GeographicLib
1.51
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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(), int Nmax=-1, int Mmax=-1) | |
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 | EquatorialRadius () const |
Math::real | Flattening () const |
int | Degree () const |
int | Order () const |
Math::real | MajorRadius () 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) |
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 models and the data format.
See
Example of use:
MagneticField is a command-line utility providing access to the functionality of MagneticModel and MagneticCircle.
Definition at line 75 of file MagneticModel.hpp.
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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(). |
[in] | Nmax | (optional) if non-negative, truncate the degree of the model this value. |
[in] | Mmax | (optional) if non-negative, truncate the order of the model this value. |
GeographicErr | if the data file cannot be found, is unreadable, or is corrupt, or if Mmax > Nmax. |
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.
If Nmax ≥ 0 and Mmax < 0, then Mmax is set to Nmax. After the model is loaded, the maximum degree and order of the model can be found by the Degree() and Order() methods.
Definition at line 37 of file MagneticModel.cpp.
References DefaultMagneticPath(), and GeographicLib::SphericalEngine::coeff::readcoeffs().
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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 155 of file MagneticModel.hpp.
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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 178 of file MagneticModel.hpp.
MagneticCircle GeographicLib::MagneticModel::Circle | ( | real | t, |
real | lat, | ||
real | h | ||
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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). |
std::bad_alloc | if the memory necessary for creating a MagneticCircle can't be allocated. |
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 224 of file MagneticModel.cpp.
Referenced by main().
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inlinestatic |
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 217 of file MagneticModel.hpp.
Referenced by main().
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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 245 of file MagneticModel.cpp.
References GeographicLib::Math::atan2d(), GeographicLib::Math::degree(), and GeographicLib::Math::sq().
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Definition at line 258 of file MagneticModel.hpp.
Referenced by main().
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Definition at line 264 of file MagneticModel.hpp.
Referenced by main().
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Definition at line 269 of file MagneticModel.hpp.
Referenced by main().
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Definition at line 275 of file MagneticModel.hpp.
Referenced by main().
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Definition at line 280 of file MagneticModel.hpp.
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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 291 of file MagneticModel.hpp.
Referenced by main().
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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 302 of file MagneticModel.hpp.
Referenced by main().
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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 313 of file MagneticModel.hpp.
Referenced by main().
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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 324 of file MagneticModel.hpp.
Referenced by main().
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Definition at line 331 of file MagneticModel.hpp.
References GeographicLib::Geocentric::EquatorialRadius().
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Definition at line 337 of file MagneticModel.hpp.
References GeographicLib::Geocentric::Flattening().
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Definition at line 342 of file MagneticModel.hpp.
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Definition at line 347 of file MagneticModel.hpp.
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Definition at line 353 of file MagneticModel.hpp.
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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 260 of file MagneticModel.cpp.
References GEOGRAPHICLIB_DATA.
Referenced by MagneticModel(), and main().
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This is the value of the environment variable GEOGRAPHICLIB_MAGNETIC_NAME, if set; otherwise, it is "wmm2020". 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 273 of file MagneticModel.cpp.
References GEOGRAPHICLIB_MAGNETIC_DEFAULT_NAME.
Referenced by main().