In his letter in the March 1995 issue of the Gazette (79, p. 123), John Sharp points out that the correct viewing position for a picture is with the eye opposite the central vanishing point, that is, on the normal to the picture plane at the point of meeting of all lines in the scene represented that are perpendicular to the picture plane. In order to obtain a true view of the scene depicted, it is also necessary that the eye be placed at the correct distance from the picture.