org.orekit.bodies
Class OneAxisEllipsoid

java.lang.Object
  org.orekit.bodies.OneAxisEllipsoid

All Implemented Interfaces:

java.io.Serializable, BodyShape

public class OneAxisEllipsoid
extends java.lang.Object
implements BodyShape

Modeling of a one-axis ellipsoid.

One-axis ellipsoids is a good approximate model for most planet-size and larger natural bodies. It is the equilibrium shape reached by a fluid body under its own gravity field when it rotates. The symmetry axis is the rotation or polar axis.

This class is a simple adaptation of the Ellipsoid example class implementing the algorithms described in the paper Quick computation of the distance between a point and an ellipse.

Version:

$Revision:1665 $ $Date:2008-06-11 12:12:59 +0200 (mer., 11 juin 2008) $

Author:

Luc Maisonobe

See Also:

Serialized Form

Constructor Summary

OneAxisEllipsoid(double ae, double f, Frame bodyFrame)
Simple constructor.

Method Summary

Frame	getBodyFrame() Get the body frame related to body shape.
double	getEquatorialRadius() Get the equatorial radius of the body.
GeodeticPoint	getIntersectionPoint(Line line, org.apache.commons.math.geometry.Vector3D close, Frame frame, AbsoluteDate date) Get the intersection point of a line with the surface of the body.
void	setAngularThreshold(double angularThreshold) Set the angular convergence threshold.
void	setCloseApproachThreshold(double closeApproachThreshold) Set the close approach threshold.
org.apache.commons.math.geometry.Vector3D	transform(GeodeticPoint point) Transform a surface-relative point to a cartesian point.
GeodeticPoint	transform(org.apache.commons.math.geometry.Vector3D point, Frame frame, AbsoluteDate date) Transform a cartesian point to a surface-relative point.

Methods inherited from class java.lang.Object

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

Constructor Detail

OneAxisEllipsoid

public OneAxisEllipsoid(double ae,
                        double f,
                        Frame bodyFrame)

Simple constructor.

The following table provides conventional parameters for global Earth models:

model	ae (m)	f
GRS 80	6378137.0	1.0 / 298.257222101
WGS84	6378137.0	1.0 / 298.257223563

Parameters:

ae - equatorial radius

f - the flattening (f = (a-b)/a)

bodyFrame - body frame related to body shape

See Also:

FramesFactory.getITRF2005()

Method Detail

setCloseApproachThreshold

public void setCloseApproachThreshold(double closeApproachThreshold)

Set the close approach threshold.

The close approach threshold is a ratio used to identify special cases in the transform(Vector3D, Frame, AbsoluteDate) method.

Let d = (x²+y²+z²)^½ be the distance between the point and the ellipsoid center.

• all points such that d<ε a_e where a_e is the equatorial radius of the ellipsoid are considered at the center
• all points closer to the surface of the ellipsoid than ε d are considered on the surface

If this method is not called, the default value is set to 10^-10.

Parameters:

closeApproachThreshold - close approach threshold (no unit)

setAngularThreshold

public void setAngularThreshold(double angularThreshold)

Set the angular convergence threshold.

The angular threshold is the convergence threshold used to stop the iterations in the transform(Vector3D, Frame, AbsoluteDate) method. It applies directly to the latitude. When convergence is reached, the real latitude is guaranteed to be between φ - δ&phi/2 and φ + δ&phi/2 where φ is the computed latitude and δ&phi is the angular threshold set by this method.

If this method is not called, the default value is set to 10^-14.

Parameters:

angularThreshold - angular convergence threshold (rad)

getEquatorialRadius

public double getEquatorialRadius()

Get the equatorial radius of the body.

Returns:

equatorial radius of the body (m)

getBodyFrame

public Frame getBodyFrame()

Get the body frame related to body shape.

Specified by:

getBodyFrame in interface BodyShape

Returns:

body frame related to body shape

getIntersectionPoint

public GeodeticPoint getIntersectionPoint(Line line,
                                          org.apache.commons.math.geometry.Vector3D close,
                                          Frame frame,
                                          AbsoluteDate date)
                                   throws OrekitException

Get the intersection point of a line with the surface of the body.

A line may have several intersection points with a closed surface (we consider the one point case as a degenerated two points case). The close parameter is used to select which of these points should be returned. The selected point is the one that is closest to the close point.

Specified by:

getIntersectionPoint in interface BodyShape

Parameters:

line - test line (may intersect the body or not)

close - point used for intersections selection

frame - frame in which line is expressed

date - date of the line in given frame

Returns:

intersection point at altitude zero or null if the line does not intersect the surface

Throws:

OrekitException - if line cannot be converted to body frame

See Also:

Line.getAbscissa(Vector3D), Line.pointAt(double)

transform

public org.apache.commons.math.geometry.Vector3D transform(GeodeticPoint point)

Transform a surface-relative point to a cartesian point.

Specified by:

transform in interface BodyShape

Parameters:

point - surface-relative point

Returns:

point at the same location but as a cartesian point

transform

public GeodeticPoint transform(org.apache.commons.math.geometry.Vector3D point,
                               Frame frame,
                               AbsoluteDate date)
                        throws OrekitException

Transform a cartesian point to a surface-relative point.

Specified by:

transform in interface BodyShape

Parameters:

point - cartesian point

frame - frame in which cartesian point is expressed

date - date of the point in given frame

Returns:

point at the same location but as a surface-relative point, expressed in body frame

Throws:

OrekitException - if point cannot be converted to body frame