Solid Geometry is a 2002 short TV film directed by Denis Lawson and starring his nephew Ewan McGregor and Ruth Millar.
It is based on a short story by Ian McEwan published in collection First Love, Last Rites.
He becomes obsessed with research into solid geometry contained in the diaries and is fascinated by the theory of "a plane without a surface."
He goes on to become obsessed with this transformation and the discussion in the book which links it to 'sexual intercourse positions' of which the diary claims there are only 17.
After a love-making session with his wife, he proceeds to place another of the paper lotus flowers in the center of her curled body.