TemporalDatumPropertyType Other concrete datums .1 EngineeringDatum

124 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved.

12.6 Coordinate operations

12.6.1 Overview

The spatial or temporal coordinate operations schema components can be divided into five logical parts, which define elements and types for XML encoding of the definitions of:  Multiple abstract coordinate operations  Multiple concrete types of coordinate operation, including Transformations and Conversions  Abstract and concrete parameter values and groups  Operation methods  Abstract and concrete operation parameters and groups These schema components encode the Coordinate Operation package of the UML Model for ISO 19111:2007, Clause 11. NOTE The coordinateOperations schema includes the coordinateOperations.xsd GML schema document. This schema document is identified by the following location-independent name using URN syntax: urn:x-ogc:specification:gml:schema-xsd:coordinateOperations:3.2.1 12.6.2 Abstract coordinate operations 12.6.2.1 AbstractCoordinateOperation element name=AbstractCoordinateOperation type=gml:AbstractCoordinateOperationType abstract=true substitutionGroup=gml:Definition complexType name=AbstractCoordinateOperationType abstract=true complexContent extension base=gml:IdentifiedObjectType sequence element ref=gml:domainOfValidity minOccurs=0 element ref=gml:scope maxOccurs=unbounded element ref=gml:operationVersion minOccurs=0 element ref=gml:coordinateOperationAccuracy minOccurs=0 maxOccurs=unbounded element ref=gml:sourceCRS minOccurs=0 element ref=gml:targetCRS minOccurs=0 sequence extension complexContent complexType gml:AbstractCoordinateOperation is a mathematical operation on coordinates that transforms or converts coordinates to another coordinate reference system. Many but not all coordinate operations from CRS A to CRS B also uniquely define the inverse operation from CRS B to CRS A. In some cases, the operation method algorithm for the inverse operation is the same as for the forward algorithm, but the signs of some operation parameter values shall be reversed. In other cases, different algorithms are required for the forward and inverse operations, but the same operation parameter values are used. If some entirely different parameter values are needed, a different coordinate operation shall be defined. Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 125 The optional gml:coordinateOperationAccuracy property elements provide estimates of the impact of this coordinate operation on point position accuracy.

12.6.2.2 operationVersion

element name=operationVersion type=string gml:operationVersion is the version of the coordinate transformation i.e., instantiation due to the stochastic nature of the parameters. Mandatory when describing a transformation, and should not be supplied for a conversion.

12.6.2.3 coordinateOperationAccuracy

element name=coordinateOperationAccuracy complexType sequence minOccurs=0 element ref=gmd:AbstractDQ_PositionalAccuracy sequence attributeGroup ref=gml:AssociationAttributeGroup complexType element gml:coordinateOperationAccuracy is an association role to a DQ_PositionalAccuracy object as encoded in ISOTS 19139, either referencing or containing the definition of that positional accuracy. That object contains an estimate of the impact of this coordinate operation on point positional accuracy. That is, it gives position error estimates for the target coordinates of this coordinate operation, assuming no errors in the source coordinates.

12.6.2.4 sourceCRS

element name=sourceCRS type=gml:CRSPropertyType gml:sourceCRS is an association role to the source CRS coordinate reference system of this coordinate operation.

12.6.2.5 targetCRS

element name=targetCRS type=gml:CRSPropertyType gml:targetCRS is an association role to the target CRS coordinate reference system of this coordinate operation.

12.6.2.6 CoordinateOperationPropertyType

complexType name=CoordinateOperationPropertyType sequence minOccurs=0 element ref=gml:AbstractCoordinateOperation sequence attributeGroup ref=gml:AssociationAttributeGroup complexType gml:CoordinateOperationPropertyType is a property type for association roles to a coordinate operation, either referencing or containing the definition of that coordinate operation.