coordinateSystems.xsd
See ISO/DIS 19136 13.4.
The coordinate systems schema components can be divded into three logical parts, which define elements and types for XML encoding of the definitions of:
- Coordinate system axes
- Abstract coordinate system
- Multiple concrete types of spatial-temporal coordinate systems
These schema components encode the Coordinate System packages of the UML Models of ISO 19111 Clause 9 and ISO/DIS 19136 D.3.10.
gml:CoordinateSystemAxis is a definition of a coordinate system axis.
gml:axisAbbrev is the abbreviation used for this coordinate system axis; this abbreviation is also used to identify the coordinates in the coordinate tuple. The codeSpace attribute may reference a source of more information on a set of standardized abbreviations, or on this abbreviation.
gml:axisDirection is the direction of this coordinate system axis (or in the case of Cartesian projected coordinates, the direction of this coordinate system axis at the origin).
Within any set of coordinate system axes, only one of each pair of terms may be used. For earth-fixed CRSs, this direction is often approximate and intended to provide a human interpretable meaning to the axis. When a geodetic datum is used, the precise directions of the axes may therefore vary slightly from this approximate direction.
The codeSpace attribute shall reference a source of information specifying the values and meanings of all the allowed string values for this property.
The gml:minimumValue and gml:maximumValue properties allow the specification of minimum and maximum value normally allowed for this axis, in the unit of measure for the axis. For a continuous angular axis such as longitude, the values wrap-around at this value. Also, values beyond this minimum/maximum can be used for specified purposes, such as in a bounding box. A value of minus infinity shall be allowed for the gml:minimumValue element, a value of plus infiniy for the gml:maximumValue element. If these elements are omitted, the value is unspecified.
The gml:minimumValue and gml:maximumValue properties allow the specification of minimum and maximum value normally allowed for this axis, in the unit of measure for the axis. For a continuous angular axis such as longitude, the values wrap-around at this value. Also, values beyond this minimum/maximum can be used for specified purposes, such as in a bounding box. A value of minus infinity shall be allowed for the gml:minimumValue element, a value of plus infiniy for the gml:maximumValue element. If these elements are omitted, the value is unspecified.
gml:rangeMeaning describes the meaning of axis value range specified by gml:minimumValue and gml:maximumValue. This element shall be omitted when both gml:minimumValue and gml:maximumValue are omitted. This element should be included when gml:minimumValue and/or gml:maximumValue are included. If this element is omitted when the gml:minimumValue and/or gml:maximumValue are included, the meaning is unspecified. The codeSpace attribute shall reference a source of information specifying the values and meanings of all the allowed string values for this property.
The uom attribute provides an identifier of the unit of measure used for this coordinate system axis. The value of this coordinate in a coordinate tuple shall be recorded using this unit of measure, whenever those coordinates use a coordinate reference system that uses a coordinate system that uses this axis.
gml:CoordinateSystemAxisPropertyType is a property type for association roles to a coordinate system axis, either referencing or containing the definition of that axis.
gml:AbstractCoordinateSystem is a coordinate system (CS) is the non-repeating sequence 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. The coordinate values in a coordinate tuple shall be recorded in the order in which the coordinate system axes associations are recorded. This abstract complex type shall not be used, extended, or restricted, in an Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.
The gml:axis property is an association role (ordered sequence) to the coordinate system axes included in this coordinate system. The coordinate values in a coordinate tuple shall be recorded in the order in which the coordinate system axes associations are recorded, whenever those coordinates use a coordinate reference system that uses this coordinate system. The gml:AggregationAttributeGroup should be used to specify that the axis objects are ordered.
gml:CoordinateSystemPropertyType is a property type for association roles to a coordinate system, either referencing or containing the definition of that coordinate system.
gml:EllipsoidalCS is 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. An EllipsoidalCS shall have two or three gml:axis property elements; the number of associations shall equal the dimension of the CS.
gml:EllipsoidalCSPropertyType is a property type for association roles to an ellipsoidal coordinate system, either referencing or containing the definition of that coordinate system.
gml:CartesianCS is a 1-, 2-, or 3-dimensional coordinate system. In the 1-dimensional case, it contains a single straight coordinate axis. In the 2- and 3-dimensional cases gives the position of points relative to orthogonal straight axes. In the multi-dimensional case, all axes shall have the same length unit of measure. A CartesianCS shall have one, two, or three gml:axis property elements.
gml:CartesianCSPropertyType is a property type for association roles to a Cartesian coordinate system, either referencing or containing the definition of that coordinate system.
gml:VerticalCS is a one-dimensional coordinate system used to record the heights or depths of points. Such a coordinate system is usually dependent on the Earth's gravity field, perhaps loosely as when atmospheric pressure is the basis for the vertical coordinate system axis. A VerticalCS shall have one gml:axis property element.
gml:VerticalCSPropertyType is a property type for association roles to a vertical coordinate system, either referencing or containing the definition of that coordinate system.