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Coordinate Reference Systems (CRS)Contents |
Background
A coordinate reference system is a specification of the physical shape the earth and its point of origin (the datum) and a selected coordinate system that defines points on the surface. Together these two parts are necessary and sufficient to define a framework for locating unambiguously and precisely every point on land or sea. The subject is covered by ISO 19115:2007 (reference below), and by the excellent background paper from the Open Geospatial Consortium (reference below) if you do not have access to ISO publications
Datums
The concept of datum, and the available datums are described in the excellent reference paper by Dana (see below). Each datum is based on a specific mathematical ellipsoid; some datums have their own unique ellipsoid, and some ellipsoids have been used by multiple datums. The current most widely used datum is the World Geodetic System 1984 (WGS84), also described in a reference below, based on its own WGS84 ellipsoid. There are also continental-scale datums (e.g. European Datum 1950, based on the International 1924 ellipsoid) and national-scale datums (e.g. North American Datum 1983 [NAD83], based on the GRS 80 ellipsoid)
Coordinate Systems
These are discussed in the article Coordinate Systems for the Earth Surface.
Coordinate Reference Systems (CRS)
A CRS is uniquely defined by a combination of any datum with any coordinate system. If no coordinate system is specified, the common geodetic or geographic coordinate system (GRS) is to be assumed.
Errors Associated with Incorrect Datum
Location errors up to 1 km can arise from the mistaken use of the wrong datum, according to Dana (see reference below), absent any other gross errors. Many other sources mention errors on the order of 100 m as typical.
Additional Resources
- A nearly official Coordinate Reference System Registry - Oil industry compilation of hundreds of CRSs worldwide
- Wikipedia: WGS84 - World Geodetic System 1984
- Geodetic Datum Overview - Excellent notes and resource links by Peter Dana, University of Texas
- Coordinate Systems Overview - Excellent notes and resource links by Peter Dana, University of Texas
- Wikipedia: Datum (geodesy)
- OGC Abstract Specifications: Topic 2 - Spatial Referencing by Coordinates - 2004 background document on which ISO 19111 is partly based; public domain and available
- ISO 19111:2007 Geographic information -- Spatial referencing by coordinates
- Wikipedia: Latitude
- Wikipedia: Longitude
- Wikipedia: Universal Transverse Mercator coordinate system
Subsections of this Article
No subsections available
Information about this article
Short title: Coordinate Reference Systems (CRS)
Description: none
Expertise level: beginner
Author: Murray.Brown
Approval status: approved
Approved by: Murray.Brown
Last change: 2008-10-3
Subsection of: Coordinate Systems for the Earth Surface
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