MagneticModel.cpp
Go to the documentation of this file.
/**
* \file MagneticModel.cpp
* \brief Implementation for GeographicLib::MagneticModel class
*
* Copyright (c) Charles Karney (2011-2021) <karney@alum.mit.edu> and licensed
* under the MIT/X11 License. For more information, see
* https://geographiclib.sourceforge.io/
**********************************************************************/
#include <GeographicLib/MagneticModel.hpp>
#include <fstream>
#include <GeographicLib/SphericalEngine.hpp>
#include <GeographicLib/MagneticCircle.hpp>
#include <GeographicLib/Utility.hpp>
#if !defined(GEOGRAPHICLIB_DATA)
# if defined(_WIN32)
# define GEOGRAPHICLIB_DATA "C:/ProgramData/GeographicLib"
# else
# define GEOGRAPHICLIB_DATA "/usr/local/share/GeographicLib"
# endif
#endif
#if !defined(GEOGRAPHICLIB_MAGNETIC_DEFAULT_NAME)
# define GEOGRAPHICLIB_MAGNETIC_DEFAULT_NAME "wmm2020"
#endif
#if defined(_MSC_VER)
// Squelch warnings about unsafe use of getenv
# pragma warning (disable: 4996)
#endif
namespace GeographicLib {
using namespace std;
MagneticModel::MagneticModel(const std::string& name, const std::string& path,
const Geocentric& earth, int Nmax, int Mmax)
: _name(name)
, _dir(path)
, _description("NONE")
, _date("UNKNOWN")
, _t0(Math::NaN())
, _dt0(1)
, _tmin(Math::NaN())
, _tmax(Math::NaN())
, _a(Math::NaN())
, _hmin(Math::NaN())
, _hmax(Math::NaN())
, _nNmodels(1)
, _nNconstants(0)
, _nmx(-1)
, _mmx(-1)
, _norm(SphericalHarmonic::SCHMIDT)
, _earth(earth)
{
if (_dir.empty())
_dir = DefaultMagneticPath();
bool truncate = Nmax >= 0 || Mmax >= 0;
if (truncate) {
if (Nmax >= 0 && Mmax < 0) Mmax = Nmax;
if (Nmax < 0) Nmax = numeric_limits<int>::max();
if (Mmax < 0) Mmax = numeric_limits<int>::max();
}
ReadMetadata(_name);
_gG.resize(_nNmodels + 1 + _nNconstants);
_hH.resize(_nNmodels + 1 + _nNconstants);
{
string coeff = _filename + ".cof";
ifstream coeffstr(coeff.c_str(), ios::binary);
if (!coeffstr.good())
throw GeographicErr("Error opening " + coeff);
char id[idlength_ + 1];
coeffstr.read(id, idlength_);
if (!coeffstr.good())
throw GeographicErr("No header in " + coeff);
id[idlength_] = '\0';
if (_id != string(id))
throw GeographicErr("ID mismatch: " + _id + " vs " + id);
for (int i = 0; i < _nNmodels + 1 + _nNconstants; ++i) {
int N, M;
if (truncate) { N = Nmax; M = Mmax; }
SphericalEngine::coeff::readcoeffs(coeffstr, N, M, _gG[i], _hH[i],
truncate);
if (!(M < 0 || _gG[i][0] == 0))
throw GeographicErr("A degree 0 term is not permitted");
_harm.push_back(SphericalHarmonic(_gG[i], _hH[i], N, N, M, _a, _norm));
_nmx = max(_nmx, _harm.back().Coefficients().nmx());
_mmx = max(_mmx, _harm.back().Coefficients().mmx());
}
int pos = int(coeffstr.tellg());
coeffstr.seekg(0, ios::end);
if (pos != coeffstr.tellg())
throw GeographicErr("Extra data in " + coeff);
}
}
void MagneticModel::ReadMetadata(const string& name) {
const char* spaces = " \t\n\v\f\r";
_filename = _dir + "/" + name + ".wmm";
ifstream metastr(_filename.c_str());
if (!metastr.good())
throw GeographicErr("Cannot open " + _filename);
string line;
getline(metastr, line);
if (!(line.size() >= 6 && line.substr(0,5) == "WMMF-"))
throw GeographicErr(_filename + " does not contain WMMF-n signature");
string::size_type n = line.find_first_of(spaces, 5);
if (n != string::npos)
n -= 5;
string version(line, 5, n);
if (!(version == "1" || version == "2"))
throw GeographicErr("Unknown version in " + _filename + ": " + version);
string key, val;
while (getline(metastr, line)) {
if (!Utility::ParseLine(line, key, val))
continue;
// Process key words
if (key == "Name")
_name = val;
else if (key == "Description")
_description = val;
