org.orekit.models.earth

Class GeoMagneticField

java.lang.Object

org.orekit.models.earth.GeoMagneticField

public class GeoMagneticField
extends Object

Used to calculate the geomagnetic field at a given geodetic point on earth. The calculation is estimated using spherical harmonic expansion of the geomagnetic potential with coefficients provided by an actual geomagnetic field model (e.g. IGRF, WMM).

Based on original software written by Manoj Nair from the National Geophysical Data Center, NOAA, as part of the WMM 2010 software release (WMM_SubLibrary.c)

Author:

Thomas Neidhart

See Also:

World Magnetic Model Overview, WMM Software Downloads

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	GeoMagneticField(String modelName, double epoch, int maxN, int maxNSec, double validityStart, double validityEnd) Create a new geomagnetic field model with the given parameters.

Method Summary

Modifier and Type	Method and Description
GeoMagneticElements	calculateField(double latitude, double longitude, double height) Calculate the magnetic field at the specified geodetic point identified by latitude, longitude and altitude.
static double	getDecimalYear(int day, int month, int year) Utility function to get a decimal year for a given day.
double	getEpoch() Returns the epoch for this magnetic field model.
String	getModelName() Returns the model name.
protected void	setMainFieldCoefficients(int n, int m, double gnm, double hnm) Set the given main field coefficients.
protected void	setSecularVariationCoefficients(int n, int m, double dgnm, double dhnm) Set the given secular variation coefficients.
boolean	supportsTimeTransform() Indicates whether this model supports time transformation or not.
GeoMagneticField	transformModel(double year) Time transform the model coefficients from the base year of the model using secular variation coefficients.
GeoMagneticField	transformModel(GeoMagneticField otherModel, double year) Time transform the model coefficients from the base year of the model using a linear interpolation with a second model.
double	validFrom() Returns the start of the validity period for this model.
double	validTo() Returns the end of the validity period for this model.

Methods inherited from class java.lang.Object

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

Constructor Detail

GeoMagneticField

protected GeoMagneticField(String modelName,
                           double epoch,
                           int maxN,
                           int maxNSec,
                           double validityStart,
                           double validityEnd)

Create a new geomagnetic field model with the given parameters. Internal structures are initialized according to the specified degrees of the main and secular variations.

Parameters:

modelName - the model name

epoch - the epoch of the model

maxN - the maximum degree of the main model

maxNSec - the maximum degree of the secular variations

validityStart - validity start of this model

validityEnd - validity end of this model

Method Detail

getEpoch

public double getEpoch()

Returns the epoch for this magnetic field model.

Returns:

the epoch

getModelName

public String getModelName()

Returns the model name.

Returns:

the model name

validFrom

public double validFrom()

Returns the start of the validity period for this model.

Returns:

the validity start as decimal year

validTo

public double validTo()

Returns the end of the validity period for this model.

Returns:

the validity end as decimal year

supportsTimeTransform

public boolean supportsTimeTransform()

Indicates whether this model supports time transformation or not.

Returns:

true if this model can be transformed within its validity period, false otherwise

setMainFieldCoefficients

protected void setMainFieldCoefficients(int n,
                                        int m,
                                        double gnm,
                                        double hnm)

Set the given main field coefficients.

Parameters:

n - the n index

m - the m index

gnm - the g coefficient at position n,m

hnm - the h coefficient at position n,m

setSecularVariationCoefficients

protected void setSecularVariationCoefficients(int n,
                                               int m,
                                               double dgnm,
                                               double dhnm)

Set the given secular variation coefficients.

Parameters:

n - the n index

m - the m index

dgnm - the dg coefficient at position n,m

dhnm - the dh coefficient at position n,m

calculateField

public GeoMagneticElements calculateField(double latitude,
                                          double longitude,
                                          double height)

Calculate the magnetic field at the specified geodetic point identified by latitude, longitude and altitude.

Parameters:

latitude - the WGS84 latitude in decimal degrees

longitude - the WGS84 longitude in decimal degrees

height - the height above the WGS84 ellipsoid in kilometers

Returns:

the GeoMagneticElements at the given geodetic point

transformModel

public GeoMagneticField transformModel(double year)
                                throws OrekitException

Time transform the model coefficients from the base year of the model using secular variation coefficients.

Parameters:

year - the year to which the model shall be transformed

Returns:

a time-transformed magnetic field model

Throws:

OrekitException - if the specified year is outside the validity period of the model or the model does not support time transformations (i.e. no secular variations available)

transformModel

public GeoMagneticField transformModel(GeoMagneticField otherModel,
                                       double year)
                                throws OrekitException

Time transform the model coefficients from the base year of the model using a linear interpolation with a second model. The second model is required to have an adjacent validity period.

Parameters:

otherModel - the other magnetic field model

year - the year to which the model shall be transformed

Returns:

a time-transformed magnetic field model

Throws:

OrekitException - if the specified year is outside the validity period of the model or the model does not support time transformations (i.e. no secular variations available)

getDecimalYear

public static double getDecimalYear(int day,
                                    int month,
                                    int year)

Utility function to get a decimal year for a given day.

Parameters:

day - the day (1-31)

month - the month (1-12)

year - the year

Returns:

the decimal year represented by the given day