CylindricalCSPropertyType AffineCS Concrete coordinate systems .1 EllipsoidalCS

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12.4.4.20 AffineCSPropertyType

complexType name=AffineCSPropertyType sequence minOccurs=0 element ref=gml:AffineCS sequence attributeGroup ref=gml:AssociationAttributeGroup complexType gml:AffineCSPropertyType is a property type for association roles to an affine coordinate system, either referencing or containing the definition of that coordinate system.

12.5 Datums

12.5.1 Overview

The datums schema components can be divided into three logical parts, which define elements and types for XML encoding of the definitions of:  abstract datum;  geodetic datums, including ellipsoid and prime meridian;  multiple other concrete types of spatial or temporal datum. These schema components encode the Datum packages of the UML Models of ISO 19111:2007, Clause 10, and D.3.9 of this International Standard. NOTE The datums schema document includes the referenceSystems.xsd GML schema. This schema is identified by the following location-independent name using URN syntax: urn:x-ogc:specification:gml:schema-xsd:datums:3.2.1 12.5.2 Abstract datum 12.5.2.1 AbstractDatum element name=AbstractDatum type=gml:AbstractDatumType abstract=true substitutionGroup=gml:Definition complexType name=AbstractDatumType abstract=true complexContent extension base=gml:IdentifiedObjectType sequence element ref=gml:domainOfValidity minOccurs=0 element ref=gml:scope maxOccurs=unbounded element ref=gml:anchorDefinition minOccurs=0 element ref=gml:realizationEpoch minOccurs=0 sequence extension complexContent complexType A gml:AbstractDatum specifies the relationship of a coordinate system to the Earth, thus creating a coordinate reference system. A datum uses a parameter or set of parameters that determine the location of the origin of the coordinate reference system. Each datum subtype may be associated with only specific types of coordinate 118 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. system. This abstract complex type shall not be used, extended, or restricted, in a GML application schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document.

12.5.2.2 anchorDefinition

element name=anchorDefinition type=gml:CodeType gml:anchorDefinition is a description, possibly including coordinates, of the definition used to anchor the datum to the Earth, also kn own as the ―origin‖, especially for engineering and image datums. The codeSpace attribute may be used to reference a source of more detailed on this point or surface, or on a set of such descriptions.  For a geodetic datum, this point is also known as the fundamental point, which is traditionally the point where the relationship between geoid and ellipsoid is defined. In some cases, the fundamental point may consist of a number of points. In those cases, the parameters defining the geoidellipsoid relationship have been averaged for these points, and the averages adopted as the datum definition.  For an engineering datum, the anchor definition may be a physical point, or it may be a point with defined coordinates in another CRS.  For an image datum, the anchor definition is usually either the centre of the image or the corner of the image.  For a temporal datum, this attribute is not defined. Instead of the anchor definition, a temporal datum carries a separate time origin of type DateTime.

12.5.2.3 realizationEpoch

element name=realizationEpoch type=date gml:realizationEpoch is the time after which this datum definition is valid. See ISO 19111:2007, Table 33, for details.

12.5.2.4 DatumPropertyType

complexType name=DatumPropertyType sequence minOccurs=0 element ref=gml:AbstractDatum sequence attributeGroup ref=gml:AssociationAttributeGroup complexType gml:DatumPropertyType is a property type for association roles to a datum, either referencing or containing the definition of that datum. 12.5.3 Geodetic datum 12.5.3.1 GeodeticDatum element name=GeodeticDatum type=gml:GeodeticDatumType substitutionGroup=gml:AbstractDatum complexType name=GeodeticDatumType complexContent extension base=gml:AbstractDatumType sequence element ref=gml:primeMeridian