else if (key == "ReleaseDate")
_date = val;
else if (key == "Radius")
_a = Utility::val<real>(val);
else if (key == "Type") {
if (!(val == "Linear" || val == "linear"))
throw GeographicErr("Only linear models are supported");
} else if (key == "Epoch")
_t0 = Utility::val<real>(val);
else if (key == "DeltaEpoch")
_dt0 = Utility::val<real>(val);
else if (key == "NumModels")
_nNmodels = Utility::val<int>(val);
else if (key == "NumConstants")
_nNconstants = Utility::val<int>(val);
else if (key == "MinTime")
_tmin = Utility::val<real>(val);
else if (key == "MaxTime")
_tmax = Utility::val<real>(val);
else if (key == "MinHeight")
_hmin = Utility::val<real>(val);
else if (key == "MaxHeight")
_hmax = Utility::val<real>(val);
else if (key == "Normalization") {
if (val == "FULL" || val == "Full" || val == "full")
_norm = SphericalHarmonic::FULL;
else if (val == "SCHMIDT" || val == "Schmidt" || val == "schmidt")
_norm = SphericalHarmonic::SCHMIDT;
else
throw GeographicErr("Unknown normalization " + val);
} else if (key == "ByteOrder") {
if (val == "Big" || val == "big")
throw GeographicErr("Only little-endian ordering is supported");
else if (!(val == "Little" || val == "little"))
throw GeographicErr("Unknown byte ordering " + val);
} else if (key == "ID")
_id = val;
// else unrecognized keywords are skipped
}
// Check values
if (!(isfinite(_a) && _a > 0))
throw GeographicErr("Reference radius must be positive");
if (!(_t0 > 0))
throw GeographicErr("Epoch time not defined");
if (_tmin >= _tmax)
throw GeographicErr("Min time exceeds max time");
if (_hmin >= _hmax)
throw GeographicErr("Min height exceeds max height");
if (int(_id.size()) != idlength_)
throw GeographicErr("Invalid ID");
if (_nNmodels < 1)
throw GeographicErr("NumModels must be positive");
if (!(_nNconstants == 0 || _nNconstants == 1))
throw GeographicErr("NumConstants must be 0 or 1");
if (!(_dt0 > 0)) {
if (_nNmodels > 1)
throw GeographicErr("DeltaEpoch must be positive");
else
_dt0 = 1;
}
}
void MagneticModel::FieldGeocentric(real t, real X, real Y, real Z,
real& BX, real& BY, real& BZ,
real& BXt, real& BYt, real& BZt) const {
t -= _t0;
int n = max(min(int(floor(t / _dt0)), _nNmodels - 1), 0);
bool interpolate = n + 1 < _nNmodels;
t -= n * _dt0;
// Components in geocentric basis
// initial values to suppress warning
real BXc = 0, BYc = 0, BZc = 0;
_harm[n](X, Y, Z, BX, BY, BZ);
_harm[n + 1](X, Y, Z, BXt, BYt, BZt);
if (_nNconstants)
_harm[_nNmodels + 1](X, Y, Z, BXc, BYc, BZc);
if (interpolate) {
// Convert to a time derivative
BXt = (BXt - BX) / _dt0;
BYt = (BYt - BY) / _dt0;
BZt = (BZt - BZ) / _dt0;
}
BX += t * BXt + BXc;
BY += t * BYt + BYc;
BZ += t * BZt + BZc;
BXt = BXt * - _a;
BYt = BYt * - _a;
BZt = BZt * - _a;
BX *= - _a;
BY *= - _a;
BZ *= - _a;
}
void MagneticModel::Field(real t, real lat, real lon, real h, bool diffp,
real& Bx, real& By, real& Bz,
real& Bxt, real& Byt, real& Bzt) const {
real X, Y, Z;
real M[Geocentric::dim2_];
_earth.IntForward(lat, lon, h, X, Y, Z, M);
// Components in geocentric basis
// initial values to suppress warning
real BX = 0, BY = 0, BZ = 0, BXt = 0, BYt = 0, BZt = 0;
FieldGeocentric(t, X, Y, Z, BX, BY, BZ, BXt, BYt, BZt);
if (diffp)
Geocentric::Unrotate(M, BXt, BYt, BZt, Bxt, Byt, Bzt);
Geocentric::Unrotate(M, BX, BY, BZ, Bx, By, Bz);
}
MagneticCircle MagneticModel::Circle(real t, real lat, real h) const {
real t1 = t - _t0;
int n = max(min(int(floor(t1 / _dt0)), _nNmodels - 1), 0);
bool interpolate = n + 1 < _nNmodels;
t1 -= n * _dt0;
real X, Y, Z, M[Geocentric::dim2_];
_earth.IntForward(lat, 0, h, X, Y, Z, M);
// Y = 0, cphi = M[7], sphi = M[8];
return (_nNconstants == 0 ?
