GeographicLib  2.0
GravityCircle.hpp
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1 /**
2  * \file GravityCircle.hpp
3  * \brief Header for GeographicLib::GravityCircle class
4  *
5  * Copyright (c) Charles Karney (2011-2022) <charles@karney.com> and licensed
6  * under the MIT/X11 License. For more information, see
7  * https://geographiclib.sourceforge.io/
8  **********************************************************************/
9 
10 #if !defined(GEOGRAPHICLIB_GRAVITYCIRCLE_HPP)
11 #define GEOGRAPHICLIB_GRAVITYCIRCLE_HPP 1
12 
13 #include <vector>
17 
18 namespace GeographicLib {
19 
20  /**
21  * \brief Gravity on a circle of latitude
22  *
23  * Evaluate the earth's gravity field on a circle of constant height and
24  * latitude. This uses a CircularEngine to pre-evaluate the inner sum of the
25  * spherical harmonic sum, allowing the values of the field at several
26  * different longitudes to be evaluated rapidly.
27  *
28  * Use GravityModel::Circle to create a GravityCircle object. (The
29  * constructor for this class is private.)
30  *
31  * See \ref gravityparallel for an example of using GravityCircle (together
32  * with OpenMP) to speed up the computation of geoid heights.
33  *
34  * Example of use:
35  * \include example-GravityCircle.cpp
36  *
37  * <a href="Gravity.1.html">Gravity</a> is a command-line utility providing
38  * access to the functionality of GravityModel and GravityCircle.
39  **********************************************************************/
40 
42  private:
43  typedef Math::real real;
44  enum mask {
45  NONE = GravityModel::NONE,
46  GRAVITY = GravityModel::GRAVITY,
47  DISTURBANCE = GravityModel::DISTURBANCE,
48  DISTURBING_POTENTIAL = GravityModel::DISTURBING_POTENTIAL,
49  GEOID_HEIGHT = GravityModel::GEOID_HEIGHT,
50  SPHERICAL_ANOMALY = GravityModel::SPHERICAL_ANOMALY,
51  ALL = GravityModel::ALL,
52  };
53 
54  unsigned _caps;
55  real _a, _f, _lat, _h, _zZ, _pPx, _invR, _cpsi, _spsi,
56  _cphi, _sphi, _amodel, _gGMmodel, _dzonal0,
57  _corrmult, _gamma0, _gamma, _frot;
58  CircularEngine _gravitational, _disturbing, _correction;
59 
60  GravityCircle(mask caps, real a, real f, real lat, real h,
61  real Z, real P, real cphi, real sphi,
62  real amodel, real GMmodel,
63  real dzonal0, real corrmult,
64  real gamma0, real gamma, real frot,
65  const CircularEngine& gravitational,
66  const CircularEngine& disturbing,
67  const CircularEngine& correction);
68 
69  friend class GravityModel; // GravityModel calls the private constructor
70  Math::real W(real slam, real clam,
71  real& gX, real& gY, real& gZ) const;
72  Math::real V(real slam, real clam,
73  real& gX, real& gY, real& gZ) const;
74  Math::real InternalT(real slam, real clam,
75  real& deltaX, real& deltaY, real& deltaZ,
76  bool gradp, bool correct) const;
77  public:
78  /**
79  * A default constructor for the normal gravity. This sets up an
80  * uninitialized object which can be later replaced by the
81  * GravityModel::Circle.
82  **********************************************************************/
83  GravityCircle() : _a(-1) {}
84 
85  /** \name Compute the gravitational field
86  **********************************************************************/
87  ///@{
88  /**
89  * Evaluate the gravity.
90  *
91  * @param[in] lon the geographic longitude (degrees).
92  * @param[out] gx the easterly component of the acceleration
93  * (m s<sup>&minus;2</sup>).
94  * @param[out] gy the northerly component of the acceleration
95  * (m s<sup>&minus;2</sup>).
96  * @param[out] gz the upward component of the acceleration
97  * (m s<sup>&minus;2</sup>); this is usually negative.
98  * @return \e W the sum of the gravitational and centrifugal potentials
99  * (m<sup>2</sup> s<sup>&minus;2</sup>).
