org.orekit.models.earth

Class ReferenceEllipsoid

java.lang.Object

org.orekit.bodies.Ellipsoid

org.orekit.bodies.OneAxisEllipsoid

org.orekit.models.earth.ReferenceEllipsoid

All Implemented Interfaces:

Serializable, BodyShape, EarthShape

public class ReferenceEllipsoid
extends OneAxisEllipsoid
implements EarthShape

A Reference Ellipsoid for use in geodesy. The ellipsoid defines an ellipsoidal potential called the normal potential, and its gradient, normal gravity.

These parameters are needed to define the normal potential:

• a, semi-major axis
• f, flattening
• GM, the gravitational parameter
• ω, the spin rate

References:

1. Martin Losch, Verena Seufer. How to Compute Geoid Undulations (Geoid Height Relative to a Given Reference Ellipsoid) from Spherical Harmonic Coefficients for Satellite Altimetry Applications. , 2003. mitgcm.org/~mlosch/geoidcookbook.pdf
2. Weikko A. Heiskanen, Helmut Moritz. Physical Geodesy. W. H. Freeman and Company, 1967. (especially sections 2.13 and equation 2-144)
3. Department of Defense World Geodetic System 1984. 2000. NIMA TR 8350.2 Third Edition, Amendment 1.

Author:

Evan Ward

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
ReferenceEllipsoid(double ae, double f, Frame bodyFrame, double GM, double spin) Creates a new geodetic Reference Ellipsoid from four defining parameters.

Method Summary

Modifier and Type	Method and Description
double	getC2n0(int n) Get the fully normalized coefficient C2n,0 for the normal gravity potential.
ReferenceEllipsoid	getEllipsoid() Get the underlying ellipsoid model that defines latitude and longitude.
double	getGM() Gets the gravitational parameter that is part of the definition of the reference ellipsoid.
static ReferenceEllipsoid	getGrs80(Frame bodyFrame) Get the GRS80 ellipsoid, attached to the given body frame.
double	getNormalGravity(double latitude) Gets the normal gravity, that is gravity just due to the reference ellipsoid's potential.
double	getPolarRadius() Get the radius of this ellipsoid at the poles.
double	getSpin() Gets the rotation of the ellipsoid about its axis.
static ReferenceEllipsoid	getWgs84(Frame bodyFrame) Get the WGS84 ellipsoid, attached to the given body frame.

Methods inherited from class org.orekit.bodies.OneAxisEllipsoid

getBodyFrame, getEquatorialRadius, getFlattening, getIntersectionPoint, projectToGround, projectToGround, setAngularThreshold, transform, transform, transform, transform

Methods inherited from class org.orekit.bodies.Ellipsoid

getA, getB, getC, getFrame, getPlaneSection, isInside, pointOnLimb

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.orekit.bodies.BodyShape

getBodyFrame, getIntersectionPoint, projectToGround, projectToGround, transform, transform

Constructor Detail

ReferenceEllipsoid

public ReferenceEllipsoid(double ae,
                          double f,
                          Frame bodyFrame,
                          double GM,
                          double spin)

Creates a new geodetic Reference Ellipsoid from four defining parameters.

Parameters:

ae - Equatorial radius, in m

f - flattening of the ellipsoid.

bodyFrame - the frame to attach to the ellipsoid. The origin is at the center of mass, the z axis is the minor axis.

GM - gravitational parameter, in m³/s²

spin - ω in rad/s

Method Detail

getGM

public double getGM()

Gets the gravitational parameter that is part of the definition of the reference ellipsoid.

Returns:

GM in m³/s²

getSpin

public double getSpin()

Gets the rotation of the ellipsoid about its axis.

Returns:

ω in rad/s

getPolarRadius

public double getPolarRadius()

Get the radius of this ellipsoid at the poles.

Returns:

the polar radius, in meters

See Also:

OneAxisEllipsoid.getEquatorialRadius()

getNormalGravity

public double getNormalGravity(double latitude)

Gets the normal gravity, that is gravity just due to the reference ellipsoid's potential. The normal gravity only depends on latitude because the ellipsoid is axis symmetric.

The normal gravity is a vector, having both magnitude and direction. This method only give the magnitude.

Parameters:

latitude - geodetic latitude, in radians. That is the angle between the local normal on the ellipsoid and the equatorial plane.

Returns:

the normal gravity, γ, at the given latitude in m/s². This is the acceleration felt by a mass at rest on the surface of the reference ellipsoid.

getC2n0

public double getC2n0(int n)

Get the fully normalized coefficient C_2n,0 for the normal gravity potential.

Parameters:

n - index in C_2n,0, n >= 1.

Returns:

normalized C_2n,0 of the ellipsoid

See Also:

"Department of Defense World Geodetic System 1984. 2000. NIMA TR 8350.2 Third Edition, Amendment 1.", "DMA TR 8350.2. 1984."

getEllipsoid

public ReferenceEllipsoid getEllipsoid()

Description copied from interface: EarthShape

Get the underlying ellipsoid model that defines latitude and longitude. If the height component of a GeodeticPoint is not needed, then using the ellipsoid will provide the quickest transformation.

Specified by:

getEllipsoid in interface EarthShape

Returns:

the reference ellipsoid. May be this, but never null.

getWgs84

public static ReferenceEllipsoid getWgs84(Frame bodyFrame)

Get the WGS84 ellipsoid, attached to the given body frame.

Parameters:

bodyFrame - the earth centered fixed frame

Returns:

a WGS84 reference ellipsoid

getGrs80

public static ReferenceEllipsoid getGrs80(Frame bodyFrame)

Get the GRS80 ellipsoid, attached to the given body frame.

Parameters:

bodyFrame - the earth centered fixed frame

Returns:

a GRS80 reference ellipsoid