GeographicLib  1.30
GeographicLib::SphericalEngine Class Reference

The evaluation engine for SphericalHarmonic. More...

#include <GeographicLib/SphericalEngine.hpp>

## Classes

class  coeff
Package up coefficients for SphericalEngine. More...

## Public Types

enum  normalization { FULL, SCHMIDT }

## Static Public Member Functions

template<bool gradp, normalization norm, int L>
static Math::real Value (const coeff c[], const real f[], real x, real y, real z, real a, real &gradx, real &grady, real &gradz) throw ()

template<bool gradp, normalization norm, int L>
static CircularEngine Circle (const coeff c[], const real f[], real p, real z, real a)

static void RootTable (int N)

static void ClearRootTable ()

## Friends

class CircularEngine

## Detailed Description

The evaluation engine for SphericalHarmonic.

This serves as the backend to SphericalHarmonic, SphericalHarmonic1, and SphericalHarmonic2. Typically end-users will not have to access this class directly.

Example of use:

// Example of using the GeographicLib::SphericalEngine class
#include <iostream>
#include <exception>
#include <vector>
using namespace std;
using namespace GeographicLib;
int main() {
try {
int N = 3; // The maxium degree
double ca[] = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1}; // cosine coefficients
vector<double> C(ca, ca + (N + 1) * (N + 2) / 2);
double sa[] = {6, 5, 4, 3, 2, 1}; // sine coefficients
vector<double> S(sa, sa + N * (N + 1) / 2);
c[0] = SphericalEngine::coeff(C, S, N);
double f[] = {1};
double x = 2, y = 3, z = 1, a = 1;
double v, vx, vy, vz;
v = SphericalEngine::Value<true, SphericalEngine::FULL, 1>
(c, f, x, y, z, a, vx, vy, vz);
cout << v << " " << vx << " " << vy << " " << vz << "\n";
}
catch (const exception& e) {
cerr << "Caught exception: " << e.what() << "\n";
return 1;
}
return 0;
}

Definition at line 40 of file SphericalEngine.hpp.

## Member Enumeration Documentation

Supported normalizations for associated Legendre polynomials.

Enumerator:
 FULL Fully normalized associated Legendre polynomials. See SphericalHarmonic::FULL for documentation. SCHMIDT Schmidt semi-normalized associated Legendre polynomials. See SphericalHarmonic::SCHMIDT for documentation.

Definition at line 57 of file SphericalEngine.hpp.

## Member Function Documentation

template<bool gradp, SphericalEngine::normalization norm, int L>
 Math::real GeographicLib::SphericalEngine::Value ( const coeff c[], const real f[], real x, real y, real z, real a, real & gradx, real & grady, real & gradz ) throw ()
static

Evaluate a spherical harmonic sum and its gradient.

Template Parameters
 gradp should the gradient be calculated. norm the normalization for the associated Legendre polynomials. L the number of terms in the coefficients.
Parameters
 [in] c an array of coeff objects. [in] f array of coefficient multipliers. f[0] should be 1. [in] x the x component of the cartesian position. [in] y the y component of the cartesian position. [in] z the z component of the cartesian position. [in] a the normalizing radius. [out] gradx the x component of the gradient. [out] grady the y component of the gradient. [out] gradz the z component of the gradient.
Returns
the spherical harmonic sum.

See the SphericalHarmonic class for the definition of the sum. The coefficients used by this function are, for example, c[0].Cv + f[1] * c[1].Cv + ... + f[L−1] * c[L−1].Cv. (Note that f[0] is not used.) The upper limits on the sum are determined by c[0].nmx() and c[0].mmx(); these limits apply to all the components of the coefficients. The parameters gradp, norm, and L are template parameters, to allow more optimization to be done at compile time.

Clenshaw summation is used which permits the evaluation of the sum without the need to allocate temporary arrays. Thus this function never throws an exception.

Definition at line 157 of file SphericalEngine.cpp.

References GeographicLib::Math::hypot(), GeographicLib::Math::sq(), and STATIC_ASSERT.

template<bool gradp, SphericalEngine::normalization norm, int L>
 CircularEngine GeographicLib::SphericalEngine::Circle ( const coeff c[], const real f[], real p, real z, real a )
static

Create a CircularEngine object

Template Parameters
 gradp should the gradient be calculated. norm the normalization for the associated Legendre polynomials. L the number of terms in the coefficients.
Parameters
 [in] c an array of coeff objects. [in] f array of coefficient multipliers. f[0] should be 1. [in] p the radius of the circle = sqrt(x2 + y2). [in] z the height of the circle. [in] a the normalizing radius.
Exceptions
 std::bad_alloc if the memory for the CircularEngine can't be allocated.
Returns
the CircularEngine object.

If you need to evaluate the spherical harmonic sum for several points with constant f, p = sqrt(x2 + y2), z, and a, it is more efficient to construct call SphericalEngine::Circle to give a CircularEngine object and then call CircularEngine::operator()() with arguments x/p and y/p.

Definition at line 299 of file SphericalEngine.cpp.

 void GeographicLib::SphericalEngine::RootTable ( int N )
static

Check that the static table of square roots is big enough and enlarge it if necessary.

Parameters
 [in] N the maximum degree to be used in SphericalEngine.
Exceptions
 std::bad_alloc if the memory for the square root table can't be allocated.

Typically, there's no need for an end-user to call this routine, because the constructors for SphericalEngine::coeff do so. However, since this updates a static table, there's a possible race condition in a multi-threaded environment. Because this routine does nothing if the table is already large enough, one way to avoid race conditions is to call this routine at program start up (when it's still single threaded), supplying the largest degree that your program will use. E.g.,

suffices to accommodate extant magnetic and gravity models.

Definition at line 374 of file SphericalEngine.cpp.

Referenced by GeographicLib::SphericalEngine::coeff::coeff().

 static void GeographicLib::SphericalEngine::ClearRootTable ( )
inlinestatic

Clear the static table of square roots and release the memory. Call this only when you are sure you no longer will be using SphericalEngine. Your program will crash if you call SphericalEngine after calling this routine. It's safest not to call this routine at all. (The space used by the table is modest.)

Definition at line 360 of file SphericalEngine.hpp.

## Friends And Related Function Documentation

 friend class CircularEngine
friend

Definition at line 45 of file SphericalEngine.hpp.

The documentation for this class was generated from the following files: