The maximal orthogonal convex hull is what is left of the plane when you take away all set-free quadrants, that is basically the intersection of the sets 1,2,3 below plus cutting off the rest outside the rectangle (I have shown only three the most important quadrants on the pictures as the others cannot penetrate in the rectangle, so they make the obvious cut - the same as half-planes). The intersection then is precisely the set drawn on the figure 3 above. In your answer it looks like you are taking away half-planes (less freedom) instead of the quadrants, that's why you get it different. By the way, the inside part of your rectangle seems to be empty. If so, how did you cut it off?![Set 1](
![Set 2](
![Set 3](