ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-Geohash.cpp

@@ -0,0 +1,45 @@
+// Example of using the GeographicLib::Geohash class
+
+#include <iostream>
+#include <iomanip>
+#include <exception>
+#include <string>
+#include <GeographicLib/Geohash.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  try {
+    {
+      // Sample forward calculation
+      double lat = 57.64911, lon = 10.40744; // Jutland (the wikipedia example)
+      string geohash;
+      int maxlen = Geohash::GeohashLength(1.0e-5);
+      for (int len = 0; len <= maxlen; ++len) {
+        Geohash::Forward(lat, lon, len, geohash);
+        cout << len << " " << geohash << "\n";
+      }
+    }
+    {
+      // Sample reverse calculation
+      string geohash = "u4pruydqqvj";
+      double lat, lon, latres, lonres;
+      cout << fixed;
+      for (unsigned i = 0; i <= geohash.length(); ++i) {
+        int len;
+        Geohash::Reverse(geohash.substr(0, i), lat, lon, len);
+        latres = Geohash::LatitudeResolution(len);
+        lonres = Geohash::LongitudeResolution(len);
+        cout << setprecision(max(0, Geohash::DecimalPrecision(len)))
+             << len << " "
+             << lat << "+/-" << latres/2 << " "
+             << lon << "+/-" << lonres/2 << "\n";
+      }
+    }
+  }
+  catch (const exception& e) {
+    cerr << "Caught exception: " << e.what() << "\n";
+    return 1;
+  }
+}