GeographicLib: GravityModel.cpp Source File

GeographicLib 2.7

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GravityModel.cpp
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1/**
2 * \file GravityModel.cpp
3 * \brief Implementation for GeographicLib::GravityModel class
4 *
5 * Copyright (c) Charles Karney (2011-2023) <karney@alum.mit.edu> and licensed
6 * under the MIT/X11 License. For more information, see
7 * https://geographiclib.sourceforge.io/
8 **********************************************************************/
9
10#include <GeographicLib/GravityModel.hpp>
11#include <fstream>
12#include <limits>
13#include <GeographicLib/SphericalEngine.hpp>
14#include <GeographicLib/GravityCircle.hpp>
15#include <GeographicLib/Utility.hpp>
16
17#if !defined(GEOGRAPHICLIB_DATA)
18# if defined(_WIN32)
19# define GEOGRAPHICLIB_DATA "C:/ProgramData/GeographicLib"
20# else
21# define GEOGRAPHICLIB_DATA "/usr/local/share/GeographicLib"
22# endif
23#endif
24
25#if !defined(GEOGRAPHICLIB_GRAVITY_DEFAULT_NAME)
26# define GEOGRAPHICLIB_GRAVITY_DEFAULT_NAME "egm96"
27#endif
28
29#if defined(_MSC_VER)
30// Squelch warnings about unsafe use of getenv
31# pragma warning (disable: 4996)
32#endif
33
34namespace GeographicLib {
35
36 using namespace std;
37
38 GravityModel::GravityModel(const std::string& name, const std::string& path,
39 int Nmax, int Mmax)
40 : _name(name)
41 , _dir(path)
42 , _description("NONE")
43 , _date("UNKNOWN")
44 , _amodel(Math::NaN())
45 , _gGMmodel(Math::NaN())
46 , _zeta0(0)
47 , _corrmult(1)
48 , _nmx(-1)
49 , _mmx(-1)
50 , _norm(SphericalHarmonic::FULL)
51 {
52 if (_dir.empty())
53 _dir = DefaultGravityPath();
54 bool truncate = Nmax >= 0 || Mmax >= 0;
55 if (truncate) {
56 if (Nmax >= 0 && Mmax < 0) Mmax = Nmax;
57 if (Nmax < 0) Nmax = numeric_limits<int>::max();
58 if (Mmax < 0) Mmax = numeric_limits<int>::max();
59 }
60 ReadMetadata(_name);
61 {
62 string coeff = _filename + ".cof";
63 ifstream coeffstr(coeff.c_str(), ios::binary);
64 if (!coeffstr.good())
65 throw GeographicErr("Error opening " + coeff);
66 char id[idlength_ + 1];
67 coeffstr.read(id, idlength_);
68 if (!coeffstr.good())
69 throw GeographicErr("No header in " + coeff);
70 id[idlength_] = '\0';
71 if (_id != string(id))
72 throw GeographicErr("ID mismatch: " + _id + " vs " + id);
73 int N, M;
74 if (truncate) { N = Nmax; M = Mmax; }
75 SphericalEngine::coeff::readcoeffs(coeffstr, N, M, _cCx, _sSx, truncate);
76 if (!(N >= 0 && M >= 0))
77 throw GeographicErr("Degree and order must be at least 0");
78 if (_cCx[0] != 0)
79 throw GeographicErr("The degree 0 term should be zero");
80 _cCx[0] = 1; // Include the 1/r term in the sum
81 _gravitational = SphericalHarmonic(_cCx, _sSx, N, N, M, _amodel, _norm);
82 if (truncate) { N = Nmax; M = Mmax; }
83 SphericalEngine::coeff::readcoeffs(coeffstr, N, M, _cCC, _cCS, truncate);
84 if (N < 0) {
85 N = M = 0;
86 _cCC.resize(1, real(0));
87 }
88 _cCC[0] += _zeta0 / _corrmult;
89 _correction = SphericalHarmonic(_cCC, _cCS, N, N, M, real(1), _norm);
90 int pos = int(coeffstr.tellg());
91 coeffstr.seekg(0, ios::end);
92 if (pos != coeffstr.tellg())
93 throw GeographicErr("Extra data in " + coeff);
94 }
95 int nmx = _gravitational.Coefficients().nmx();
96 _nmx = max(nmx, _correction.Coefficients().nmx());
97 _mmx = max(_gravitational.Coefficients().mmx(),
98 _correction.Coefficients().mmx());
99 // Adjust the normalization of the normal potential to match the model.
