org.opengis.referencing.crs.package-info Maven / Gradle / Ivy

/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2011, Open Source Geospatial Foundation (OSGeo)
 *    (C) 2004-2005, Open Geospatial Consortium Inc.
 *
 *    All Rights Reserved. http://www.opengis.org/legal/
 */

/**
 * {@linkplain org.opengis.referencing.crs.CoordinateReferenceSystem Coordinate reference systems}
 * ({@linkplain org.opengis.referencing.cs.CoordinateSystem coordinate systems} with a {@linkplain
 * org.opengis.referencing.datum.Datum datum}). The following is adapted from OpenGIS® Spatial Referencing
 * by Coordinates (Topic 2) specification.
 *
 * A coordinate reference system consists of one coordinate system that is
 * related to the earth through one datum. The coordinate system is composed of a set of coordinate
 * axes with specified units of measure. This concept implies the mathematical rules that define how
 * coordinate values are calculated from distances, angles and other geometric elements and vice
 * versa.
 *
 * 
A datum specifies the relationship of a coordinate system to the earth, thus
 * ensuring that the abstract mathematical concept "coordinate system" can be applied to the
 * practical problem of describing positions of features on or near the earth's surface by means of
 * coordinates. The resulting combination of coordinate system and datum is a coordinate reference
 * system. Each datum subtype can be associated with only specific types of coordinate systems. The
 * datum implicitly (occasionally explicitly) contains the values chosen for the set parameters that
 * represent the degrees of freedom of the coordinate system. A datum therefore implies a choice
 * regarding the approximate origin and orientation of the coordinate system.
 *
 * 
For the purposes of this specification, a coordinate reference system shall
 * not change with time, with the exception of engineering coordinate reference systems defined on
 * moving platforms such as cars, ships, aircraft and spacecraft. The intention is to exclude the
 * option to describe the time variability of geodetic coordinate reference systems as a result of
 * e.g. tectonic motion. This variability is part of the subject matter of geophysical and geodetic
 * science. The model for spatial referencing by coordinates described in this specification is in
 * principle not suitable for such zero-order geodetic problems. Such time-variability of coordinate
 * reference systems shall be covered in the spatial referencing model described in this
 * specification by creating different coordinate reference systems, each with a different datum,
 * for (consecutive) epochs. The date of realisation of the datum shall then be included in its
 * definition. It is further recommended to include the date of realisation in the names of those
 * datums and coordinate reference systems.
 *
 * 
 
 *
 * 
Principal sub-types of coordinate reference system
 *
 * Geodetic survey practice usually divides coordinate reference systems into a
 * number of sub-types. The common classification criterion for sub-typing of coordinate reference
 * systems can be described as the way in which they deal with earth curvature. This has a direct
 * effect on the portion of the earth's surface that can be covered by that type of CRS with an
 * acceptable degree of error. Thus the following principal sub-types of coordinate reference system
 * are distinguished:
 *
 * 

 *
 * Geocentric: Type of coordinate reference system that deals with the
 * earth's curvature by taking the 3D spatial view, which obviates the need to model the earth's
 * curvature. The origin of a geocentric CRS is at the approximate centre of mass of the earth.
 *
 * 
Geographic: Type of coordinate reference system based on an ellipsoidal
 * approximation of the geoid. This provides an accurate representation of the geometry of
 * geographic features for a large portion of the earth's surface. Geographic coordinate reference
 * systems can be 2D or 3D. A 2D Geographic CRS is used when positions of features are described on
 * the surface of the reference ellipsoid; a 3D Geographic CRS is used when positions are described
 * on, above or below the reference ellipsoid.
 *
 * 
Projected: Type of coordinate reference system that is based on an
 * approximation of the shape of the earth's surface by a plane. The distortion that is inherent to
 * the approximation is carefully controlled and known. Distortion correction is commonly applied to
 * calculated bearings and distances to produce values that are a close match to actual field
 * values.
 *
 * 
Engineering: Type of coordinate reference system that is that is used
 * only in a contextually local sense. This sub-type is used to model two broad categories of local
 * coordinate reference systems:
 *
 * 

 *   earth-fixed systems, applied to engineering activities on or near the surface of the earth;
 *   
coordinates on moving platforms such as road vehicles, vessels, aircraft or spacecraft.
 * 
 *
 * Image: An Image CRS is an Engineering CRS applied to images. Image CRSs
 * are treated as a separate sub-type because a separate user community exists for images with its
 * own vocabulary. The definition of the associated Image Datum contains two data attributes not
 * relevant for other datums and coordinate reference systems.
 *
 * 
Vertical: Type of coordinate reference system used for the recording of
 * heights or depths. Vertical CRSs make use of the direction of gravity to define the concept of
 * height or depth, but its relationship with gravity may not be straightforward. By implication
 * ellipsoidal heights (h) cannot be captured in a vertical coordinate reference system. Ellipsoidal
 * heights cannot exist independently, but only as inseparable part of a 3D coordinate tuple defined
 * in a geographic 3D coordinate reference system.
 *
 * 
Temporal: Used for the recording of time in association with any of the
 * listed spatial coordinate reference systems only.
 *
 * 
 *
 *  
 *
 * 
Additional sub-types of coordinate reference system
 *
 * In addition to the principal sub-types, so called because they represent
 * concepts generally known in geodetic practice, two more sub-types have been defined to permit
 * modelling of certain relationships and constraints that exist between the principal sub-types.
 * These additional sub-types are Compound coordinate reference system
 * and Derived coordinate reference system.
 *
 * 

 *
 * Compound coordinate reference system

 * The traditional separation of horizontal and vertical position has resulted in coordinate
 * reference systems that are horizontal (2D) in nature and vertical (1D). It is established
 * practice to combine the horizontal coordinates of a point with a height or depth from a different
 * coordinate reference system. The coordinate reference system to which these 3D coordinates are
 * referenced combines the separate horizontal and vertical coordinate reference systems of the
 * horizontal and vertical coordinates. Such a coordinate system is called a compound coordinate
 * reference system (Compound CRS). It consists of an ordered sequence of the two or more single
 * coordinate reference systems.
 *
 * 
Derived coordinate reference system

 * Some coordinate reference systems are defined by applying a coordinate conversion to another
 * coordinate reference system. Such a coordinate reference system is called a Derived CRS and the
 * coordinate reference system it was derived from by applying the conversion is called the Source
 * or Base CRS. A coordinate conversion is an arithmetic operation with zero or more parameters that
 * have defined values. The Source CRS and Derived CRS have the same Datum. The best-known example
 * of a Derived CRS is a Projected CRS, which is always derived from a source Geographic CRS by
 * applying the coordinate conversion known as a map projection.
 *
 * 
In principle, all sub-types of coordinate reference system may take on the
 * role of either Source or Derived CRS with the exception of a Geocentric CRS and a Projected CRS.
 * The latter is modelled as an object class under its own name, rather than as a general Derived
 * CRS of type "projected". This has been done to honour common practice, which acknowledges
 * Projected CRSs as one of the best known types of coordinate reference systems.
 *
 * 
An example of a Derived CRS: one of which the unit of measure has been
 * modified with respect to an earlier defined Geographic CRS, which then takes the role of Source
 * CRS.
 *
 * 
 *
 * @version Abstract
 *     specification 2.0
 * @since GeoAPI 1.0
 */
package org.opengis.referencing.crs;