GeographicLib::MagneticModel Class Reference

Model of the earth's magnetic field. More...

#include <GeographicLib/MagneticModel.hpp>

List of all members.

Public Member Functions

Setting up the magnetic model



 MagneticModel (const std::string &name, const std::string &path="", const Geocentric &earth=Geocentric::WGS84())
Inspector functions



const std::string & Description () const
const std::string & DateTime () const
const std::string & MagneticFile () const
const std::string & MagneticModelName () const
const std::string & MagneticModelDirectory () const
Math::real MinHeight () const
Math::real MaxHeight () const
Math::real MinTime () const
Math::real MaxTime () const
Math::real MajorRadius () const
Math::real Flattening () const

Static Public Member Functions

static std::string DefaultMagneticPath ()
static std::string DefaultMagneticName ()

Compute the magnetic field



void operator() (real t, real lat, real lon, real h, real &Bx, real &By, real &Bz) const
void operator() (real t, real lat, real lon, real h, real &Bx, real &By, real &Bz, real &Bxt, real &Byt, real &Bzt) const
MagneticCircle Circle (real t, real lat, real h) const
static void FieldComponents (real Bx, real By, real Bz, real &H, real &F, real &D, real &I)
static void FieldComponents (real Bx, real By, real Bz, real Bxt, real Byt, real Bzt, real &H, real &F, real &D, real &I, real &Ht, real &Ft, real &Dt, real &It)

Detailed Description

Model of the earth's magnetic field.

Evaluate the earth's magnetic field according to a model. At present only internal magnetic fields are handled. These are due to the earth's code and crust; these vary slowly (over many years). Excluded are the effects of currents in the ionosphere and magnetosphere which have daily and annual variations.

See Magnetic models for details of how to install the magnetic model and the data format.

See

Example of use:

// Example of using the GeographicLib::MagneticModel class

#include <iostream>
#include <exception>
#include <GeographicLib/MagneticModel.hpp>

using namespace std;
using namespace GeographicLib;

int main() {
  try {
    MagneticModel mag("wmm2010");
    double lat = 27.99, lon = 86.93, h = 8820, t = 2012; // Mt Everest
    double Bx, By, Bz;
    mag(t, lat,lon, h, Bx, By, Bz);
    double H, F, D, I;
    MagneticModel::FieldComponents(Bx, By, Bz, H, F, D, I);
    cout << H << " " << F << " " << D << " " << I << "\n";
  }
  catch (const exception& e) {
    cerr << "Caught exception: " << e.what() << "\n";
    return 1;
  }
  return 0;
}

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

Definition at line 60 of file MagneticModel.hpp.


Constructor & Destructor Documentation

GeographicLib::MagneticModel::MagneticModel ( const std::string &  name,
const std::string &  path = "",
const Geocentric earth = Geocentric::WGS84() 
) [explicit]

Construct a magnetic model.

Parameters:
[in] name the name of the model.
[in] path (optional) directory for data file.
[in] earth (optional) Geocentric object for converting coordinates; default Geocentric::WGS84().
Exceptions:
GeographicErr if the data file cannot be found, is unreadable, or is corrupt.
std::bad_alloc if the memory necessary for storing the model can't be allocated.

A filename is formed by appending ".wmm" (World Magnetic Model) to the name. If path is specified (and is non-empty), then the file is loaded from directory, path. Otherwise the path is given by the DefaultMagneticPath().

This file contains the metadata which specifies the properties of the model. The coefficients for the spherical harmonic sums are obtained from a file obtained by appending ".cof" to metadata file (so the filename ends in ".wwm.cof").

The model is not tied to a particular ellipsoidal model of the earth. The final earth argument to the constructor specifies an ellipsoid to allow geodetic coordinates to the transformed into the spherical coordinates used in the spherical harmonic sum.

Definition at line 37 of file MagneticModel.cpp.

References DefaultMagneticPath(), and GeographicLib::SphericalEngine::coeff::readcoeffs().


