Transliterated from java found here:

class ConvexHull
{
public static double cross(Point O, Point A, Point B)
{
return (A.X - O.X) * (B.Y - O.Y) - (A.Y - O.Y) * (B.X - O.X);
}
public static List<Point> GetConvexHull(List<Point> points)
{
if (points == null)
return null;
if (points.Count() <= 1)
return points;
int n = points.Count(), k = 0;
List<Point> H = new List<Point>(new Point[2 * n]);
points.Sort((a, b) =>
a.X == b.X ? a.Y.CompareTo(b.Y) : a.X.CompareTo(b.X));
// Build lower hull
for (int i = 0; i < n; ++i)
{
while (k >= 2 && cross(H[k - 2], H[k - 1], points[i]) <= 0)
k--;
H[k++] = points[i];
}
// Build upper hull
for (int i = n - 2, t = k + 1; i >= 0; i--)
{
while (k >= t && cross(H[k - 2], H[k - 1], points[i]) <= 0)
k--;
H[k++] = points[i];
}
return H.Take(k - 1).ToList();
}
}

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