Refactor

algorithms/geometry/geometry_functions.cpp

+/**
+ * Geometry functions
+ */
+
+struct Vector {
+  double x, y; 
+
+  Vector(double x, double y) : x(x), y(y) {}
+
+  double dot_product(Vector v) { return x * v.x + y * v.y; }
+  double cross_product(Vector v) { return x * v.y - v.x * y; }
+
+  /**
+   * Returns angle between this and v.
+   */
+  double angle(Vector v) {
+
+    // atan2(y, x) is in the range [-180,180]. To get [0, 360], 
+    // atan2(-y, -x) + 180 is used
+    return ((atan2(-cross_product(v), -dot_product(v)) * 180.0) / M_PI) + 180.0;
+  }
+};