205 lines
7.5 KiB
C++
205 lines
7.5 KiB
C++
/**
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* \file MagneticCircle.hpp
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* \brief Header for GeographicLib::MagneticCircle class
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*
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* Copyright (c) Charles Karney (2011-2021) <charles@karney.com> and licensed
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* under the MIT/X11 License. For more information, see
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* https://geographiclib.sourceforge.io/
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**********************************************************************/
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#if !defined(GEOGRAPHICLIB_MAGNETICCIRCLE_HPP)
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#define GEOGRAPHICLIB_MAGNETICCIRCLE_HPP 1
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#include <vector>
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#include <GeographicLib/Constants.hpp>
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#include <GeographicLib/CircularEngine.hpp>
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namespace GeographicLib {
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/**
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* \brief Geomagnetic field on a circle of latitude
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*
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* Evaluate the earth's magnetic field on a circle of constant height and
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* latitude. This uses a CircularEngine to pre-evaluate the inner sum of the
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* spherical harmonic sum, allowing the values of the field at several
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* different longitudes to be evaluated rapidly.
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*
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* Use MagneticModel::Circle to create a MagneticCircle object. (The
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* constructor for this class is private.)
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*
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* Example of use:
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* \include example-MagneticCircle.cpp
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*
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* <a href="MagneticField.1.html">MagneticField</a> is a command-line utility
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* providing access to the functionality of MagneticModel and MagneticCircle.
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**********************************************************************/
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class GEOGRAPHICLIB_EXPORT MagneticCircle {
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private:
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typedef Math::real real;
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real _a, _f, _lat, _h, _t, _cphi, _sphi, _t1, _dt0;
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bool _interpolate, _constterm;
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CircularEngine _circ0, _circ1, _circ2;
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MagneticCircle(real a, real f, real lat, real h, real t,
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real cphi, real sphi, real t1, real dt0,
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bool interpolate,
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const CircularEngine& circ0, const CircularEngine& circ1)
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: _a(a)
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, _f(f)
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, _lat(Math::LatFix(lat))
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, _h(h)
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, _t(t)
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, _cphi(cphi)
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, _sphi(sphi)
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, _t1(t1)
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, _dt0(dt0)
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, _interpolate(interpolate)
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, _constterm(false)
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, _circ0(circ0)
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, _circ1(circ1)
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{}
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MagneticCircle(real a, real f, real lat, real h, real t,
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real cphi, real sphi, real t1, real dt0,
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bool interpolate,
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const CircularEngine& circ0, const CircularEngine& circ1,
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const CircularEngine& circ2)
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: _a(a)
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, _f(f)
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, _lat(lat)
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, _h(h)
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, _t(t)
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, _cphi(cphi)
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, _sphi(sphi)
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, _t1(t1)
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, _dt0(dt0)
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, _interpolate(interpolate)
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, _constterm(true)
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, _circ0(circ0)
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, _circ1(circ1)
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, _circ2(circ2)
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{}
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void Field(real lon, bool diffp,
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real& Bx, real& By, real& Bz,
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real& Bxt, real& Byt, real& Bzt) const;
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void FieldGeocentric(real slam, real clam,
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real& BX, real& BY, real& BZ,
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real& BXt, real& BYt, real& BZt) const;
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friend class MagneticModel; // MagneticModel calls the private constructor
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public:
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/**
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* A default constructor for the normal gravity. This sets up an
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* uninitialized object which can be later replaced by the
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* MagneticModel::Circle.
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**********************************************************************/
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MagneticCircle() : _a(-1) {}
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/** \name Compute the magnetic field
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**********************************************************************/
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///@{
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/**
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* Evaluate the components of the geomagnetic field at a particular
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* longitude.
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*
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* @param[in] lon longitude of the point (degrees).
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* @param[out] Bx the easterly component of the magnetic field (nanotesla).
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* @param[out] By the northerly component of the magnetic field
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* (nanotesla).
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* @param[out] Bz the vertical (up) component of the magnetic field
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* (nanotesla).
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**********************************************************************/
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void operator()(real lon, real& Bx, real& By, real& Bz) const {
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real dummy;
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Field(lon, false, Bx, By, Bz, dummy, dummy, dummy);
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}
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/**
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* Evaluate the components of the geomagnetic field and their time
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* derivatives at a particular longitude.
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*
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* @param[in] lon longitude of the point (degrees).
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* @param[out] Bx the easterly component of the magnetic field (nanotesla).
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* @param[out] By the northerly component of the magnetic field
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* (nanotesla).
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* @param[out] Bz the vertical (up) component of the magnetic field
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* (nanotesla).
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* @param[out] Bxt the rate of change of \e Bx (nT/yr).
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* @param[out] Byt the rate of change of \e By (nT/yr).
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* @param[out] Bzt the rate of change of \e Bz (nT/yr).
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**********************************************************************/
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void operator()(real lon, real& Bx, real& By, real& Bz,
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real& Bxt, real& Byt, real& Bzt) const {
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Field(lon, true, Bx, By, Bz, Bxt, Byt, Bzt);
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}
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/**
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* Evaluate the components of the geomagnetic field and their time
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* derivatives at a particular longitude.
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*
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* @param[in] lon longitude of the point (degrees).
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* @param[out] BX the \e X component of the magnetic field (nT).
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* @param[out] BY the \e Y component of the magnetic field (nT).
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* @param[out] BZ the \e Z component of the magnetic field (nT).
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* @param[out] BXt the rate of change of \e BX (nT/yr).
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* @param[out] BYt the rate of change of \e BY (nT/yr).
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* @param[out] BZt the rate of change of \e BZ (nT/yr).
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**********************************************************************/
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void FieldGeocentric(real lon, real& BX, real& BY, real& BZ,
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real& BXt, real& BYt, real& BZt) const;
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///@}
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/** \name Inspector functions
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**********************************************************************/
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///@{
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/**
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* @return true if the object has been initialized.
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**********************************************************************/
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bool Init() const { return _a > 0; }
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/**
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* @return \e a the equatorial radius of the ellipsoid (meters). This is
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* the value inherited from the MagneticModel object used in the
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* constructor.
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**********************************************************************/
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Math::real EquatorialRadius() const
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{ return Init() ? _a : Math::NaN(); }
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/**
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* @return \e f the flattening of the ellipsoid. This is the value
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* inherited from the MagneticModel object used in the constructor.
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**********************************************************************/
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Math::real Flattening() const
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{ return Init() ? _f : Math::NaN(); }
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/**
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* @return the latitude of the circle (degrees).
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**********************************************************************/
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Math::real Latitude() const
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{ return Init() ? _lat : Math::NaN(); }
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/**
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* @return the height of the circle (meters).
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**********************************************************************/
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Math::real Height() const
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{ return Init() ? _h : Math::NaN(); }
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/**
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* @return the time (fractional years).
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**********************************************************************/
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Math::real Time() const
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{ return Init() ? _t : Math::NaN(); }
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/**
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* \deprecated An old name for EquatorialRadius().
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**********************************************************************/
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GEOGRAPHICLIB_DEPRECATED("Use EquatorialRadius()")
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Math::real MajorRadius() const { return EquatorialRadius(); }
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///@}
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};
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} // namespace GeographicLib
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#endif // GEOGRAPHICLIB_MAGNETICCIRCLE_HPP
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