MagneticCircle(_a, _earth._f, lat, h, t,
M[7], M[8], t1, _dt0, interpolate,
_harm[n].Circle(X, Z, true),
_harm[n + 1].Circle(X, Z, true)) :
MagneticCircle(_a, _earth._f, lat, h, t,
M[7], M[8], t1, _dt0, interpolate,
_harm[n].Circle(X, Z, true),
_harm[n + 1].Circle(X, Z, true),
_harm[_nNmodels + 1].Circle(X, Z, true)));
}
void 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) {
H = hypot(Bx, By);
Ht = H != 0 ? (Bx * Bxt + By * Byt) / H : hypot(Bxt, Byt);
D = H != 0 ? Math::atan2d(Bx, By) : Math::atan2d(Bxt, Byt);
Dt = (H != 0 ? (By * Bxt - Bx * Byt) / Math::sq(H) : 0) / Math::degree();
F = hypot(H, Bz);
Ft = F != 0 ? (H * Ht + Bz * Bzt) / F : hypot(Ht, Bzt);
I = F != 0 ? Math::atan2d(-Bz, H) : Math::atan2d(-Bzt, Ht);
It = (F != 0 ? (Bz * Ht - H * Bzt) / Math::sq(F) : 0) / Math::degree();
}
string MagneticModel::DefaultMagneticPath() {
string path;
char* magneticpath = getenv("GEOGRAPHICLIB_MAGNETIC_PATH");
if (magneticpath)
path = string(magneticpath);
if (!path.empty())
return path;
char* datapath = getenv("GEOGRAPHICLIB_DATA");
if (datapath)
path = string(datapath);
return (!path.empty() ? path : string(GEOGRAPHICLIB_DATA)) + "/magnetic";
}
string MagneticModel::DefaultMagneticName() {
string name;
char* magneticname = getenv("GEOGRAPHICLIB_MAGNETIC_NAME");
if (magneticname)
name = string(magneticname);
return !name.empty() ? name : string(GEOGRAPHICLIB_MAGNETIC_DEFAULT_NAME);
}
} // namespace GeographicLib
real
GeographicLib::Math::real real
Definition: GeodSolve.cpp:29
MagneticCircle.hpp
Header for GeographicLib::MagneticCircle class.
GEOGRAPHICLIB_DATA
#define GEOGRAPHICLIB_DATA
Definition: MagneticModel.cpp:20
GEOGRAPHICLIB_MAGNETIC_DEFAULT_NAME
#define GEOGRAPHICLIB_MAGNETIC_DEFAULT_NAME
Definition: MagneticModel.cpp:25
MagneticModel.hpp
Header for GeographicLib::MagneticModel class.
SphericalEngine.hpp
Header for GeographicLib::SphericalEngine class.
Utility.hpp
Header for GeographicLib::Utility class.
GeographicLib::Geocentric
Geocentric coordinates
Definition: Geocentric.hpp:67
GeographicLib::GeographicErr
Exception handling for GeographicLib.
Definition: Constants.hpp:316
GeographicLib::MagneticCircle
Geomagnetic field on a circle of latitude.
Definition: MagneticCircle.hpp:37
GeographicLib::MagneticModel::FieldGeocentric
void FieldGeocentric(real t, real X, real Y, real Z, real &BX, real &BY, real &BZ, real &BXt, real &BYt, real &BZt) const
Definition: MagneticModel.cpp:185
GeographicLib::MagneticModel::Circle
MagneticCircle Circle(real t, real lat, real h) const
Definition: MagneticModel.cpp:233
GeographicLib::MagneticModel::DefaultMagneticPath
static std::string DefaultMagneticPath()
Definition: MagneticModel.cpp:269
GeographicLib::MagneticModel::DefaultMagneticName
static std::string DefaultMagneticName()
Definition: MagneticModel.cpp:282
GeographicLib::MagneticModel::FieldComponents
static void FieldComponents(real Bx, real By, real Bz, real &H, real &F, real &D, real &I)
Definition: MagneticModel.hpp:249
GeographicLib::Math
Mathematical functions needed by GeographicLib.
Definition: Math.hpp:77
GeographicLib::Math::degree
static T degree()
Definition: Math.hpp:193
GeographicLib::Math::atan2d
static T atan2d(T y, T x)
Definition: Math.cpp:183
GeographicLib::Math::sq
static T sq(T x)
Definition: Math.hpp:205
GeographicLib::SphericalEngine::coeff::readcoeffs
static void readcoeffs(std::istream &stream, int &N, int &M, std::vector< real > &C, std::vector< real > &S, bool truncate=false)
Definition: SphericalEngine.cpp:385
GeographicLib::SphericalHarmonic
Spherical harmonic series.
Definition: SphericalHarmonic.hpp:71
GeographicLib::SphericalHarmonic::SCHMIDT
@ SCHMIDT
Definition: SphericalHarmonic.hpp:120
GeographicLib::SphericalHarmonic::FULL
@ FULL
Definition: SphericalHarmonic.hpp:98
GeographicLib::Utility::ParseLine
static bool ParseLine(const std::string &line, std::string &key, std::string &value, char equals='\0', char comment='#')
Definition: Utility.cpp:170
GeographicLib
Namespace for GeographicLib.
Definition: Accumulator.cpp:12
std
Definition: NearestNeighbor.hpp:812