100 real mult = _earth._gGM / _gGMmodel;
101 real amult = Math::sq(_earth._a / _amodel);
102 // The 0th term in _zonal should be is 1 + _dzonal0. Instead set it to 1
103 // to give exact cancellation with the (0,0) term in the model and account
104 // for _dzonal0 separately.
105 _zonal.clear(); _zonal.push_back(1);
106 _dzonal0 = (_earth.MassConstant() - _gGMmodel) / _gGMmodel;
107 for (int n = 2; n <= nmx; n += 2) {
108 // Only include as many normal zonal terms as matter. Figuring the limit
109 // in this way works because the coefficients of the normal potential
110 // (which is smooth) decay much more rapidly that the corresponding
111 // coefficient of the model potential (which is bumpy). Typically this
112 // goes out to n = 18.
113 mult *= amult;
114 real
115 r = _cCx[n], // the model term
116 s = - mult * _earth.Jn(n) / sqrt(real(2 * n + 1)), // the normal term
117 t = r - s; // the difference
118 if (t == r) // the normal term is negligible
119 break;
120 _zonal.push_back(0); // index = n - 1; the odd terms are 0
121 _zonal.push_back(s);
122 }
123 int nmx1 = int(_zonal.size()) - 1;
124 _disturbing = SphericalHarmonic1(_cCx, _sSx,
125 _gravitational.Coefficients().N(),
126 nmx, _gravitational.Coefficients().mmx(),
127 _zonal,
128 _zonal, // This is not accessed!
129 nmx1, nmx1, 0,
130 _amodel,
131 SphericalHarmonic1::normalization(_norm));
132 }
133
134 void GravityModel::ReadMetadata(const string& name) {
135 const char* spaces = " \t\n\v\f\r";
136 _filename = _dir + "/" + name + ".egm";
137 ifstream metastr(_filename.c_str());
138 if (!metastr.good())
139 throw GeographicErr("Cannot open " + _filename);
140 string line;
141 getline(metastr, line);
142 if (!(line.size() >= 6 && line.substr(0,5) == "EGMF-"))
143 throw GeographicErr(_filename + " does not contain EGMF-n signature");
144 string::size_type n = line.find_first_of(spaces, 5);
145 if (n != string::npos)
146 n -= 5;
147 string version(line, 5, n);
148 if (version != "1")
149 throw GeographicErr("Unknown version in " + _filename + ": " + version);
150 string key, val;
151 real a = Math::NaN(), GM = a, omega = a, f = a, J2 = a;
152 while (getline(metastr, line)) {
153 if (!Utility::ParseLine(line, key, val))
154 continue;
155 // Process key words
156 if (key == "Name")
157 _name = val;
158 else if (key == "Description")
159 _description = val;
160 else if (key == "ReleaseDate")
161 _date = val;
162 else if (key == "ModelRadius")
163 _amodel = Utility::val<real>(val);
164 else if (key == "ModelMass")
165 _gGMmodel = Utility::val<real>(val);
166 else if (key == "AngularVelocity")
167 omega = Utility::val<real>(val);
168 else if (key == "ReferenceRadius")
169 a = Utility::val<real>(val);
170 else if (key == "ReferenceMass")
171 GM = Utility::val<real>(val);
172 else if (key == "Flattening")
173 f = Utility::fract<real>(val);
174 else if (key == "DynamicalFormFactor")
175 J2 = Utility::fract<real>(val);
176 else if (key == "HeightOffset")
177 _zeta0 = Utility::fract<real>(val);
178 else if (key == "CorrectionMultiplier")
