ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-Geocentric.cpp

@@ -0,0 +1,36 @@
+// Example of using the GeographicLib::Geocentric class
+
+#include <iostream>
+#include <exception>
+#include <cmath>
+#include <GeographicLib/Geocentric.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  try {
+    Geocentric earth(Constants::WGS84_a(), Constants::WGS84_f());
+    // Alternatively: const Geocentric& earth = Geocentric::WGS84();
+    {
+      // Sample forward calculation
+      double lat = 27.99, lon = 86.93, h = 8820; // Mt Everest
+      double X, Y, Z;
+      earth.Forward(lat, lon, h, X, Y, Z);
+      cout << floor(X / 1000 + 0.5) << " "
+           << floor(Y / 1000 + 0.5) << " "
+           << floor(Z / 1000 + 0.5) << "\n";
+    }
+    {
+      // Sample reverse calculation
+      double X = 302e3, Y = 5636e3, Z = 2980e3;
+      double lat, lon, h;
+      earth.Reverse(X, Y, Z, lat, lon, h);
+      cout << lat << " " << lon << " " << h << "\n";
+    }
+  }
+  catch (const exception& e) {
+    cerr << "Caught exception: " << e.what() << "\n";
+    return 1;
+  }
+}