100  *
101  * The function includes the effects of the earth's rotation.
102  **********************************************************************/
103  Math::real Gravity(real lon, real& gx, real& gy, real& gz) const;
104 
105  /**
106  * Evaluate the gravity disturbance vector.
107  *
108  * @param[in] lon the geographic longitude (degrees).
109  * @param[out] deltax the easterly component of the disturbance vector
110  * (m s<sup>&minus;2</sup>).
111  * @param[out] deltay the northerly component of the disturbance vector
112  * (m s<sup>&minus;2</sup>).
113  * @param[out] deltaz the upward component of the disturbance vector
114  * (m s<sup>&minus;2</sup>).
115  * @return \e T the corresponding disturbing potential
116  * (m<sup>2</sup> s<sup>&minus;2</sup>).
117  **********************************************************************/
118  Math::real Disturbance(real lon, real& deltax, real& deltay, real& deltaz)
119  const;
120 
121  /**
122  * Evaluate the geoid height.
123  *
124  * @param[in] lon the geographic longitude (degrees).
125  * @return \e N the height of the geoid above the reference ellipsoid
126  * (meters).
127  *
128  * Some approximations are made in computing the geoid height so that the
129  * results of the NGA codes are reproduced accurately. Details are given
130  * in \ref gravitygeoid.
131  **********************************************************************/
132  Math::real GeoidHeight(real lon) const;
133 
134  /**
135  * Evaluate the components of the gravity anomaly vector using the
136  * spherical approximation.
137  *
138  * @param[in] lon the geographic longitude (degrees).
139  * @param[out] Dg01 the gravity anomaly (m s<sup>&minus;2</sup>).
140  * @param[out] xi the northerly component of the deflection of the vertical
141  * (degrees).
142  * @param[out] eta the easterly component of the deflection of the vertical
143  * (degrees).
144  *
145  * The spherical approximation (see Heiskanen and Moritz, Sec 2-14) is used
146  * so that the results of the NGA codes are reproduced accurately.
147  * approximations used here. Details are given in \ref gravitygeoid.
148  **********************************************************************/
149  void SphericalAnomaly(real lon, real& Dg01, real& xi, real& eta)
150  const;
151 
152  /**
153  * Evaluate the components of the acceleration due to gravity and the
154  * centrifugal acceleration in geocentric coordinates.
155  *
156  * @param[in] lon the geographic longitude (degrees).
157  * @param[out] gX the \e X component of the acceleration
158  * (m s<sup>&minus;2</sup>).
159  * @param[out] gY the \e Y component of the acceleration
160  * (m s<sup>&minus;2</sup>).
161  * @param[out] gZ the \e Z component of the acceleration
162  * (m s<sup>&minus;2</sup>).
163  * @return \e W = \e V + &Phi; the sum of the gravitational and
164  * centrifugal potentials (m<sup>2</sup> s<sup>&minus;2</sup>).
165  **********************************************************************/
166  Math::real W(real lon, real& gX, real& gY, real& gZ) const {
167  real slam, clam;
168  Math::sincosd(lon, slam, clam);
169  return W(slam, clam, gX, gY, gZ);
170  }
171 
172  /**
173  * Evaluate the components of the acceleration due to gravity in geocentric
174  * coordinates.
175  *
176  * @param[in] lon the geographic longitude (degrees).
177  * @param[out] GX the \e X component of the acceleration
178  * (m s<sup>&minus;2</sup>).
179  * @param[out] GY the \e Y component of the acceleration
180  * (m s<sup>&minus;2</sup>).
181  * @param[out] GZ the \e Z component of the acceleration
182  * (m s<sup>&minus;2</sup>).
183  * @return \e V = \e W - &Phi; the gravitational potential
184  * (m<sup>2</sup> s<sup>&minus;2</sup>).
185  **********************************************************************/
186  Math::real V(real lon, real& GX, real& GY, real& GZ) const {
187  real slam, clam;
188  Math::sincosd(lon, slam, clam);
189  return V(slam, clam, GX, GY, GZ);
190  }
191 
192  /**
193  * Evaluate the components of the gravity disturbance in geocentric
194  * coordinates.
