An aimed hole
The clappers of this door in Rome on the Aventino have a dihedral symmetry D1 and if you look inside the hole, you see that it is aimed exactly over the cupola of S. Pietro.
© matematita
The image belongs to the sections...:
* (D1) (Symmetry)
Door knockers (Anthology of images)
Door knockers (Symmetry)
Doors and windows (Anthology of images)
Viewpoint (3D geometry)
