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Requirement http:www.opengis.netspecGML3.3reqtinvalid
Test purpose Verify that any XML node whose content model is specified using schema components in the
http:www.opengis.netgml3.3tin schema is well-
formed and valid. Test method
Validate the XML document using the XML schema document http:schemas.opengis.netgml3.3tin.xsd
. Pass if no errors reported. Fail otherwise.
Test type Basic
9 Linear Referencing
9.1 Target namespaces
Schema components specified in this Clause are in the following target namespaces, based on conformance class:
http:www.opengis.netgml3.3lr - Basic linear referencing functionality
http:www.opengis.netgml3.3lrtr - Towards referent extension; dependent upon gmllr
http:www.opengis.netgml3.3lro - Offset extension; dependent upon gmllr
http:www.opengis.netgml3.3lrov - Offset vector extension; dependent upon gmllr and gmllro
9.2 Introduction
GML 3.2 and other OGC specifications so far mainly support 2-D and 3-D spatial locations. An alternative location scheme is to use linearly referenced locations, where a location is specified as being at a certain
distance along and perhaps offset from a linear element. The linear element might be a feature which exhibits linear behaviour i.e., it is linearly measurable, a curve type of geometry, or a directed edge type of
topology.
A significant amount of historical data is currently linearly referenced, especially in the transportation, piping, petroleum and mineral exploration industries. There are advantages of using this scheme over or in addition
to spatial referencing.
Just as spatial data may utilize a variety of spatial coordinate reference systems, linearly referenced locations use a wide variety of Linear Referencing Methods LRM. A well documented theoretical basis has
been developed to support many of the more common LRMs in practice internationally today ISODIS 19148 and OGC Abstract Specification Topic 19.
9.3 Basic Linear Referencing
9.3.1 Target namespace
All schema components specified in this subclause are in the target namespace: http:www.opengis.netgml3.3lr
30 Copyright © 2012 Open Geospatial Consortium
9.3.2 Introduction
Basic Linear Referencing includes the specification of linearly referenced locations. These are described by a position expression which consists of the linear element being measured, the method of measurement and a
measure value specified with a distance expression.
9.3.3 PositionExpression
