jat.spacetime
Class EarthRef

java.lang.Object
  jat.spacetime.EarthRef

All Implemented Interfaces:

BodyRef

public class EarthRef
extends java.lang.Object
implements BodyRef

The EarthRef Class provides methods of converting between various types of Earth reference systems. Reference: Satellite Orbits by Montenbruck and Gill. This is basically their C++ code converted to Java. The interface to this class is an input Terrestrial time in MJD format, which is available from either the CalDate or GPSTimeFormat classes.

Version:

1.0

Author:

Dave Gaylor

Field Summary

static double	f_Earth Flattening factor of earth from WGS-84
static double	GM_Earth Earth gravity constant in m^3/s^2 from JGM3
static double	omega_e Earth's rotation rate in rad/s.
static double	R_Earth Equatorial radius of earth in m from WGS-84
boolean	use_moon
boolean	use_sun

Constructor Summary

EarthRef(double MJD_UT1, double MJD_TT)
Construct an EarthRef object using UTC Time in Modified Julian Date format.

EarthRef(double MJD_UT1, double MJD_TT, boolean use_moon, boolean use_sun)
Construct an EarthRef object using UTC Time in Modified Julian Date format.

EarthRef(Time t0)
Construct an EarthRef object using UTC Time in Modified Julian Date format.

Method Summary

Matrix	body_to_inertial(Time t) Returns the (precalculated) eci2ecef transformation.
Matrix	ECI2ECEF() Returns the (precalculated) ECI to ECEF (ICRF to ITRF) Transformation Matrix.
Matrix	eci2ecef(double MJD_UT1, double MJD_TT) ECI to ECEF Transformation
Matrix	eci2ecef(Time t) ECI to ECEF Transformation
RotationMatrix	EclMatrix(double MJD_TT) Transformation of equatorial to ecliptical coordinates.
double	EqnEquinox(double MJD_TT) Computation of the equation of the equinoxes.
double	GAST(double MJD_UT1, double MJD_TT) Greenwich Apparent Sidereal Time.
double	get_grav_const() Returns the Earth's gravitational constant.
VectorN	get_JPL_Moon_Vector() Return the (precalculated) JPL Moon Vector
VectorN	get_JPL_Sun_Vector() Return the (precalculated) JPL Sun Vector
double	get_mean_radius() Returns the mean Earth Radius.
double	get_omega_e(double mjd_ut1) Return the dynamic rotation rate of the Earth at the given time.
double	get_omega_e(Time t) Return the dynamic rotation rate of the Earth at the given Time.
double	get_spin_rate(Time t) Returnts the dynamic Earth rotation rate.
RotationMatrix	GHAMatrix(double MJD_UT1, double MJD_TT) Transformation from true equator and equinox to Earth equator and Greenwich meridian system.
double	GMST(double MJD_UT1) Greenwich Mean Sidereal Time.
Matrix	inertial_to_body(Time t) Returns the transformation between inertial and body coordinates.
void	initializeMoonEphem(double MJD_TT) Initialize the JPL DE405 ephemerides and initialize the Moon vector.
void	initializeSunEphem(double MJD_TT) Initialize the JPL DE405 ephemerides and initialize the Sun vector.
static void	main(java.lang.String[] args) Test method.
double	MeanObliquity(double MJD_TT) Computes the mean obliquity of the ecliptic.
VectorN	moonVector(double MJD_TT) Computes the Moon's geocentric position using a low precision analytical series.
void	NutAngles(double MJD_TT) Computes Nutation in longitude and obliquity using the IAU 1980 nutation theory.
Matrix	NutMatrix(double MJD_TT) Transformation from mean to true equator and equinox.
Matrix	NutMatrixSimple(double MJD_TT) Transformation from mean to true equator and equinox (low precision).
Matrix	PoleMatrix() Transformation from pseudo Earth-fixed to Earth-fixed coordinates for a given date.
Matrix	PrecMatrix(double MJD_TT) Precession transformation of equatorial coordinates.
void	set_use_moon(boolean b) Set the flag whether to calculate the Moon's position.
void	set_use_sun(boolean b) Set the flag whether to calculate the Sun's position.
void	setIERS(double x, double y) Set the IERS (Earth Rotation) Data
VectorN	sunVector(double MJD_TT) Computes the Sun's geocentric position using a low precision analytical series.
Matrix	TOD() Returns the (precalculated) J2000 to True of Date (ICRF to TOD) Transformation Matrix.
Matrix	trueOfDate(double MJD_TT) J2000 to TOD Transformation
Matrix	trueOfDate(Time t) Returns the trueOfDate trasformation.
void	update(double MJD_UT1, double MJD_TT) Updates the Earth model.

