Question: In The Vitruvian Man, on whose work was Leonardo's notes based upon?
About the article "Vitruvian Man", section "Abstract".

Candidate passages:
Leonardo's robot or Leonardo's mechanical knight refers to a humanoid automaton designed by Leonardo da Vinci around the year 1495.
The design notes for the robot appear in sketchbooks that were rediscovered in the 1950s.
Leonardo displayed his "robot" at a celebration hosted by Ludovico Sforza at the court of Milan in 1495.
The robot knight could stand, sit, raise its visor and independently maneuver its arms.
The entire robotic system was operated by a series of pulleys and cables.
Since the discovery of the sketchbook, the robot has been built faithfully based on Leonardo's design; this proved it was fully functional, as Leonardo had planned.
The robot is clad in German-Italian medieval armour, that is able to make several human-like motions.
These motions included sitting up, moving its arms, neck, and an anatomically correct jaw.
Also it was most likely planned to be made with fluidity in combat.
It is partially the fruit of Leonardo's anatomical research in the Canon of Proportions as described in the "Vitruvian Man". 
The Vitruvian Man, , is a drawing created by Leonardo da Vinci circa 1490.
It is accompanied by notes based on the work of the architect Vitruvius.
The drawing, which is in pen and ink on paper, depicts a male figure in two superimposed positions with his arms and legs apart and simultaneously inscribed in a circle and square.
The drawing and text are sometimes called the "Canon of Proportions" or, less often, "Proportions of Man".
It is kept in the Gabinetto dei disegni e stampe of the Gallerie dell'Accademia, in Venice, Italy, under reference 228.
Like most works on paper, it is displayed to the public only occasionally.
The drawing is based on the correlations of ideal human proportions with geometry described by the ancient Roman architect Vitruvius in Book III of his treatise "De Architectura".
Vitruvius described the human figure as being the principal source of proportion among the Classical orders of architecture.
Vitruvius determined that the ideal body should be eight heads high.
Leonardo's drawing is traditionally named in honor of the architect.
In 1502 Leonardo da Vinci produced a drawing of a single-span bridge over the Golden Horn as part of a civil engineering project for Sultan Bayezid II.
Leonardo's drawings and notes regarding this bridge are currently displayed at the Museo della Scienza e della Tecnologia in Milan, Italy.
The vision of Leonardo's Golden Horn Bridge was resurrected in 2001, when a small footbridge based on Leonardo's design was constructed near Ås in Norway. 
Leonardo's face is best known from a drawing in red chalk that appears to be a self-portrait.
However, there is some controversy over the identity of the subject, because the man represented appears to be of a greater age than the 67 years lived by Leonardo.
A solution which has been put forward is that Leonardo deliberately aged himself in the drawing, as a modern forensic artist might do, in order to provide a model for Raphael's painting of him as Plato in "The School of Athens".
A profile portrait in the Ambrosiana Gallery in Milan is generally accepted to be a portrait of Leonardo, and also depicts him with flowing beard and long hair.
This image was repeated in the woodcut designed for the first edition of Vasari's "Lives".
In a 2008 TED talk, artist Siegfried Woldhek, based on Leonardo's features in Andrea del Verrocchio's bronze statue of "David", proposed that Leonardo may have done three self-portraits: "Portrait of a Musician", the "Vitruvian Man" and the aforementioned "Portrait of a man in red chalk". 
Evidence has been found that Leonardo might have been influenced by the work of Giacomo Andrea de Ferrara, a Renaissance architect, expert on Vitruvius, and close friend of his.
Giacomo Andrea's original drawing has only one set of arms and legs while Leonardo's has the position of his man's arms and legs change.
Another possible influence for Leonardo's depiction could have been the codex depictions of human proportions in architecture by Francesco di Giorgio, a Sienese architect who compiled an unpublished "Trattato di Architettura Civile e Militare" in 1470.