org.jscience.geography.coordinates.crs

Class ReferenceEllipsoid

java.lang.Object

org.jscience.geography.coordinates.crs.ReferenceEllipsoid

public class ReferenceEllipsoid
extends java.lang.Object

The ReferenceEllipsoid class defines a geodetic reference ellipsoid used as a standard for geodetic measurements. The World Geodetic System 1984 (WGS84) ellipsoid is the current standard for most geographic and geodetic coordinate systems, including GPS. The WGS84 ellipsoid is provided as a static instance of this class.

The ellipsoid (actually an oblate spheroid) is uniquely specified by two parameters, the semimajor (or equatorial) radius and the ellipticity or flattening. In practice, the reciprocal of the flattening is specified.

The ellipsoid is an approximation of the shape of the earth. Although not exact, the ellipsoid is much more accurate than a spherical approximation and is still mathematically simple. The geoid is a still closer approximation of the shape of the earth (intended to represent the mean sea level), and is generally specified by it's deviation from the ellipsoid.

Different reference ellipsoids give more or less accurate results at different locations, so it was previously common for different nations to use ellipsoids that were more accurate for their areas. More recent efforts have provided ellipsoids with better overall global accuracy, such as the WGS84 ellipsiod, and these have now largely supplanted the others.

Version:

3.0, February 18, 2006

Author:

Paul D. Anderson

Field Summary

Fields

Modifier and Type	Field and Description
static ReferenceEllipsoid	GRS80 Geodetic Reference System 1980 ellipsoid.
static ReferenceEllipsoid	INTERNATIONAL1924 The International 1924 reference ellipsoid, one of the earliest "global" ellipsoids.
static ReferenceEllipsoid	WGS72 The World Geodetic System 1972 reference ellipsoid.
static ReferenceEllipsoid	WGS84 The World Geodetic System 1984 reference ellipsoid.

Constructor Summary

Constructors

Constructor and Description
ReferenceEllipsoid(double semimajorAxis, double inverseFlattening) Constructs an instance of a reference ellipsoid.

Method Summary

Modifier and Type	Method and Description
double	getEccentricity() Returns the (first) eccentricity of this reference ellipsoid.
double	getEccentricitySquared() Returns the square of the (first) eccentricity.
double	getFlattening() Returns the flattening or ellipticity of this reference ellipsoid.
double	getSecondEccentricitySquared() Returns the square of the second eccentricity of this reference ellipsoid.
Measurable<Length>	getSemimajorAxis() Returns the semimajor or equatorial radius of this reference ellipsoid.
Measurable<Length>	getsSemiminorAxis() Returns the semiminor or polar radius of this reference ellipsoid.
double	meridionalArc(double phi) Returns the meridional arc, the true meridional distance on the ellipsoid from the equator to the specified latitude, in meters.
Measurable<Length>	meridionalArc(Measurable<Angle> latitude) Returns the meridional arc, the true meridional distance on the ellipsoid from the equator to the specified latitude.
double	meridionalRadiusOfCurvature(double phi) Returns the radius of curvature in the meridian for this reference ellipsoid at the specified latitude.
Measurable<Length>	meridionalRadiusOfCurvature(Measurable<Angle> latitude) Returns the radius of curvature in the meridian for this reference ellipsoid at the specified latitude.
double	verticalRadiusOfCurvature(double phi) Returns the radius of curvature in the prime vertical for this reference ellipsoid at the specified latitude.
Measurable<Length>	verticalRadiusOfCurvature(Measurable<Angle> latitude) Returns the radius of curvature in the prime vertical for this reference ellipsoid at the specified latitude.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

WGS84

public static final ReferenceEllipsoid WGS84

The World Geodetic System 1984 reference ellipsoid.

GRS80

public static final ReferenceEllipsoid GRS80

Geodetic Reference System 1980 ellipsoid.

WGS72

public static final ReferenceEllipsoid WGS72

The World Geodetic System 1972 reference ellipsoid.

INTERNATIONAL1924

public static final ReferenceEllipsoid INTERNATIONAL1924

The International 1924 reference ellipsoid, one of the earliest "global" ellipsoids.

Constructor Detail

ReferenceEllipsoid

public ReferenceEllipsoid(double semimajorAxis,
                          double inverseFlattening)

Constructs an instance of a reference ellipsoid.

Parameters:

semimajorAxis - The semimajor or equatorial radius of this reference ellipsoid, in meters.

inverseFlattening - The reciprocal of the ellipticity or flattening of this reference ellipsoid (dimensionless).

Method Detail

getSemimajorAxis

public Measurable<Length> getSemimajorAxis()

Returns the semimajor or equatorial radius of this reference ellipsoid.

Returns:

The semimajor radius.

getsSemiminorAxis

public Measurable<Length> getsSemiminorAxis()

Returns the semiminor or polar radius of this reference ellipsoid.

Returns:

The semiminor radius.

getFlattening

public double getFlattening()

Returns the flattening or ellipticity of this reference ellipsoid.

Returns:

The flattening.

getEccentricity

public double getEccentricity()

Returns the (first) eccentricity of this reference ellipsoid.

Returns:

The eccentricity.

getEccentricitySquared

public double getEccentricitySquared()

Returns the square of the (first) eccentricity. This number is frequently used in ellipsoidal calculations.

Returns:

The square of the eccentricity.

getSecondEccentricitySquared

public double getSecondEccentricitySquared()

Returns the square of the second eccentricity of this reference ellipsoid. This number is frequently used in ellipsoidal calculations.

Returns:

The square of the second eccentricity.

verticalRadiusOfCurvature

public double verticalRadiusOfCurvature(double phi)

Returns the radius of curvature in the prime vertical for this reference ellipsoid at the specified latitude.

Parameters:

phi - The local latitude (radians).

Returns:

The radius of curvature in the prime vertical (meters).

verticalRadiusOfCurvature

public Measurable<Length> verticalRadiusOfCurvature(Measurable<Angle> latitude)

Returns the radius of curvature in the prime vertical for this reference ellipsoid at the specified latitude.

Parameters:

latitude - The local latitude.

Returns:

The radius of curvature in the prime vertical.

meridionalRadiusOfCurvature

public double meridionalRadiusOfCurvature(double phi)

Returns the radius of curvature in the meridian for this reference ellipsoid at the specified latitude.

Parameters:

phi - The local latitude (in radians).

Returns:

The radius of curvature in the meridian (in meters).

meridionalRadiusOfCurvature

public Measurable<Length> meridionalRadiusOfCurvature(Measurable<Angle> latitude)

Returns the radius of curvature in the meridian for this reference ellipsoid at the specified latitude.

Parameters:

latitude - The local latitude (in radians).

Returns:

The radius of curvature in the meridian (in meters).

meridionalArc

public double meridionalArc(double phi)

Returns the meridional arc, the true meridional distance on the ellipsoid from the equator to the specified latitude, in meters.

Parameters:

phi - The local latitude (in radians).

Returns:

The meridional arc (in meters).

meridionalArc

public Measurable<Length> meridionalArc(Measurable<Angle> latitude)

Returns the meridional arc, the true meridional distance on the ellipsoid from the equator to the specified latitude.

Parameters:

latitude - The local latitude.

Returns:

The meridional arc.