinate space.

Bounds3D.hiLimit 
attribute 
Upper edges of the uncertainty box. 
Bounds3D.loLimit 
attribute 
Lower edges of the uncertainty box. 
Ellipse 
dataType 
Elliptical uncertainty shape. 
Ellipse.posAngle 
attribute 
Position angle, counterclockwise from the positive direction of the first axis of the associated Coordinate. When used in
the spatial domain, the expectation is that the 'first axis' corresponds to the 'North Celestial Pole', and the second to
'East', thereby conforming to the IAU definition of the position angle direction being 'East of North'.

Ellipse.semiAxis 
attribute 
Extent of the semimajor and semiminor axes, provided in the order of the associated Coordinate axes. 
Ellipsoid 
dataType 
Ellipsoidal uncertainty shape. 
Ellipsoid.posAngle 
attribute 
Position angles
* counterclockwise from the positive direction of the first axis toward the second axis
* angle 'above' the plane of the first two axes of the associated Coordinate.
When used in the spatial domain, the expectation is that the 'first axis' corresponds to the 'North Celestial Pole', and the
second to 'East', thereby conforming to the IAU definition of the position angle direction being 'East of North'.

Ellipsoid.semiAxis 
attribute 
Extent of the semi axes, provided in the order of the associated Coordinate axes. 
Error 
objectType 
The Error class uses the Uncertainty types to describe measurement errors from various sources. 
Error.statError 
attribute 
Statistical error. The Uncertainty type MUST be dimensionally compatible with the associated Measure value. 
Error.sysError 
attribute 
Systematic error. The Uncertainty type MUST be dimensionally compatible with the associated Measure value. 
GenericMeasure 
objectType 
The most generic Measure class. This class may be used to represent data not covered by the specialized cases. 
GenericMeasure.coord 
attribute 
The measured coordinate value. 
Measure 
objectType 
Abstract base of Measure classes, associates a 'determined value' (Coordinate) with corresponding errors.
We associate the Error(s) with the full Measure, rather than the individual values, in order to support both correlated and
uncorrelated errors. In many cases with multidimensional data, the associated errors are correlated and must be considered
with the value set as a whole. One consequence of this approach is that there is a looser association between the Error dimensions
and the corresponding value dimension. We require that the Error content MUST be compatible with the value dimension and
nature (e.g. dimension, domain, units, etc).

Measure.error 
composition 
Measurement error. 
Polarization 
objectType 
Provides a complete description of a determined polarization state. Since the polarization coordinate is an enumerated type,
there can be no associated numerical error sources.

Polarization.coord 
attribute 
Determined polarization state. May be provided by any of the PolCoordValue subtypes. 
Position 
objectType 
Provides a complete description of a measured positional instant. 
Position.coord 
attribute 
The measured Position value. The Point coordinate supports 1,2, and 3dimensional cases. Details of the coordinate system
(space and frame), are associated with the Point.

ProperMotion 
objectType 
Proper motion represented as the velocity in Longitude and Latitude directions of a spherical coordinate space. The associated
SpaceFrame provides the details regarding the nature of the coordinate space (eg: Equatorial, Galactic, etc).

ProperMotion.lat 
attribute 
Velocity in angular distance per unit time along the Latitude axis. 
ProperMotion.lon 
attribute 
Velocity in angular distance per unit time along the Longitude axis. It is common, though not universal, practice to quote
longitudinal proper motion premultiplied by cos(lat) so that the magnitude of the quantity is not affected by its longitudinal
position. We do not constrain this value to one form or the other in this model, leaving it to be specified by the particular
usage thread.

Symmetrical 
dataType 
Symmetrical uncertainty, constant in all dimensions and directions from the associated Coordinate. ie: PlusMinus in 1D, circular
in 2D, spherical in 3D.

Symmetrical.radius 
attribute 
The uncertainty extent, constant in all dimensions and directions. 
Time 
objectType 
Provides a complete description of a measured Temporal instant. 
Time.coord 
attribute 
The measured time value. May be provided in any of the TimeStamp subtypes. 
Uncertainty 
dataType 
Abstract head of uncertainty types. These classes define the shape of the uncertainty, and are designed to be reusable in
different contexts. Uncertainties are designed to be associated with a Coordinate or other object which provides the 'center'
or reference location about which the uncertainty resides. In this model, we use them in the context of defining measurement
errors, but they are also compatible for use in defining resolutions which are to be modeled at a later date.
This initial version of teh model forms a fundamental basis which can then be expanded to include more complex and varied
use cases as they present themselves. The current model assumes Gaussian distributions with shpes defined at the 68% confidence
level.

Velocity 
objectType 
Provides a comple description of a measured Velocity instant. 
Velocity.coord 
attribute 
The measured Velocity value. The Point coordinate supports 1,2, and 3dimensional cases. Details of the coordinate system
(space and frame), are associated with the Point.
