MissionPlanner.Grid.PointInPolygon C# (CSharp) Method

        static bool PointInPolygon(utmpos p, List<utmpos> poly)
        {
            utmpos p1, p2;
            bool inside = false;

            if (poly.Count < 3)
            {
                return inside;
            }
            utmpos oldPoint = new utmpos(poly[poly.Count - 1]);

            for (int i = 0; i < poly.Count; i++)
            {

                utmpos newPoint = new utmpos(poly[i]);

                if (newPoint.y > oldPoint.y)
                {
                    p1 = oldPoint;
                    p2 = newPoint;
                }
                else
                {
                    p1 = newPoint;
                    p2 = oldPoint;
                }

                if ((newPoint.y < p.y) == (p.y <= oldPoint.y)
                    && ((double)p.x - (double)p1.x) * (double)(p2.y - p1.y)
                    < ((double)p2.x - (double)p1.x) * (double)(p.y - p1.y))
                {
                    inside = !inside;
                }
                oldPoint = newPoint;
            }
            return inside;
        }