ADD: new track message, Entity class and Position class

libs/geographiclib/examples/example-PolygonArea.cpp

@@ -0,0 +1,40 @@
+// Example of using the GeographicLib::PolygonArea class
+
+#include <iostream>
+#include <exception>
+#include <GeographicLib/PolygonArea.hpp>
+#include <GeographicLib/Geodesic.hpp>
+#include <GeographicLib/Constants.hpp>
+
+using namespace std;
+using namespace GeographicLib;
+
+int main() {
+  try {
+    Geodesic geod(Constants::WGS84_a(), Constants::WGS84_f());
+    // Alternatively: const Geodesic& geod = Geodesic::WGS84();
+    PolygonArea poly(geod);
+    poly.AddPoint( 52,  0);     // London
+    poly.AddPoint( 41,-74);     // New York
+    poly.AddPoint(-23,-43);     // Rio de Janeiro
+    poly.AddPoint(-26, 28);     // Johannesburg
+    double perimeter, area;
+    unsigned n = poly.Compute(false, true, perimeter, area);
+    cout << n << " " << perimeter << " " << area << "\n";
+    // This adds a test for a bug fix for AddEdge.  (Implements the
+    // Planimeter29 test in geodtest.c.)
+    PolygonArea poly1(geod);
+    poly1.AddPoint(0,0);
+    poly1.AddEdge(90,1000);
+    poly1.AddEdge(0,1000);
+    poly1.AddEdge(-90,1000);
+    n = poly1.Compute(false, true, perimeter, area);
+    // The area should be 1e6.  Prior to the fix it was 1e6 - A/2, where
+    // A = ellipsoid area.
+    cout << n << " " << perimeter << " " << area << "\n";
+  }
+  catch (const exception& e) {
+    cerr << "Caught exception: " << e.what() << "\n";
+    return 1;
+  }
+}