Member Function Documentation

void GeographicLib::MagneticModel::operator() ( real  t,
real  lat,
real  lon,
real  h,
real &  Bx,
real &  By,
real &  Bz 
) const [inline]

Evaluate the components of the geomagnetic field.

Parameters:
[in] t the time (years).
[in] lat latitude of the point (degrees).
[in] lon longitude of the point (degrees).
[in] h the height of the point above the ellipsoid (meters).
[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 130 of file MagneticModel.hpp.

void GeographicLib::MagneticModel::operator() ( real  t,
real  lat,
real  lon,
real  h,
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

Parameters:
[in] t the time (years).
[in] lat latitude of the point (degrees).
[in] lon longitude of the point (degrees).
[in] h the height of the point above the ellipsoid (meters).
[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 152 of file MagneticModel.hpp.

MagneticCircle GeographicLib::MagneticModel::Circle ( real  t,
real  lat,
real  h 
) const

Create a MagneticCircle object to allow the geomagnetic field at many points with constant lat, h, and t and varying lon to be computed efficiently.

Parameters:
[in] t the time (years).
[in] lat latitude of the point (degrees).
[in] h the height of the point above the ellipsoid (meters).
Exceptions:
std::bad_alloc if the memory necessary for creating a MagneticCircle can't be allocated.
Returns:
a MagneticCircle object whose MagneticCircle::operator()(real lon) member function computes the field at particular values of lon.

If the field at several points on a circle of latitude need to be calculated then creating a MagneticCircle and using its member functions will be substantially faster, especially for high-degree models.

Definition at line 202 of file MagneticModel.cpp.

static void GeographicLib::MagneticModel::FieldComponents ( real  Bx,
real  By,
real  Bz,
real &  H,
real &  F,
real &  D,
real &  I 
) [inline, static]

Compute various quantities dependent on the magnetic field.

Parameters:
[in] Bx the x (easterly) component of the magnetic field (nT).
[in] By the y (northerly) component of the magnetic field (nT).
[in] Bz the z (vertical, up positive) component of the magnetic field (nT).
[out] H the horizontal magnetic field (nT).
[out] F the total magnetic field (nT).
[out] D the declination of the field (degrees east of north).
[out] I the inclination of the field (degrees down from horizontal).

Definition at line 191 of file MagneticModel.hpp.

void GeographicLib::MagneticModel::FieldComponents ( real  Bx,
real  By,
real  Bz,
real  Bxt,
real  Byt,
real  Bzt,
real &  H,
real &  F,
real &  D,
real &  I,
real &  Ht,
real &  Ft,
real &  Dt,
real &  It 
) [static]

Compute various quantities dependent on the magnetic field and its rate of change.

Parameters:
[in] Bx the x (easterly) component of the magnetic field (nT).
[in] By the y (northerly) component of the magnetic field (nT).
[in] Bz the z (vertical, up positive) component of the magnetic field (nT).
[in] Bxt the rate of change of Bx (nT/yr).
[in] Byt the rate of change of By (nT/yr).
[in] Bzt the rate of change of Bz (nT/yr).
[out] H the horizontal magnetic field (nT).
[out] F the total magnetic field (nT).
[out] D the declination of the field (degrees east of north).
[out] I the inclination of the field (degrees down from horizontal).
[out] Ht the rate of change of H (nT/yr).
[out] Ft the rate of change of F (nT/yr).
[out] Dt the rate of change of D (degrees/yr).
[out] It the rate of change of I (degrees/yr).

Definition at line 217 of file MagneticModel.cpp.

References GeographicLib::Math::degree(), GeographicLib::Math::hypot(), and GeographicLib::Math::sq().

const std::string& GeographicLib::MagneticModel::Description (  )  const [inline]
Returns:
the description of the magnetic model, if available, from the Description file in the data file; if absent, return "NONE".

Definition at line 232 of file MagneticModel.hpp.

const std::string& GeographicLib::MagneticModel::DateTime (  )  const [inline]
Returns:
date of the model, if available, from the ReleaseDate field in the data file; if absent, return "UNKNOWN".

