@UML(identifier="SC_CompoundCRS", specification=ISO_19111) public interface CompoundCRS extends CoordinateReferenceSystem
In general, a Compound CRS may contain any number of axes. The Compound CRS contains an ordered set of coordinate reference systems and the tuple order of a compound coordinate set shall follow that order, while the subsets of the tuple, described by each of the composing coordinate reference systems, follow the tuple order valid for their respective coordinate reference systems.
For spatial coordinates, a number of constraints exist for the construction of Compound CRSs. For example, the coordinate reference systems that are combined should not contain any duplicate or redundant axes. Valid combinations include:
Any coordinate reference system, or any of the above listed combinations of coordinate reference systems, can have a Temporal CRS added. More than one Temporal CRS may be added if these axes represent different time quantities. For example, the oil industry sometimes uses "4D seismic", by which is meant seismic data with the vertical axis expressed in milliseconds (signal travel time). A second time axis indicates how it changes with time (years), e.g. as a reservoir is gradually exhausted of its recoverable oil or gas).
|Modifier and Type||Method and Description|
The ordered list of coordinate reference systems.
@UML(identifier="componentReferenceSystem", obligation=MANDATORY, specification=ISO_19111) List<CoordinateReferenceSystem> getComponents()
Departure from OGC/ISO specification:
According ISO 19111, "A Compound CRS is a coordinate reference system that combines two or more coordinate reference systems, none of which can itself be compound". However this constraint greatly increases the cost of extracting metadata (especially the CRS identifier) of the three-dimensional part of a spatio-temporal CRS. Note also that in "Coordinate Transformation Services" (OGC document 01-009), a compound CRS was specified as a pair of arbitrary CRS ("head" and "tail") where each could be another compound CRS, allowing the creation of a tree. GeoAPI follows that more general strategy.
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