ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-Geoid.cpp

@@ -0,0 +1,27 @@
+// Example of using the GeographicLib::Geoid class
+// This requires that the egm96-5 geoid model be installed; see
+// https://geographiclib.sourceforge.io/C++/doc/geoid.html#geoidinst
+
+#include <iostream>
+#include <exception>
+#include <GeographicLib/Geoid.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  try {
+    Geoid egm96("egm96-5");
+    // Convert height above egm96 to height above the ellipsoid
+    double lat = 42, lon = -75, height_above_geoid = 20;
+    double
+      geoid_height = egm96(lat, lon),
+      height_above_ellipsoid = (height_above_geoid +
+                                Geoid::GEOIDTOELLIPSOID * geoid_height);
+    cout << height_above_ellipsoid << "\n";
+  }
+  catch (const exception& e) {
+    cerr << "Caught exception: " << e.what() << "\n";
+    return 1;
+  }
+}