GeographicLib: SphericalEngine.hpp Source File

GeographicLib 2.7

Loading...
Searching...
No Matches
SphericalEngine.hpp
Go to the documentation of this file.
1/**
2 * \file SphericalEngine.hpp
3 * \brief Header for GeographicLib::SphericalEngine class
4 *
5 * Copyright (c) Charles Karney (2011-2019) <karney@alum.mit.edu> and licensed
6 * under the MIT/X11 License. For more information, see
7 * https://geographiclib.sourceforge.io/
8 **********************************************************************/
9
10#if !defined(GEOGRAPHICLIB_SPHERICALENGINE_HPP)
11#define GEOGRAPHICLIB_SPHERICALENGINE_HPP 1
12
13#include <vector>
14#include <istream>
15#include <GeographicLib/Constants.hpp>
16
17#if defined(_MSC_VER)
18// Squelch warnings about dll vs vector
19# pragma warning (push)
20# pragma warning (disable: 4251)
21#endif
22
23namespace GeographicLib {
24
25 class CircularEngine;
26
27 /**
28 * \brief The evaluation engine for SphericalHarmonic
29 *
30 * This serves as the backend to SphericalHarmonic, SphericalHarmonic1, and
31 * SphericalHarmonic2. Typically end-users will not have to access this
32 * class directly.
33 *
34 * See SphericalEngine.cpp for more information on the implementation.
35 *
36 * Example of use:
37 * \include example-SphericalEngine.cpp
38 **********************************************************************/
39
40 class GEOGRAPHICLIB_EXPORT SphericalEngine {
41 private:
42 typedef Math::real real;
43 // CircularEngine needs access to sqrttable, scale
44 friend class CircularEngine;
45 // Return the table of the square roots of integers
46 static std::vector<real>& sqrttable();
47 // An internal scaling of the coefficients to avoid overflow in
48 // intermediate calculations.
49 static real scale() {
50 using std::pow;
51 static const real
52 // Need extra real because, since C++11, pow(float, int) returns double
53 s = real(pow(real(std::numeric_limits<real>::radix),
54 -3 * (std::numeric_limits<real>::max_exponent < (1<<14) ?
55 std::numeric_limits<real>::max_exponent : (1<<14))
56 / 5));
57 return s;
58 }
59 // Move latitudes near the pole off the axis by this amount.
60 static real eps() {
61 using std::sqrt;
62 return std::numeric_limits<real>::epsilon() *
63 sqrt(std::numeric_limits<real>::epsilon());
64 }
65 SphericalEngine(); // Disable constructor
66 public:
67 /**
68 * Supported normalizations for associated Legendre polynomials.
69 **********************************************************************/
70 enum normalization {
71 /**
72 * Fully normalized associated Legendre polynomials. See
73 * SphericalHarmonic::FULL for documentation.
74 *
75 * @hideinitializer
76 **********************************************************************/
77 FULL = 0,
78 /**
79 * Schmidt semi-normalized associated Legendre polynomials. See
80 * SphericalHarmonic::SCHMIDT for documentation.
81 *
82 * @hideinitializer
83 **********************************************************************/
84 SCHMIDT = 1,
85 };
86
87 /**
88 * \brief Package up coefficients for SphericalEngine
89 *
90 * This packages up the \e C, \e S coefficients and information about how
91 * the coefficients are stored into a single structure. This allows a
92 * vector of type SphericalEngine::coeff to be passed to
93 * SphericalEngine::Value. This class also includes functions to aid
94 * indexing into \e C and \e S.
95 *
96 * The storage layout of the coefficients is documented in
97 * SphericalHarmonic and SphericalHarmonic::SphericalHarmonic.
98 **********************************************************************/
99 class GEOGRAPHICLIB_EXPORT coeff {
100 private:
101 int _nNx, _nmx, _mmx;
102 std::vector<real>::const_iterator _cCnm;
103 std::vector<real>::const_iterator _sSnm;
104 public:
105 /**
106 * A default constructor
107 **********************************************************************/
108 coeff() : _nNx(-1) , _nmx(-1) , _mmx(-1) {}
109 /**
110 * The general constructor.
111 *
112 * @param[in] C a vector of coefficients for the cosine terms.
113 * @param[in] S a vector of coefficients for the sine terms.
114 * @param[in] N the degree giving storage layout for \e C and \e S.
115 * @param[in] nmx the maximum degree to be used.
116 * @param[in] mmx the maximum order to be used.
117 * @exception GeographicErr if \e N, \e nmx, and \e mmx do not satisfy
118 * \e N &ge; \e nmx &ge; \e mmx &ge; &minus;1.
119 * @exception GeographicErr if \e C or \e S is not big enough to hold the
120 * coefficients.
121 * @exception std::bad_alloc if the memory for the square root table
122 * can't be allocated.
