[tobr]

Surely this introduces some curvature to the diagonals? I can't see how the perpendicular lines can be in correct perspective with the diagonals being parallel unless something is curving. I guess because it's preserving the perpendicular lines and the curvature is subtle, it's not very noticeable in typical architectural pictures.

[JKCalhoun]

Curvature maybe — "skew" seems more likely.

[account42]

It's not a real projection as in a panosphere -> rectangle mapping but rather a local transformation of specific objects.