Definition at line 238 of file MagneticModel.hpp.

const std::string& GeographicLib::MagneticModel::MagneticFile (  )  const [inline]
Returns:
full file name used to load the magnetic model.

Definition at line 243 of file MagneticModel.hpp.

const std::string& GeographicLib::MagneticModel::MagneticModelName (  )  const [inline]
Returns:
"name" used to load the magnetic model (from the first argument of the constructor, but this may be overridden by the model file).

Definition at line 249 of file MagneticModel.hpp.

const std::string& GeographicLib::MagneticModel::MagneticModelDirectory (  )  const [inline]
Returns:
directory used to load the magnetic model.

Definition at line 254 of file MagneticModel.hpp.

Math::real GeographicLib::MagneticModel::MinHeight (  )  const [inline]
Returns:
the minimum height above the ellipsoid (in meters) for which this MagneticModel should be used.

Because the model will typically provide useful results slightly outside the range of allowed heights, no check of t argument is made by MagneticModel::operator()() or MagneticModel::Circle.

Definition at line 265 of file MagneticModel.hpp.

Math::real GeographicLib::MagneticModel::MaxHeight (  )  const [inline]
Returns:
the maximum height above the ellipsoid (in meters) for which this MagneticModel should be used.

Because the model will typically provide useful results slightly outside the range of allowed heights, no check of t argument is made by MagneticModel::operator()() or MagneticModel::Circle.

Definition at line 276 of file MagneticModel.hpp.

Math::real GeographicLib::MagneticModel::MinTime (  )  const [inline]
Returns:
the minimum time (in years) for which this MagneticModel should be used.

Because the model will typically provide useful results slightly outside the range of allowed times, no check of t argument is made by MagneticModel::operator()() or MagneticModel::Circle.

Definition at line 287 of file MagneticModel.hpp.

Math::real GeographicLib::MagneticModel::MaxTime (  )  const [inline]
Returns:
the maximum time (in years) for which this MagneticModel should be used.

Because the model will typically provide useful results slightly outside the range of allowed times, no check of t argument is made by MagneticModel::operator()() or MagneticModel::Circle.

Definition at line 298 of file MagneticModel.hpp.

Math::real GeographicLib::MagneticModel::MajorRadius (  )  const [inline]
Returns:
a the equatorial radius of the ellipsoid (meters). This is the value of a inherited from the Geocentric object used in the constructor.

Definition at line 305 of file MagneticModel.hpp.

Math::real GeographicLib::MagneticModel::Flattening (  )  const [inline]
Returns:
f the flattening of the ellipsoid. This is the value inherited from the Geocentric object used in the constructor.

Definition at line 311 of file MagneticModel.hpp.

std::string GeographicLib::MagneticModel::DefaultMagneticPath (  )  [static]
Returns:
the default path for magnetic model data files.

This is the value of the environment variable GEOGRAPHICLIB_MAGNETIC_PATH, if set; otherwise, it is $GEOGRAPHICLIB_DATA/magnetic if the environment variable GEOGRAPHICLIB_DATA is set; otherwise, it is a compile-time default (/usr/local/share/GeographicLib/magnetic on non-Windows systems and C:/ProgramData/GeographicLib/magnetic on Windows systems).

Definition at line 232 of file MagneticModel.cpp.

References GEOGRAPHICLIB_DATA.

Referenced by MagneticModel().

std::string GeographicLib::MagneticModel::DefaultMagneticName (  )  [static]
Returns:
the default name for the magnetic model.

This is the value of the environment variable GEOGRAPHICLIB_MAGNETIC_NAME, if set; otherwise, it is "wmm2010". The MagneticModel class does not use this function; it is just provided as a convenience for a calling program when constructing a MagneticModel object.

Definition at line 245 of file MagneticModel.cpp.

References GEOGRAPHICLIB_MAGNETIC_DEFAULT_NAME.


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