123 **********************************************************************/
124 coeff(const std::vector<real>& C,
125 const std::vector<real>& S,
126 int N, int nmx, int mmx)
127 : _nNx(N)
128 , _nmx(nmx)
129 , _mmx(mmx)
130 , _cCnm(C.begin())
131 , _sSnm(S.begin())
132 {
133 if (!((_nNx >= _nmx && _nmx >= _mmx && _mmx >= 0) ||
134 // If mmx = -1 then the sums are empty so require nmx = -1 also.
135 (_nmx == -1 && _mmx == -1)))
136 throw GeographicErr("Bad indices for coeff");
137 if (!(index(_nmx, _mmx) < int(C.size()) &&
138 index(_nmx, _mmx) < int(S.size()) + (_nNx + 1)))
139 throw GeographicErr("Arrays too small in coeff");
140 SphericalEngine::RootTable(_nmx);
141 }
142 /**
143 * The constructor for full coefficient vectors.
144 *
145 * @param[in] C a vector of coefficients for the cosine terms.
146 * @param[in] S a vector of coefficients for the sine terms.
147 * @param[in] N the maximum degree and order.
148 * @exception GeographicErr if \e N does not satisfy \e N &ge; &minus;1.
149 * @exception GeographicErr if \e C or \e S is not big enough to hold the
150 * coefficients.
151 * @exception std::bad_alloc if the memory for the square root table
152 * can't be allocated.
153 **********************************************************************/
154 coeff(const std::vector<real>& C,
155 const std::vector<real>& S,
156 int N)
157 : _nNx(N)
158 , _nmx(N)
159 , _mmx(N)
160 , _cCnm(C.begin())
161 , _sSnm(S.begin())
162 {
163 if (!(_nNx >= -1))
164 throw GeographicErr("Bad indices for coeff");
165 if (!(index(_nmx, _mmx) < int(C.size()) &&
166 index(_nmx, _mmx) < int(S.size()) + (_nNx + 1)))
167 throw GeographicErr("Arrays too small in coeff");
168 SphericalEngine::RootTable(_nmx);
169 }
170 /**
171 * @return \e N the degree giving storage layout for \e C and \e S.
172 **********************************************************************/
173 int N() const { return _nNx; }
174 /**
175 * @return \e nmx the maximum degree to be used.
176 **********************************************************************/
177 int nmx() const { return _nmx; }
178 /**
179 * @return \e mmx the maximum order to be used.
180 **********************************************************************/
181 int mmx() const { return _mmx; }
182 /**
183 * The one-dimensional index into \e C and \e S.
184 *
185 * @param[in] n the degree.
186 * @param[in] m the order.
187 * @return the one-dimensional index.
188 **********************************************************************/
189 int index(int n, int m) const
190 { return m * _nNx - m * (m - 1) / 2 + n; }
191 /**
192 * An element of \e C.
193 *
194 * @param[in] k the one-dimensional index.
195 * @return the value of the \e C coefficient.
196 **********************************************************************/
197 Math::real Cv(int k) const { return *(_cCnm + k); }
198 /**
199 * An element of \e S.
200 *
201 * @param[in] k the one-dimensional index.
202 * @return the value of the \e S coefficient.
203 **********************************************************************/
204 Math::real Sv(int k) const { return *(_sSnm + (k - (_nNx + 1))); }
205 /**
206 * An element of \e C with checking.
207 *
208 * @param[in] k the one-dimensional index.
209 * @param[in] n the requested degree.
210 * @param[in] m the requested order.
211 * @param[in] f a multiplier.
212 * @return the value of the \e C coefficient multiplied by \e f in \e n
213 * and \e m are in range else 0.
214 **********************************************************************/
215 Math::real Cv(int k, int n, int m, real f) const
216 { return m > _mmx || n > _nmx ? 0 : *(_cCnm + k) * f; }
217 /**
218 * An element of \e S with checking.
219 *
220 * @param[in] k the one-dimensional index.
221 * @param[in] n the requested degree.
222 * @param[in] m the requested order.
223 * @param[in] f a multiplier.
224 * @return the value of the \e S coefficient multiplied by \e f in \e n
225 * and \e m are in range else 0.
226 **********************************************************************/
227 Math::real Sv(int k, int n, int m, real f) const
228 { return m > _mmx || n > _nmx ? 0 : *(_sSnm + (k - (_nNx + 1))) * f; }
229
230 /**
231 * The size of the coefficient vector for the cosine terms.
232 *
233 * @param[in] N the maximum degree.
234 * @param[in] M the maximum order.
235 * @return the size of the vector of cosine terms as stored in column
236 * major order.
237 **********************************************************************/
238 static int Csize(int N, int M)
239 { return (M + 1) * (2 * N - M + 2) / 2; }
240
241 /**
242 * The size of the coefficient vector for the sine terms.