195  *
196  * @param[in] lon the geographic longitude (degrees).
197  * @param[out] deltaX the \e X component of the gravity disturbance
198  * (m s<sup>&minus;2</sup>).
199  * @param[out] deltaY the \e Y component of the gravity disturbance
200  * (m s<sup>&minus;2</sup>).
201  * @param[out] deltaZ the \e Z component of the gravity disturbance
202  * (m s<sup>&minus;2</sup>).
203  * @return \e T = \e W - \e U the disturbing potential (also called the
204  * anomalous potential) (m<sup>2</sup> s<sup>&minus;2</sup>).
205  **********************************************************************/
206  Math::real T(real lon, real& deltaX, real& deltaY, real& deltaZ)
207  const {
208  real slam, clam;
209  Math::sincosd(lon, slam, clam);
210  return InternalT(slam, clam, deltaX, deltaY, deltaZ, true, true);
211  }
212 
213  /**
214  * Evaluate disturbing potential in geocentric coordinates.
215  *
216  * @param[in] lon the geographic longitude (degrees).
217  * @return \e T = \e W - \e U the disturbing potential (also called the
218  * anomalous potential) (m<sup>2</sup> s<sup>&minus;2</sup>).
219  **********************************************************************/
220  Math::real T(real lon) const {
221  real slam, clam, dummy;
222  Math::sincosd(lon, slam, clam);
223  return InternalT(slam, clam, dummy, dummy, dummy, false, true);
224  }
225 
226  ///@}
227 
228  /** \name Inspector functions
229  **********************************************************************/
230  ///@{
231  /**
232  * @return true if the object has been initialized.
233  **********************************************************************/
234  bool Init() const { return _a > 0; }
235 
236  /**
237  * @return \e a the equatorial radius of the ellipsoid (meters). This is
238  * the value inherited from the GravityModel object used in the
239  * constructor.
240  **********************************************************************/
242  { return Init() ? _a : Math::NaN(); }
243 
244  /**
245  * @return \e f the flattening of the ellipsoid. This is the value
246  * inherited from the GravityModel object used in the constructor.
247  **********************************************************************/
249  { return Init() ? _f : Math::NaN(); }
250 
251  /**
252  * @return the latitude of the circle (degrees).
253  **********************************************************************/
255  { return Init() ? _lat : Math::NaN(); }
256 
257  /**
258  * @return the height of the circle (meters).
259  **********************************************************************/
261  { return Init() ? _h : Math::NaN(); }
262 
263  /**
264  * @return \e caps the computational capabilities that this object was
265  * constructed with.
266  **********************************************************************/
267  unsigned Capabilities() const { return _caps; }
268 
269  /**
270  * @param[in] testcaps a set of bitor'ed GravityModel::mask values.
271  * @return true if the GravityCircle object has all these capabilities.
272  **********************************************************************/
273  bool Capabilities(unsigned testcaps) const {
274  return (_caps & testcaps) == testcaps;
275  }
276  ///@}
277  };
278 
279 } // namespace GeographicLib
280 
281 #endif // GEOGRAPHICLIB_GRAVITYCIRCLE_HPP
Header for GeographicLib::CircularEngine class.
Header for GeographicLib::Constants class.
#define GEOGRAPHICLIB_EXPORT
Definition: Constants.hpp:67
GeographicLib::Math::real real
Definition: GeodSolve.cpp:31
Header for GeographicLib::GravityModel class.
Spherical harmonic sums for a circle.
Gravity on a circle of latitude.
Math::real EquatorialRadius() const
Math::real V(real lon, real &GX, real &GY, real &GZ) const
Math::real W(real lon, real &gX, real &gY, real &gZ) const
Math::real Flattening() const
Math::real T(real lon, real &deltaX, real &deltaY, real &deltaZ) const
bool Capabilities(unsigned testcaps) const
Math::real T(real lon) const
Model of the earth's gravity field.
static void sincosd(T x, T &sinx, T &cosx)
Definition: Math.cpp:106
static T NaN()
Definition: Math.cpp:250
Namespace for GeographicLib.
Definition: Accumulator.cpp:12