example-PolygonArea.cpp

// 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;
  }
}