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// Write the coefficient files needed for approximating the normal gravity
// field with a GravityModel. WARNING: this creates files, wgs84.egm.cof and
// grs80.egm.cof, in the current directory.
#include <cmath>
#include <fstream>
#include <iostream>
#include <GeographicLib/NormalGravity.hpp>
#include <GeographicLib/Utility.hpp>
using namespace std;
using namespace GeographicLib;
int main() {
try {
Utility::set_digits();
const char* filenames[] = {"wgs84.egm.cof", "grs80.egm.cof"};
const char* ids[] = {"WGS1984A", "GRS1980A"};
for (int grs80 = 0; grs80 < 2; ++grs80) {
ofstream file(filenames[grs80], ios::binary);
Utility::writearray<char, char, false>(file, ids[grs80], 8);
const int N = 20, M = 0,
cnum = (M + 1) * (2 * N - M + 2) / 2; // cnum = N + 1
vector<int> num(2);
num[0] = N; num[1] = M;
Utility::writearray<int, int, false>(file, num);
vector<Math::real> c(cnum, 0);
const NormalGravity& earth(grs80 ? NormalGravity::GRS80() :
NormalGravity::WGS84());
for (int n = 2; n <= N; n += 2)
c[n] = - earth.DynamicalFormFactor(n) / sqrt(Math::real(2*n + 1));
Utility::writearray<double, Math::real, false>(file, c);
num[0] = num[1] = -1;
Utility::writearray<int, int, false>(file, num);
}
}
catch (const exception& e) {
cerr << "Caught exception: " << e.what() << "\n";
return 1;
}
catch (...) {
cerr << "Caught unknown exception\n";
return 1;
}
return 0;
}
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