Methods inherited from class java.lang.Object

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

Field Detail

use_moon

public boolean use_moon

use_sun

public boolean use_sun

omega_e

public static final double omega_e

Earth's rotation rate in rad/s.

See Also:

Constant Field Values

R_Earth

public static final double R_Earth

Equatorial radius of earth in m from WGS-84

See Also:

Constant Field Values

f_Earth

public static final double f_Earth

Flattening factor of earth from WGS-84

See Also:

Constant Field Values

GM_Earth

public static final double GM_Earth

Earth gravity constant in m^3/s^2 from JGM3

See Also:

Constant Field Values

Constructor Detail

EarthRef

public EarthRef(Time t0)

Construct an EarthRef object using UTC Time in Modified Julian Date format.

Parameters:

mjd_UTC - UTC time in MJD format.

EarthRef

public EarthRef(double MJD_UT1,
                double MJD_TT)

Construct an EarthRef object using UTC Time in Modified Julian Date format.

Parameters:

mjd_UTC - UTC time in MJD format.

EarthRef

public EarthRef(double MJD_UT1,
                double MJD_TT,
                boolean use_moon,
                boolean use_sun)

Construct an EarthRef object using UTC Time in Modified Julian Date format.

Parameters:

mjd_UTC - UTC time in MJD format.

Method Detail

setIERS

public void setIERS(double x,
                    double y)

Set the IERS (Earth Rotation) Data

Parameters:

x - x_pole coordinate (rad)

y - y_pole coordinate (rad)

initializeMoonEphem

public void initializeMoonEphem(double MJD_TT)

Initialize the JPL DE405 ephemerides and initialize the Moon vector.

initializeSunEphem

public void initializeSunEphem(double MJD_TT)

Initialize the JPL DE405 ephemerides and initialize the Sun vector.

ECI2ECEF

public Matrix ECI2ECEF()

Returns the (precalculated) ECI to ECEF (ICRF to ITRF) Transformation Matrix.

Returns:

ECI to ECEF Transformation Matrix.

TOD

public Matrix TOD()

Returns the (precalculated) J2000 to True of Date (ICRF to TOD) Transformation Matrix.

Returns:

J2000 to TOD Transformation Matrix.

MeanObliquity

public double MeanObliquity(double MJD_TT)

Computes the mean obliquity of the ecliptic. Uses Mjd_TT (Terrestrial Time).

Returns:

Mean obliquity of the ecliptic

EclMatrix

public RotationMatrix EclMatrix(double MJD_TT)

Transformation of equatorial to ecliptical coordinates. Uses Mjd_TT (Terrestrial Time).

Returns:

Transformation matrix

PrecMatrix

public Matrix PrecMatrix(double MJD_TT)

Precession transformation of equatorial coordinates. Uses Mjd_TT (Terrestrial Time).

Returns:

Precession transformation matrix

NutAngles

public void NutAngles(double MJD_TT)

Computes Nutation in longitude and obliquity using the IAU 1980 nutation theory. Uses Mjd_TT (Terrestrial Time).

NutMatrix

public Matrix NutMatrix(double MJD_TT)

Transformation from mean to true equator and equinox. Uses Mjd_TT (Terrestrial Time).

Returns:

Nutation matrix

NutMatrixSimple

public Matrix NutMatrixSimple(double MJD_TT)

Transformation from mean to true equator and equinox (low precision). Uses Mjd_TT (Terrestrial Time).

Returns:

Nutation matrix

EqnEquinox

public double EqnEquinox(double MJD_TT)

Computation of the equation of the equinoxes. Uses Mjd_TT (Terrestrial Time). Notes: The equation of the equinoxes dpsi*Math.cos(eps) is the right ascension of the mean equinox referred to the true equator and equinox and is equal to the difference between apparent and mean sidereal time.

Returns:

Equation of the equinoxes

GMST

public double GMST(double MJD_UT1)

Greenwich Mean Sidereal Time. Uses Mjd_UT1.

Returns:

GMST in [rad]

GAST

public double GAST(double MJD_UT1,
                   double MJD_TT)

Greenwich Apparent Sidereal Time.

Returns:

GAST in [rad]

GHAMatrix

public RotationMatrix GHAMatrix(double MJD_UT1,
                                double MJD_TT)

Transformation from true equator and equinox to Earth equator and Greenwich meridian system.

Returns:

Greenwich Hour Angle matrix

PoleMatrix

public Matrix PoleMatrix()

Transformation from pseudo Earth-fixed to Earth-fixed coordinates for a given date. Uses Mjd_UTC if poles are a function of UTC.

Returns:

Pole matrix

trueOfDate

public Matrix trueOfDate(double MJD_TT)

J2000 to TOD Transformation

Returns:

J2000 to ECEF transformation matrix

eci2ecef

public Matrix eci2ecef(double MJD_UT1,
                       double MJD_TT)

ECI to ECEF Transformation

Returns:

ECI to ECEF transformation matrix

eci2ecef

public Matrix eci2ecef(Time t)

ECI to ECEF Transformation

Returns:

ECI to ECEF transformation matrix

update

public void update(double MJD_UT1,
                   double MJD_TT)

Updates the Earth model.

Parameters:

MJD_UT1. - Universal Time in modified julian date

MJD_TT. - Terrestrial Dynamical Time in modified julian date

sunVector

public VectorN sunVector(double MJD_TT)

Computes the Sun's geocentric position using a low precision analytical series.

Returns:

Solar position vector [m] with respect to the mean equator and equinox of J2000 (EME2000, ICRF)

get_JPL_Sun_Vector

public VectorN get_JPL_Sun_Vector()

Return the (precalculated) JPL Sun Vector

Specified by:

get_JPL_Sun_Vector in interface BodyRef

Returns:

Vector from the center of the Earth to the Sun [km].

get_JPL_Moon_Vector

public VectorN get_JPL_Moon_Vector()

Return the (precalculated) JPL Moon Vector

Specified by:

get_JPL_Moon_Vector in interface BodyRef

Returns:

Vector from the center of the Earth to the Moon [km].

get_omega_e

public double get_omega_e(Time t)

Return the dynamic rotation rate of the Earth at the given Time.

Parameters:

t - Time.

Returns:

Omega [rad/s]

get_omega_e

public double get_omega_e(double mjd_ut1)

Return the dynamic rotation rate of the Earth at the given time.

Parameters:

mjd_ut1 - time.

Returns:

Omega [rad/s]

set_use_sun

public void set_use_sun(boolean b)

Set the flag whether to calculate the Sun's position.

Parameters:

b -

set_use_moon

public void set_use_moon(boolean b)

Set the flag whether to calculate the Moon's position.

Parameters:

b -

moonVector

public VectorN moonVector(double MJD_TT)

Computes the Moon's geocentric position using a low precision analytical series.

Returns:

Lunar position vector [m] with respect to the mean equator and equinox of J2000 (EME2000, ICRF).

inertial_to_body

public Matrix inertial_to_body(Time t)

Returns the transformation between inertial and body coordinates.

Specified by:

inertial_to_body in interface BodyRef

Parameters:

mjd_body - Earth referenced time (Universal Time UT1)

mjd_inertial - Dynamical time (Terrestrial Time)

Returns:

Transformation matrix

body_to_inertial

public Matrix body_to_inertial(Time t)

Returns the (precalculated) eci2ecef transformation.

Specified by:

body_to_inertial in interface BodyRef

Parameters:

t - Time object

Returns:

Transformation matrix

See Also:

BodyRef.body_to_inertial(Time)

get_spin_rate

public double get_spin_rate(Time t)

Returnts the dynamic Earth rotation rate.

Specified by:

get_spin_rate in interface BodyRef

Parameters:

t - Time object

Returns:

scalar spin rate [rad/s]

See Also:

jat.spacetime.BodyRef#get_spin_rate()

get_mean_radius

public double get_mean_radius()

Returns the mean Earth Radius.

Specified by:

get_mean_radius in interface BodyRef

Returns:

radius [m]

See Also:

BodyRef.get_mean_radius()

get_grav_const

public double get_grav_const()

Returns the Earth's gravitational constant.

Specified by:

get_grav_const in interface BodyRef

Returns:

grav_constant [m^3/s^2]

See Also:

BodyRef.get_grav_const()

trueOfDate

public Matrix trueOfDate(Time t)

Returns the trueOfDate trasformation.

Specified by:

trueOfDate in interface BodyRef

Parameters:

t - Time object

Returns:

Transformation matrix

See Also:

BodyRef.trueOfDate(jat.spacetime.Time)

main

public static void main(java.lang.String[] args)

Test method. See Vallado example 3-14.

Parameters:

args -