ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-AlbersEqualArea.cpp

@@ -0,0 +1,39 @@
+// Example of using the GeographicLib::AlbersEqualArea class
+
+#include <iostream>
+#include <exception>
+#include <GeographicLib/AlbersEqualArea.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  try {
+   const double
+     a = Constants::WGS84_a(),
+     f = Constants::WGS84_f(),
+     lat1 = 40 + 58/60.0, lat2 = 39 + 56/60.0, // standard parallels
+     k1 = 1,                                   // scale
+     lon0 = -77 - 45/60.0;                     // Central meridian
+   // Set up basic projection
+   const AlbersEqualArea albers(a, f, lat1, lat2, k1);
+   {
+     // Sample conversion from geodetic to Albers Equal Area
+     double lat = 39.95, lon = -75.17;    // Philadelphia
+     double x, y;
+     albers.Forward(lon0, lat, lon, x, y);
+     cout << x << " " << y << "\n";
+   }
+   {
+     // Sample conversion from Albers Equal Area grid to geodetic
+     double x = 220e3, y = -53e3;
+     double lat, lon;
+     albers.Reverse(lon0, x, y, lat, lon);
+     cout << lat << " " << lon << "\n";
+   }
+  }
+  catch (const exception& e) {
+    cerr << "Caught exception: " << e.what() << "\n";
+    return 1;
+  }
+}