units.xsd v3.0 draft last updated 2002/04/21 GML 3.0 candidate schema. Copyright (c) 2002 OGC, All Rights Reserved. This schema encodes the units of Coordinate Systems (CS_) package of the CRS UML Model. A coordinate system (CS) is the set of coordinate system axes that spans a given coordinate space. A CS is derived from a set of (mathematical) rules for specifying how coordinates in a given space are to be assigned to points. Association to a Coordinate System, either referencing or containing the definition of that Coordinate System. Types of coordinate systems. A 1-, 2-, or 3-dimensional coordinate system. Gives the position of points relative to orthogonal straight axes in the 2- and 3-dimensional cases. In the 1-dimensional case, it contains a single straight coordinate axis. In the multi-dimensional case, all axes shall have the same length unit of measure. Association to a Cartesian Coordinate System, either referencing or containing the definition of that Coordinate System. A two-dimensional coordinate system in which position is specified by distance to the origin and the angle between the line from the origin to a point and a reference direction. Association to a Polar Coordinate System, either referencing or containing the definition of that Coordinate System. A three-dimensional coordinate system with one distance measured from the origin and two angular coordinates. Not to be confused with an ellipsoidal coordinate system based on an ellipsoid 'degenerated' into a sphere Association to a Spherical Coordinate System, either referencing or containing the definition of that Coordinate System. A three-dimensional coordinate system consisting of a polar coordinate system extended by a straight coordinate axis perpendicular to the plane spanned by the polar coordinate system. Association to a Cylindrical Coordinate System, either referencing or containing the definition of that Coordinate System. A coordinate system containing one or more coordinate system axes that may have any shape that has no intersections with itself. This/these axes may be supplemented by one or two straight axes to complete a 2 or 3 dimensional coordinate system. The non-straight axes are typically incrementally straight or curved. Association to a Multi-Linear Coordinate System, either referencing or containing the definition of that Coordinate System. A coordinate system with straight lines that are not necessarily orthogonal. Association to an Oblique Cartesian Coordinate System, either referencing or containing the definition of that Coordinate System. A one-dimensional coordinate system used to record the heights (or depths) of points dependent on the Earth's gravity field. An exact definition is deliberately not provided as the complexities of the subject fall outside the scope of this specification. Association to a Gravity Related Coordinate System, either referencing or containing the definition of that Coordinate System. A two- or three-dimensional coordinate system in which position is specified by geodetic latitude, geodetic longitude, and (in the three-dimensional case) ellipsoidal height. Association to an Ellipsoidal Coordinate System, either referencing or containing the definition of that Coordinate System. A coordinate system that is one-dimensional and consists of the points that lie on the single axis described. The associated ordinate is the distance from the specified origin to the point along the axis. Example: usage of the line feature representing a road to describe points on or along that road. Association to a Linear Coordinate System, either referencing or containing the definition of that Coordinate System. A 1-dimensional coordinate system containing a single time axis, and used to describe the temporal position of a point in the specified time units from a specified time origin. Association to a Temporal Coordinate System, either referencing or containing the definition of that Coordinate System. Defintion of a coordinate system axis. Association to a Coordinate System Axis, either referencing or containing the definition of that Coordinate System Axis.