(Information from the YouTube entry which follows)
As Mr Longo is still around, still working, I shall resist posting his natal chart, but for anyone interested there's a 12 noon version of it at Astrotheme here. Key placements for me, relevant to his art style, are Capricorn Sun opposite Uranus in Cancer with two loose squares to a conjunction of Neptune and Saturn in Libra the sign ruled by Venus, planet of the arts, forming a T-square. This indicates tension between tradition and modernity, fact and imagination. Though Mr Longo's style is modern in concept, he relies strongly on chiaroscuro (light-dark), an oil painting technique, developed during the Renaissance, using strong tonal contrasts between light and dark to model three-dimensional forms. Also, his natal Sun trines Jupiter in Taurus (the other sign ruled by Venus), Jupiter representing exaggeration and excess is reflected in the huge size of much of his artwork.
Just a sidelight: facially Mr Longo is what I think of as typically Capricorn-looking.
Robert Longo's charcoal drawings can easily be mistaken for photographs, especially when viewed online. He does use photographs as guides when creating his artwork, but his drawings are all by freehand - no computer acrobatics involved.
A handful of examples of Robert Longo's artwork - many more at Google Image here. There are also several more YouTube presentations and interviews relating to Mr Longo and his artworks.