GeographicLib
1.21
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Model of the earth's magnetic field. More...
#include <GeographicLib/MagneticModel.hpp>
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 throw () |
const std::string & | DateTime () const throw () |
const std::string & | MagneticFile () const throw () |
const std::string & | MagneticModelName () const throw () |
const std::string & | MagneticModelDirectory () const throw () |
Math::real | MinHeight () const throw () |
Math::real | MaxHeight () const throw () |
Math::real | MinTime () const throw () |
Math::real | MaxTime () const throw () |
Math::real | MajorRadius () const throw () |
Math::real | Flattening () const throw () |
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 throw () |
void | operator() (real t, real lat, real lon, real h, real &Bx, real &By, real &Bz, real &Bxt, real &Byt, real &Bzt) const throw () |
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) throw () |
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) throw () |
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 // $Id: ab27b155755e540d29e5e6bf550df8cdb00c74ba $ #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.
GeographicLib::MagneticModel::MagneticModel | ( | const std::string & | name, |
const std::string & | path = "" , |
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const Geocentric & | earth = Geocentric::WGS84 |
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) | [explicit] |
Construct a magnetic model.
[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. |
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 may throw an exception because the file does not exist, is unreadable, or is corrupt.
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 specify an ellipsoid to allow geodetic coordinates to the transformed into the spherical coordinates used in the spherical harmonic sum.
Definition at line 44 of file MagneticModel.cpp.
References DefaultMagneticPath(), and GeographicLib::SphericalEngine::coeff::readcoeffs().
void GeographicLib::MagneticModel::operator() | ( | real | t, |
real | lat, | ||
real | lon, | ||
real | h, | ||
real & | Bx, | ||
real & | By, | ||
real & | Bz | ||
) | const throw () [inline] |
Evaluate the components of the geomagnetic field.
[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 131 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 throw () [inline] |
Evaluate the components of the geomagnetic field and their time derivatives
[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 153 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.
[in] | t | the time (years). |
[in] | lat | latitude of the point (degrees). |
[in] | h | the height of the point above the ellipsoid (meters). |
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 207 of file MagneticModel.cpp.
Referenced by main().
static void GeographicLib::MagneticModel::FieldComponents | ( | real | Bx, |
real | By, | ||
real | Bz, | ||
real & | H, | ||
real & | F, | ||
real & | D, | ||
real & | I | ||
) | throw () [inline, static] |
Compute various quantities dependent on the magnetic field.
[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 190 of file MagneticModel.hpp.
Referenced by main().
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 | ||
) | throw () [static] |
Compute various quantities dependent on the magnetic field and its rate of change.
[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 222 of file MagneticModel.cpp.
References GeographicLib::Math::hypot(), and GeographicLib::Math::sq().
const std::string& GeographicLib::MagneticModel::Description | ( | ) | const throw () [inline] |
Definition at line 231 of file MagneticModel.hpp.
Referenced by main().
const std::string& GeographicLib::MagneticModel::DateTime | ( | ) | const throw () [inline] |
Definition at line 237 of file MagneticModel.hpp.
Referenced by main().
const std::string& GeographicLib::MagneticModel::MagneticFile | ( | ) | const throw () [inline] |
Definition at line 242 of file MagneticModel.hpp.
Referenced by main().
const std::string& GeographicLib::MagneticModel::MagneticModelName | ( | ) | const throw () [inline] |
Definition at line 248 of file MagneticModel.hpp.
Referenced by main().
const std::string& GeographicLib::MagneticModel::MagneticModelDirectory | ( | ) | const throw () [inline] |
Definition at line 253 of file MagneticModel.hpp.
Math::real GeographicLib::MagneticModel::MinHeight | ( | ) | const throw () [inline] |
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 264 of file MagneticModel.hpp.
Referenced by main().
Math::real GeographicLib::MagneticModel::MaxHeight | ( | ) | const throw () [inline] |
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 275 of file MagneticModel.hpp.
Referenced by main().
Math::real GeographicLib::MagneticModel::MinTime | ( | ) | const throw () [inline] |
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 286 of file MagneticModel.hpp.
Referenced by main().
Math::real GeographicLib::MagneticModel::MaxTime | ( | ) | const throw () [inline] |
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 297 of file MagneticModel.hpp.
Referenced by main().
Math::real GeographicLib::MagneticModel::MajorRadius | ( | ) | const throw () [inline] |
Definition at line 304 of file MagneticModel.hpp.
Math::real GeographicLib::MagneticModel::Flattening | ( | ) | const throw () [inline] |
Definition at line 310 of file MagneticModel.hpp.
std::string GeographicLib::MagneticModel::DefaultMagneticPath | ( | ) | [static] |
This is the value of the environment variable 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:/Documents and Settings/All Users/Application Data/GeographicLib/magnetic on Windows systems).
Definition at line 237 of file MagneticModel.cpp.
References GEOGRAPHICLIB_DATA.
Referenced by main(), and MagneticModel().
std::string GeographicLib::MagneticModel::DefaultMagneticName | ( | ) | [static] |
This is the value of the environment variable 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 250 of file MagneticModel.cpp.
References MAGNETIC_DEFAULT_NAME.
Referenced by main().