BEPUphysics.CollisionShapes.TerrainShape.GetNormal C# (CSharp) Method

        public void GetNormal(int i, int j, ref AffineTransform transform, out Vector3 normal)
        {
            Vector3 top;
            Vector3 bottom;
            Vector3 right;
            Vector3 left;

            if (i <= 0)
                i = 0;
            else if (i >= heights.GetLength(0))
                i = heights.GetLength(0) - 1;
            if (j <= 0)
                j = 0;
            else if (j >= heights.GetLength(1))
                j = heights.GetLength(1) - 1;

            GetPosition(i, Math.Min(j + 1, heights.GetLength(1) - 1), ref transform, out top);
            GetPosition(i, Math.Max(j - 1, 0), ref transform, out bottom);
            GetPosition(Math.Min(i + 1, heights.GetLength(0) - 1), j, ref transform, out right);
            GetPosition(Math.Max(i - 1, 0), j, ref transform, out left);

            Vector3 temp;
            Vector3.Subtract(ref top, ref bottom, out temp);
            Vector3.Subtract(ref right, ref left, out normal);
            Vector3.Cross(ref temp, ref normal, out normal);

            normal.Normalize();
        }