units.xsd v3.0 draft last updated 2002/04/22 GML 3.0 candidate schema. Copyright (c) 2002 OGC, All Rights Reserved. This schema encodes the Datums (CD_) package of the CRS UML model. A datum specifies the relationship of a coordinate system to the earth, thus crate a coordinate reference system. This specification uses a parameter or set of parameters that determine the location of the origin, the orientation, and the scale of a coordinate reference system. To be supplied. To be supplied. Association to a Datum, either referencing or containing the definition of that Datum. To be supplied. Association to an Engineering Datum, either referencing or containing the definition of that Datum. To be supplied. Association to an Image Datum, either referencing or containing the definition of that Datum. To be supplied. To be supplied. To be supplied. A textual description and/or a set of parameters identifying a particular reference level surface used as a zero-height surface, including its position and orientation with respect to the Earth for any of the height types recognized by this standard. Association to a Vertical Datum, either referencing or containing the definition of that Datum. To be supplied. To be supplied. To be supplied. Association to a Temporal Datum, either referencing or containing the definition of that Datum. The Geodetic Datum is an ellipsoid and a set of one or more reference points on the earth's surface. The physical location of these points is more or less consistent with their locations on their ellipsoidal coordinate system. A set of parameters defining the size and shape of the chosen reference ellipsoid and its position and orientation with respect to the Earth. To be supplied. To be supplied. Association to a Geodetic Datum, either referencing or containing the definition of that Datum. A prime meridian defines the origin from which longitude values are determined. To be supplied. Association to a Prime Meridian, either referencing or containing the definition of that Prime Meridian. An ellipsoid is a geometric figure that can used to describe the approximate shape of the earth. In mathematical terms, it is a surface formed by the rotation of an ellipse about an axis. To be supplied. Association to an Ellipsoid, either referencing or containing the definition of that Ellipsoid. An ellipsoid requires two defining parameters: semi-major axis and inverse flattening or semi-major axis and semi-minor axis. When the reference body is a sphere rather than an ellipsoid, only a single defining parameter is required, namely the radius of the sphere; in that case, the semi-major axis 'degenerates' into the radius of the sphere. To be supplied. To be supplied. To be supplied.