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The Spatial Reference System Module
This module is based on the specifications: ISO 19111 – Geographic information – Spatial Referencing by Coordinates and OGC - Implementation Specification: Coordinate Transformation Services and at providing the mechanisms to represent a coordinate that describes a position on or near the Earth's surface and are referenced to a model of the Earth. Coordinates are referenced to a Coordinate Reference System (CRS). A Coordinate Reference System is a Coordinate System (CS) – an abstract mathematical concept without any relationship to a physical object – that is referenced through a Datum to the Earth or some other object such as a vessel.
The SRS module offers this concepts, as classes of the namespace te::srs
: including:SpatialReferenceSystem
, GeographicCoordinateSystem
,ProjectedCoordinateSystem
, GeographicCoordinateSystem
, Ellipsoid
and Datum
. Check the DOxygen documentation of this module, where these and other classes are documented in details.
In practice, users can describe an SRS in different ways:
- an arbitrary textual description (e.g. “UTM Zone 26S Datum WGS84”)
- an unique ID given by a responsible authority SRS Id and Authority responsible (e.g. EPSG 32726)
- a textual description as proposed by the PROJ.4 - Cartographic Projections Library (e.g.
+proj=utm +zone=26 +south +ellps=WGS84 +datum=WGS84 +units=m +no_defs
)
PROJ.4 descriptiosn it is not a OGC standard, PROJ.4 descriptions are used to represent SRS whenever PROJ.4 is used to perform transformations between two different SRS.
A Mananger is responsible for building SRS from textual representations identified by its types. The figure below shows the classes involved in this operation.