179 _corrmult = Utility::fract<real>(val);
180 else if (key == "Normalization") {
181 if (val == "FULL" || val == "Full" || val == "full")
182 _norm = SphericalHarmonic::FULL;
183 else if (val == "SCHMIDT" || val == "Schmidt" || val == "schmidt")
184 _norm = SphericalHarmonic::SCHMIDT;
185 else
186 throw GeographicErr("Unknown normalization " + val);
187 } else if (key == "ByteOrder") {
188 if (val == "Big" || val == "big")
189 throw GeographicErr("Only little-endian ordering is supported");
190 else if (!(val == "Little" || val == "little"))
191 throw GeographicErr("Unknown byte ordering " + val);
192 } else if (key == "ID")
193 _id = val;
194 // else unrecognized keywords are skipped
195 }
196 // Check values
197 if (!(isfinite(_amodel) && _amodel > 0))
198 throw GeographicErr("Model radius must be positive");
199 if (!(isfinite(_gGMmodel) && _gGMmodel > 0))
200 throw GeographicErr("Model mass constant must be positive");
201 if (!(isfinite(_corrmult) && _corrmult > 0))
202 throw GeographicErr("Correction multiplier must be positive");
203 if (!(isfinite(_zeta0)))
204 throw GeographicErr("Height offset must be finite");
205 if (int(_id.size()) != idlength_)
206 throw GeographicErr("Invalid ID");
207 if (isfinite(f) && isfinite(J2))
208 throw GeographicErr("Cannot specify both f and J2");
209 _earth = NormalGravity(a, GM, omega,
210 isfinite(f) ? f : J2, isfinite(f));
211 }
212
213 Math::real GravityModel::InternalT(real X, real Y, real Z,
214 real& deltaX, real& deltaY, real& deltaZ,
215 bool gradp, bool correct) const {
216 // If correct, then produce the correct T = W - U. Otherwise, neglect the
217 // n = 0 term (which is proportial to the difference in the model and
218 // reference values of GM).
219 if (_dzonal0 == 0)
220 // No need to do the correction
221 correct = false;
222 real T, invR = correct ? 1 / hypot(hypot(X, Y), Z) : 1;
223 if (gradp) {
224 // initial values to suppress warnings
225 deltaX = deltaY = deltaZ = 0;
226 T = _disturbing(-1, X, Y, Z, deltaX, deltaY, deltaZ);
227 real f = _gGMmodel / _amodel;
228 deltaX *= f;
229 deltaY *= f;
230 deltaZ *= f;
231 if (correct) {
232 invR = _gGMmodel * _dzonal0 * invR * invR * invR;
233 deltaX += X * invR;
234 deltaY += Y * invR;
235 deltaZ += Z * invR;
236 }
237 } else
238 T = _disturbing(-1, X, Y, Z);
239 T = (T / _amodel - (correct ? _dzonal0 : 0) * invR) * _gGMmodel;
240 return T;
241 }
242
243 Math::real GravityModel::V(real X, real Y, real Z,
244 real& GX, real& GY, real& GZ) const {
245 real
246 Vres = _gravitational(X, Y, Z, GX, GY, GZ),
247 f = _gGMmodel / _amodel;
248 Vres *= f;
249 GX *= f;
250 GY *= f;
251 GZ *= f;
252 return Vres;
253 }
254
255 Math::real GravityModel::W(real X, real Y, real Z,
256 real& gX, real& gY, real& gZ) const {
257 real fX, fY,
258 Wres = V(X, Y, Z, gX, gY, gZ) + _earth.Phi(X, Y, fX, fY);
259 gX += fX;
260 gY += fY;
261 return Wres;
262 }
263
264 void GravityModel::SphericalAnomaly(real lat, real lon, real h,
265 real& Dg01, real& xi, real& eta) const {
266 real X, Y, Z, M[Geocentric::dim2_];
267 _earth.Earth().IntForward(lat, lon, h, X, Y, Z, M);
