The Last Supper - Vanishing Points The vanishing point seems to be at the center of the frame, where the parallel lines seem to meet.
I am wondering why the parallel lines of the semi arch are pointing down.
Any pointer would be helpful.
Please excuse my ignorance. Thank you!
The arch is not a painted part of the painting, but a physical part of the room in the Santa Maria delle Grazie above which the mural can be found:

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