In his sketch (fig. 2) for the composition (fig. 3), Vittore Carpaccio
(1450–1526) consistently used constructive linear frontal perspective.
However, in the painting itself, in some architectural elements (such
as balconies with brackets, the porch with columns, eaves on the side)
he used parallel bearing not converging towards the vanishing point.
Had it not been represented as a rhomboid, the balcony would appear
small, malformed, insufficiently clear. Also, the line that links the
columns with the terrain, which does not lead to the vanishing point
but is almost parallel to the horizon, stabilizes the composition and,
simultaneously, intensifies the reality of the representation.

Can anyone explain ?