268 real
269 deltax, deltay, deltaz,
270 T = InternalT(X, Y, Z, deltax, deltay, deltaz, true, false),
271 clam = M[3], slam = -M[0],
272 P = hypot(X, Y),
273 R = hypot(P, Z),
274 // theta is geocentric latitude
275 ctheta = R != 0 ? P / R : M[7],
276 stheta = R != 0 ? Z / R : M[8];
277 // Rotate cartesian into spherical coordinates
278 real MC[Geocentric::dim2_];
279 Geocentric::Rotation(stheta, ctheta, slam, clam, MC);
280 Geocentric::Unrotate(MC, deltax, deltay, deltaz, deltax, deltay, deltaz);
281 // H+M, Eq 2-151c
282 Dg01 = - deltaz - 2 * T / R;
283 real gammaX, gammaY, gammaZ;
284 _earth.U(X, Y, Z, gammaX, gammaY, gammaZ);
285 real gamma = hypot( hypot(gammaX, gammaY), gammaZ);
286 xi = -(deltay/gamma) / Math::degree();
287 eta = -(deltax/gamma) / Math::degree();
288 }
289
290 Math::real GravityModel::GeoidHeight(real lat, real lon) const
291 {
292 real X, Y, Z;
293 _earth.Earth().IntForward(lat, lon, 0, X, Y, Z, NULL);
294 real
295 gamma0 = _earth.SurfaceGravity(lat),
296 dummy,
297 T = InternalT(X, Y, Z, dummy, dummy, dummy, false, false),
298 invR = 1 / hypot(hypot(X, Y), Z),
299 correction = _corrmult * _correction(invR * X, invR * Y, invR * Z);
300 // _zeta0 has been included in _correction
301 return T/gamma0 + correction;
302 }
303
304 Math::real GravityModel::Gravity(real lat, real lon, real h,
305 real& gx, real& gy, real& gz) const {
306 real X, Y, Z, M[Geocentric::dim2_];
307 _earth.Earth().IntForward(lat, lon, h, X, Y, Z, M);
308 real Wres = W(X, Y, Z, gx, gy, gz);
309 Geocentric::Unrotate(M, gx, gy, gz, gx, gy, gz);
310 return Wres;
311 }
312 Math::real GravityModel::Disturbance(real lat, real lon, real h,
313 real& deltax, real& deltay,
314 real& deltaz) const {
315 real X, Y, Z, M[Geocentric::dim2_];
316 _earth.Earth().IntForward(lat, lon, h, X, Y, Z, M);
317 real Tres = InternalT(X, Y, Z, deltax, deltay, deltaz, true, true);
318 Geocentric::Unrotate(M, deltax, deltay, deltaz, deltax, deltay, deltaz);
319 return Tres;
320 }
321
322 GravityCircle GravityModel::Circle(real lat, real h, unsigned caps) const {
323 if (h != 0)
324 // Disallow invoking GeoidHeight unless h is zero.
325 caps &= ~(CAP_GAMMA0 | CAP_C);
326 real X, Y, Z, M[Geocentric::dim2_];
327 _earth.Earth().IntForward(lat, 0, h, X, Y, Z, M);
328 // Y = 0, cphi = M[7], sphi = M[8];
329 real
330 invR = 1 / hypot(X, Z),
331 gamma0 = (caps & CAP_GAMMA0 ?_earth.SurfaceGravity(lat)
332 : Math::NaN()),
333 fx, fy, fz, gamma;
334 if (caps & CAP_GAMMA) {
335 _earth.U(X, Y, Z, fx, fy, fz); // fy = 0
336 gamma = hypot(fx, fz);
337 } else
338 gamma = Math::NaN();
339 _earth.Phi(X, Y, fx, fy);
340 return GravityCircle(GravityCircle::mask(caps),
341 _earth._a, _earth._f, lat, h, Z, X, M[7], M[8],
342 _amodel, _gGMmodel, _dzonal0, _corrmult,
343 gamma0, gamma, fx,
344 caps & CAP_G ?
345 _gravitational.Circle(X, Z, true) :
346 CircularEngine(),
347 // N.B. If CAP_DELTA is set then CAP_T should be too.
348 caps & CAP_T ?
349 _disturbing.Circle(-1, X, Z, (caps&CAP_DELTA) != 0) :
350 CircularEngine(),
351 caps & CAP_C ?