243 *
244 * @param[in] N the maximum degree.
245 * @param[in] M the maximum order.
246 * @return the size of the vector of cosine terms as stored in column
247 * major order.
248 **********************************************************************/
249 static int Ssize(int N, int M)
250 { return Csize(N, M) - (N + 1); }
251
252 /**
253 * Load coefficients from a binary stream.
254 *
255 * @param[in] stream the input stream.
256 * @param[in,out] N The maximum degree of the coefficients.
257 * @param[in,out] M The maximum order of the coefficients.
258 * @param[out] C The vector of cosine coefficients.
259 * @param[out] S The vector of sine coefficients.
260 * @param[in] truncate if false (the default) then \e N and \e M are
261 * determined by the values in the binary stream; otherwise, the input
262 * values of \e N and \e M are used to truncate the coefficients read
263 * from the stream at the given degree and order.
264 * @exception GeographicErr if \e N and \e M do not satisfy \e N &ge;
265 * \e M &ge; &minus;1.
266 * @exception GeographicErr if there's an error reading the data.
267 * @exception std::bad_alloc if the memory for \e C or \e S can't be
268 * allocated.
269 *
270 * \e N and \e M are read as 4-byte ints. \e C and \e S are resized to
271 * accommodate all the coefficients (with the \e m = 0 coefficients for
272 * \e S excluded) and the data for these coefficients read as 8-byte
273 * doubles. The coefficients are stored in column major order. The
274 * bytes in the stream should use little-endian ordering. IEEE floating
275 * point is assumed for the coefficients.
276 **********************************************************************/
277 static void readcoeffs(std::istream& stream, int& N, int& M,
278 std::vector<real>& C, std::vector<real>& S,
279 bool truncate = false);
280 };
281
282 /**
283 * Evaluate a spherical harmonic sum and its gradient.
284 *
285 * @tparam gradp should the gradient be calculated.
286 * @tparam norm the normalization for the associated Legendre polynomials.
287 * @tparam L the number of terms in the coefficients.
288 * @param[in] c an array of coeff objects.
289 * @param[in] f array of coefficient multipliers. f[0] should be 1.
290 * @param[in] x the \e x component of the cartesian position.
291 * @param[in] y the \e y component of the cartesian position.
292 * @param[in] z the \e z component of the cartesian position.
293 * @param[in] a the normalizing radius.
294 * @param[out] gradx the \e x component of the gradient.
295 * @param[out] grady the \e y component of the gradient.
296 * @param[out] gradz the \e z component of the gradient.
297 * @result the spherical harmonic sum.
298 *
299 * See the SphericalHarmonic class for the definition of the sum. The
300 * coefficients used by this function are, for example, c[0].Cv + f[1] *
301 * c[1].Cv + ... + f[L&minus;1] * c[L&minus;1].Cv. (Note that f[0] is \e
302 * not used.) The upper limits on the sum are determined by c[0].nmx() and
303 * c[0].mmx(); these limits apply to \e all the components of the
304 * coefficients. The parameters \e gradp, \e norm, and \e L are template
305 * parameters, to allow more optimization to be done at compile time.
306 *
307 * Clenshaw summation is used which permits the evaluation of the sum
308 * without the need to allocate temporary arrays. Thus this function never
309 * throws an exception.
310 **********************************************************************/
311 template<bool gradp, normalization norm, int L>
312 static Math::real Value(const coeff c[], const real f[],
313 real x, real y, real z, real a,
314 real& gradx, real& grady, real& gradz);
315
316 /**
317 * Create a CircularEngine object
318 *
319 * @tparam gradp should the gradient be calculated.
320 * @tparam norm the normalization for the associated Legendre polynomials.
321 * @tparam L the number of terms in the coefficients.
322 * @param[in] c an array of coeff objects.
323 * @param[in] f array of coefficient multipliers. f[0] should be 1.
324 * @param[in] p the radius of the circle = sqrt(<i>x</i><sup>2</sup> +
325 * <i>y</i><sup>2</sup>).
326 * @param[in] z the height of the circle.
327 * @param[in] a the normalizing radius.
328 * @exception std::bad_alloc if the memory for the CircularEngine can't be
329 * allocated.
330 * @result the CircularEngine object.
331 *
332 * If you need to evaluate the spherical harmonic sum for several points
333 * with constant \e f, \e p = sqrt(<i>x</i><sup>2</sup> +
334 * <i>y</i><sup>2</sup>), \e z, and \e a, it is more efficient to construct
335 * call SphericalEngine::Circle to give a CircularEngine object and then
336 * call CircularEngine::operator()() with arguments <i>x</i>/\e p and
337 * <i>y</i>/\e p.
