This is where it gets a tad tricky. To finish off the cubes, we have to draw the third side on all necessary cubes. For any cube floating above the horizon line, we will draw the bottom side of the cube by drawing a lines from the bottom tips of the side edges of the cube leading to the opposite vanishing point. Similarly, for any cube floating beneath the horizon line, we will draw the top side of the cube by drawing a lines from the top tips of the side edges of the cube leading to the opposite vanishing point. Note that any cube who's front edge runs through the horizon line will not require a third edge, as it is hidden from our perspective.