352 _correction.Circle(invR * X, invR * Z, false) :
353 CircularEngine());
354 }
355
356 string GravityModel::DefaultGravityPath() {
357 string path;
358 char* gravitypath = getenv("GEOGRAPHICLIB_GRAVITY_PATH");
359 if (gravitypath)
360 path = string(gravitypath);
361 if (!path.empty())
362 return path;
363 char* datapath = getenv("GEOGRAPHICLIB_DATA");
364 if (datapath)
365 path = string(datapath);
366 return (!path.empty() ? path : string(GEOGRAPHICLIB_DATA)) + "/gravity";
367 }
368
369 string GravityModel::DefaultGravityName() {
370 string name;
371 char* gravityname = getenv("GEOGRAPHICLIB_GRAVITY_NAME");
372 if (gravityname)
373 name = string(gravityname);
374 return !name.empty() ? name : string(GEOGRAPHICLIB_GRAVITY_DEFAULT_NAME);
375 }
376
377} // namespace GeographicLib
real
GeographicLib::Math::real real
Definition Geod3Solve.cpp:25
GEOGRAPHICLIB_DATA
#define GEOGRAPHICLIB_DATA
Definition Geoid.cpp:19
GravityCircle.hpp
Header for GeographicLib::GravityCircle class.
GEOGRAPHICLIB_GRAVITY_DEFAULT_NAME
#define GEOGRAPHICLIB_GRAVITY_DEFAULT_NAME
Definition GravityModel.cpp:26
GravityModel.hpp
Header for GeographicLib::GravityModel class.
SphericalEngine.hpp
Header for GeographicLib::SphericalEngine class.
Utility.hpp
Header for GeographicLib::Utility class.
GeographicLib::CircularEngine
Spherical harmonic sums for a circle.
Definition CircularEngine.hpp:52
GeographicLib::GeographicErr
Exception handling for GeographicLib.
Definition Constants.hpp:344
GeographicLib::GravityModel::GravityCircle
friend class GravityCircle
Definition GravityModel.hpp:86
GeographicLib::GravityModel::Disturbance
Math::real Disturbance(real lat, real lon, real h, real &deltax, real &deltay, real &deltaz) const
Definition GravityModel.cpp:312
GeographicLib::GravityModel::DefaultGravityPath
static std::string DefaultGravityPath()
Definition GravityModel.cpp:356
GeographicLib::GravityModel::SphericalAnomaly
void SphericalAnomaly(real lat, real lon, real h, real &Dg01, real &xi, real &eta) const
Definition GravityModel.cpp:264
GeographicLib::GravityModel::Circle
GravityCircle Circle(real lat, real h, unsigned caps=ALL) const
Definition GravityModel.cpp:322
GeographicLib::GravityModel::DefaultGravityName
static std::string DefaultGravityName()
Definition GravityModel.cpp:369
GeographicLib::GravityModel::GeoidHeight
Math::real GeoidHeight(real lat, real lon) const
Definition GravityModel.cpp:290
GeographicLib::GravityModel::T
Math::real T(real X, real Y, real Z, real &deltaX, real &deltaY, real &deltaZ) const
Definition GravityModel.hpp:348
GeographicLib::GravityModel::Gravity
Math::real Gravity(real lat, real lon, real h, real &gx, real &gy, real &gz) const
Definition GravityModel.cpp:304
GeographicLib::GravityModel::V
Math::real V(real X, real Y, real Z, real &GX, real &GY, real &GZ) const
Definition GravityModel.cpp:243
GeographicLib::GravityModel::W
Math::real W(real X, real Y, real Z, real &gX, real &gY, real &gZ) const
Definition GravityModel.cpp:255
GeographicLib::Math
Mathematical functions needed by GeographicLib.
Definition Math.hpp:82
GeographicLib::Math::degree
static T degree()
Definition Math.hpp:197
GeographicLib::Math::sq
static T sq(T x)
Definition Math.hpp:209
GeographicLib::Math::NaN
static T NaN()
Definition Math.cpp:301
GeographicLib::Math::real
double real
Definition Math.hpp:115
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:384
GeographicLib::SphericalHarmonic1
Spherical harmonic series with a correction to the coefficients.
Definition SphericalHarmonic1.hpp:32
GeographicLib::SphericalHarmonic1::normalization
normalization
Definition SphericalHarmonic1.hpp:37
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::Utility::fract
static T fract(const std::string &s)
Definition Utility.hpp:298
GeographicLib::Utility::val
static T val(const std::string &s)
Definition Utility.hpp:225
GeographicLib
Namespace for GeographicLib.
Definition Accumulator.cpp:12
std
Definition NearestNeighbor.hpp:806