338 **********************************************************************/
339 template<bool gradp, normalization norm, int L>
340 static CircularEngine Circle(const coeff c[], const real f[],
341 real p, real z, real a);
342 /**
343 * Check that the static table of square roots is big enough and enlarge it
344 * if necessary.
345 *
346 * @param[in] N the maximum degree to be used in SphericalEngine.
347 * @exception std::bad_alloc if the memory for the square root table can't
348 * be allocated.
349 *
350 * Typically, there's no need for an end-user to call this routine, because
351 * the constructors for SphericalEngine::coeff do so. However, since this
352 * updates a static table, there's a possible race condition in a
353 * multi-threaded environment. Because this routine does nothing if the
354 * table is already large enough, one way to avoid race conditions is to
355 * call this routine at program start up (when it's still single threaded),
356 * supplying the largest degree that your program will use. E.g., \code
357 GeographicLib::SphericalEngine::RootTable(2190);
358 \endcode
359 * suffices to accommodate extant magnetic and gravity models.
360 **********************************************************************/
361 static void RootTable(int N);
362
363 /**
364 * Clear the static table of square roots and release the memory. Call
365 * this only when you are sure you no longer will be using SphericalEngine.
366 * Your program will crash if you call SphericalEngine after calling this
367 * routine.
368 *
369 * \warning It's safest not to call this routine at all. (The space used
370 * by the table is modest.)
371 **********************************************************************/
372 static void ClearRootTable() {
373 std::vector<real> temp(0);
374 sqrttable().swap(temp);
375 }
376 };
377
378} // namespace GeographicLib
379
380#if defined(_MSC_VER)
381# pragma warning (pop)
382#endif
383
384#endif // GEOGRAPHICLIB_SPHERICALENGINE_HPP
Constants.hpp
Header for GeographicLib::Constants class.
GEOGRAPHICLIB_EXPORT
#define GEOGRAPHICLIB_EXPORT
Definition Constants.hpp:59
real
GeographicLib::Math::real real
Definition Geod3Solve.cpp:25
GeographicLib::CircularEngine
Spherical harmonic sums for a circle.
Definition CircularEngine.hpp:52
GeographicLib::GeographicErr
Exception handling for GeographicLib.
Definition Constants.hpp:344
GeographicLib::Math::real
double real
Definition Math.hpp:115
GeographicLib::SphericalEngine::coeff::coeff
coeff(const std::vector< real > &C, const std::vector< real > &S, int N)
Definition SphericalEngine.hpp:154
GeographicLib::SphericalEngine::coeff::coeff
coeff(const std::vector< real > &C, const std::vector< real > &S, int N, int nmx, int mmx)
Definition SphericalEngine.hpp:124
GeographicLib::SphericalEngine::coeff::N
int N() const
Definition SphericalEngine.hpp:173
GeographicLib::SphericalEngine::coeff::Sv
Math::real Sv(int k) const
Definition SphericalEngine.hpp:204
GeographicLib::SphericalEngine::coeff::Sv
Math::real Sv(int k, int n, int m, real f) const
Definition SphericalEngine.hpp:227
GeographicLib::SphericalEngine::coeff::Csize
static int Csize(int N, int M)
Definition SphericalEngine.hpp:238
GeographicLib::SphericalEngine::coeff::Ssize
static int Ssize(int N, int M)
Definition SphericalEngine.hpp:249
GeographicLib::SphericalEngine::coeff::coeff
coeff()
Definition SphericalEngine.hpp:108
GeographicLib::SphericalEngine::coeff::Cv
Math::real Cv(int k, int n, int m, real f) const
Definition SphericalEngine.hpp:215
GeographicLib::SphericalEngine::coeff::index
int index(int n, int m) const
Definition SphericalEngine.hpp:189
GeographicLib::SphericalEngine::coeff::nmx
int nmx() const
Definition SphericalEngine.hpp:177
GeographicLib::SphericalEngine::coeff::mmx
int mmx() const
Definition SphericalEngine.hpp:181
GeographicLib::SphericalEngine::coeff::Cv
Math::real Cv(int k) const
Definition SphericalEngine.hpp:197
GeographicLib::SphericalEngine::CircularEngine
friend class CircularEngine
Definition SphericalEngine.hpp:44
GeographicLib::SphericalEngine::normalization
normalization
Definition SphericalEngine.hpp:70
GeographicLib::SphericalEngine::SCHMIDT
@ SCHMIDT
Definition SphericalEngine.hpp:84
GeographicLib::SphericalEngine::FULL
@ FULL
Definition SphericalEngine.hpp:77
GeographicLib::SphericalEngine::RootTable
static void RootTable(int N)
Definition SphericalEngine.cpp:373
GeographicLib::SphericalEngine::ClearRootTable
static void ClearRootTable()
Definition SphericalEngine.hpp:372
GeographicLib
Namespace for GeographicLib.
Definition Accumulator.cpp:12