ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-CircularEngine.cpp

@@ -0,0 +1,35 @@
+// Example of using the GeographicLib::CircularEngine class
+
+#include <iostream>
+#include <exception>
+#include <vector>
+#include <GeographicLib/CircularEngine.hpp>
+#include <GeographicLib/SphericalHarmonic.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  // This computes the same value as example-SphericalHarmonic.cpp using a
+  // CircularEngine (which will be faster if many values on a circle of
+  // latitude are to be found).
+  try {
+    using std::hypot;
+    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);
+    double a = 1;
+    SphericalHarmonic h(C, S, N, a);
+    double x = 2, y = 3, z = 1, p = hypot(x, y);
+    CircularEngine circ = h.Circle(p, z, true);
+    double v, vx, vy, vz;
+    v = circ(x/p, y/p, vx, vy, vz);
+    cout << v << " " << vx << " " << vy << " " << vz << "\n";
+  }
+  catch (const exception& e) {
+    cerr << "Caught exception: " << e.what() << "\n";
+    return 1;
+  }
+}