GeographicLib::MagneticCircle Class Reference

Geomagnetic field on a circle of latitude. More...

#include <GeographicLib/MagneticCircle.hpp>

Public Member Functions
	MagneticCircle ()
Compute the magnetic field
void	operator() (real lon, real &Bx, real &By, real &Bz) const
void	operator() (real lon, real &Bx, real &By, real &Bz, real &Bxt, real &Byt, real &Bzt) const
void	FieldGeocentric (real lon, real &BX, real &BY, real &BZ, real &BXt, real &BYt, real &BZt) const
Inspector functions
bool	Init () const
Math::real	EquatorialRadius () const
Math::real	Flattening () const
Math::real	Latitude () const
Math::real	Height () const
Math::real	Time () const

Friends
class	MagneticModel

Detailed Description

Geomagnetic field on a circle of latitude.

Evaluate the earth's magnetic field on a circle of constant height and latitude. This uses a CircularEngine to pre-evaluate the inner sum of the spherical harmonic sum, allowing the values of the field at several different longitudes to be evaluated rapidly.

Use MagneticModel::Circle to create a MagneticCircle object. (The constructor for this class is private.)

Example of use:

// Example of using the GeographicLib::MagneticCircle class
// This requires that the wmm2010 magnetic model be installed; see
// https://geographiclib.sourceforge.io/C++/doc/magnetic.html#magneticinst
 
#include <iostream>
#include <exception>
#include <GeographicLib/MagneticModel.hpp>
#include <GeographicLib/MagneticCircle.hpp>
 
using namespace std;
using namespace GeographicLib;
 
int main() {
  try {
    MagneticModel mag("wmm2010");
    double lat = 27.99, lon0 = 86.93, h = 8820, t = 2012; // Mt Everest
    {
      // Slow method of evaluating the values at several points on a circle of
      // latitude.
      for (int i = -5; i <= 5; ++i) {
        double lon = lon0 + i * 0.2;
        double Bx, By, Bz;
        mag(t, lat, lon, h, Bx, By, Bz);
        cout << lon << " " << Bx << " " << By << " " << Bz << "\n";
      }
    }
    {
      // Fast method of evaluating the values at several points on a circle of
      // latitude using MagneticCircle.
      MagneticCircle circ = mag.Circle(t, lat, h);
      for (int i = -5; i <= 5; ++i) {
        double lon = lon0 + i * 0.2;
        double Bx, By, Bz;
        circ(lon, Bx, By, Bz);
        cout << lon << " " << Bx << " " << By << " " << Bz << "\n";
      }
    }
  }
  catch (const exception& e) {
    cerr << "Caught exception: " << e.what() << "\n";
    return 1;
  }
}

MagneticField is a command-line utility providing access to the functionality of MagneticModel and MagneticCircle.

Definition at line 37 of file MagneticCircle.hpp.

Constructor & Destructor Documentation

MagneticCircle()

GeographicLib::MagneticCircle::MagneticCircle ( )

inline

A default constructor for the normal gravity. This sets up an uninitialized object which can be later replaced by the MagneticModel::Circle.

Definition at line 102 of file MagneticCircle.hpp.

Member Function Documentation

operator()() [1/2]

void GeographicLib::MagneticCircle::operator() ( real  lon, real &  Bx, real &  By, real &  Bz  ) const

inline

Evaluate the components of the geomagnetic field at a particular longitude.

Parameters

[in]	lon	longitude of the point (degrees).
[out]	Bx	the easterly component of the magnetic field (nanotesla).
[out]	By	the northerly component of the magnetic field (nanotesla).
[out]	Bz	the vertical (up) component of the magnetic field (nanotesla).

Definition at line 118 of file MagneticCircle.hpp.

operator()() [2/2]

void GeographicLib::MagneticCircle::operator() ( real  lon, real &  Bx, real &  By, real &  Bz, real &  Bxt, real &  Byt, real &  Bzt  ) const

inline

Evaluate the components of the geomagnetic field and their time derivatives at a particular longitude.

Parameters

[in]	lon	longitude of the point (degrees).
[out]	Bx	the easterly component of the magnetic field (nanotesla).
[out]	By	the northerly component of the magnetic field (nanotesla).
[out]	Bz	the vertical (up) component of the magnetic field (nanotesla).
[out]	Bxt	the rate of change of Bx (nT/yr).
[out]	Byt	the rate of change of By (nT/yr).
[out]	Bzt	the rate of change of Bz (nT/yr).

Definition at line 137 of file MagneticCircle.hpp.

FieldGeocentric()

void GeographicLib::MagneticCircle::FieldGeocentric	(	real	lon,
		real &	BX,
		real &	BY,
		real &	BZ,
		real &	BXt,
		real &	BYt,
		real &	BZt
	)		const

Evaluate the components of the geomagnetic field and their time derivatives at a particular longitude.

Parameters

[in]	lon	longitude of the point (degrees).
[out]	BX	the X component of the magnetic field (nT).
[out]	BY	the Y component of the magnetic field (nT).
[out]	BZ	the Z component of the magnetic field (nT).
[out]	BXt	the rate of change of BX (nT/yr).
[out]	BYt	the rate of change of BY (nT/yr).
[out]	BZt	the rate of change of BZ (nT/yr).

Definition at line 45 of file MagneticCircle.cpp.

References GeographicLib::Math::sincosd().

Init()

bool GeographicLib::MagneticCircle::Init ( ) const

inline

Returns

true if the object has been initialized.

Definition at line 164 of file MagneticCircle.hpp.

EquatorialRadius()

Math::real GeographicLib::MagneticCircle::EquatorialRadius ( ) const

inline

Returns

a the equatorial radius of the ellipsoid (meters). This is the value inherited from the MagneticModel object used in the constructor.

Definition at line 170 of file MagneticCircle.hpp.

References GeographicLib::Math::NaN().

Flattening()

Math::real GeographicLib::MagneticCircle::Flattening ( ) const

inline

Returns

f the flattening of the ellipsoid. This is the value inherited from the MagneticModel object used in the constructor.

Definition at line 176 of file MagneticCircle.hpp.

References GeographicLib::Math::NaN().

Latitude()

Math::real GeographicLib::MagneticCircle::Latitude ( ) const

inline

Returns

the latitude of the circle (degrees).

Definition at line 181 of file MagneticCircle.hpp.

References GeographicLib::Math::NaN().

Height()

Math::real GeographicLib::MagneticCircle::Height ( ) const

inline

Returns

the height of the circle (meters).

Definition at line 186 of file MagneticCircle.hpp.

References GeographicLib::Math::NaN().

Time()

Math::real GeographicLib::MagneticCircle::Time ( ) const

inline

Returns

the time (fractional years).

Definition at line 191 of file MagneticCircle.hpp.

References GeographicLib::Math::NaN().

Friends And Related Function Documentation

MagneticModel

friend class MagneticModel

friend

Definition at line 93 of file MagneticCircle.hpp.

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The documentation for this class was generated from the following files:

• MagneticCircle.hpp
• MagneticCircle.cpp