VIGNOLA, Giacomo da
(b. 1507, Vignola, Bologna, d. 1573, Roma)

Perspective diagram

Biblioteca, Bologna

This illustration is from Vignola's treatise Le Due Regole della Prospettiva Practica. It shows how the observer's viewpoint is critical for understanding why an object (in this case an octagon) is depicted as it is within the artist's illusion.