This illustration is made to be observed the eye 150 cm away from the paper for geometrical reasons, the spherical correction has been made with the computer.

The pattern is made of boxes with different densities

The construction is rigorous (middle scheme) : the horizon line is the top border ot he paper. The perspective point is in the right hand corner. The diagonales divide the composition in 2 equal parts (lower scheme).

The shadow of the box appears darker than the dark side of the box. The border of the shadow is darker than the body of the shadow as we can oberve in reality (top scheme).