## Package org.opengis.referencing

Reference systems.

See:
Description

Interface Summary
AuthorityFactory: Base interface for all authority factories.
Factory: Base interface for all factories.
IdentifiedObject: Supplementary identification and remarks information for a CRS or CRS-related object.
ObjectFactory: Base interface for all factories of identified objects.
ReferenceIdentifier: Identifier used for reference systems.
ReferenceSystem: Description of a spatial and temporal reference system used by a dataset.
SpatialReferenceSystemUsingGeographicIdentifier: Spatial reference system using geographic identifier, a reference to a feature with a known spatial location.

Exception Summary
FactoryException: Thrown when a factory can't create an instance of the requested object.
NoSuchAuthorityCodeException: Thrown when an authority factory can't find the requested authority code.
NoSuchIdentifierException: Thrown when a math transform as been requested with an unknow operation method identifier.

## Package org.opengis.referencing Description

Reference systems. The following is adapted from OpenGIS® Spatial Referencing by Coordinates (Topic 2) specification.

A reference system contains the metadata required to interpret spatial location information unambiguously. The description of an object's attributes can be done explicitly, by providing all defining parameters, or by identifier, a reference to a recognised source that contains a full description of the object.

The `IdentifiedObject` interface contains attributes common to several objects used in spatial referencing by coordinates. For example, a datum name might be "North American Datum of 1983". This may have alternative names or aliases, for example the abbreviation "NAD83". Object primary names have a data type `Identifier` whilst aliases have a data type `GenericName`.

Another attribute is identifiers. This is a unique code used to reference an object in a given place. For example, an external geodetic register might give the NAD83 datum a unique code of "6269". Identifiers have a data type of `Identifier`. In addition to the use of an identifier as a reference to a definition in a remote register, it may also be included in an object definition to allow remote users to refer to the object.

Most interfaced objects are immutable. This means that implementations promise not to change an object's internal state once they have handed out an interface pointer. Since most interfaced objects are specified to be immutable, there do not need to be any constraints on operation sequencing. This means that these interfaces can be used in parallel computing environments (e.g. internet servers).

## Well-Known Text format

Many entities in this specification can be printed in a well-known text format. This allows objects to be stored in databases (persistence), and transmitted between interoperating computer programs. The definition for WKT is shown using Extended Backus Naur Form (EBNF).

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