ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-MagneticModel.cpp

@@ -0,0 +1,26 @@
+// Example of using the GeographicLib::MagneticModel class
+// This requires that the wmm2010 magnetic model be installed; see
+// https://geographiclib.sourceforge.io/C++/doc/magnetic.html#magneticinst
+
+#include <iostream>
+#include <exception>
+#include <GeographicLib/MagneticModel.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  try {
+    MagneticModel mag("wmm2010");
+    double lat = 27.99, lon = 86.93, h = 8820, t = 2012; // Mt Everest
+    double Bx, By, Bz;
+    mag(t, lat,lon, h, Bx, By, Bz);
+    double H, F, D, I;
+    MagneticModel::FieldComponents(Bx, By, Bz, H, F, D, I);
+    cout << H << " " << F << " " << D << " " << I << "\n";
+  }
+  catch (const exception& e) {
+    cerr << "Caught exception: " << e.what() << "\n";
+    return 1;
+  }
+}