All lines situated in a plane that is parallel to the picture plane diminish in proportion as they become more distant, but do not undergo any perspective deformation. This is called the front view.
Rule 5
All horizontal lines which are at right angles to the picture plane are drawn to the point of sight.
Rule 6
All horizontals which are at 45° to the picture plane are drawn to the point of distance.
Rule 7
All horizontals forming any other angles but the above are drawn to some other points on the horizontal line.
Rule 8
Lines which incline upwards have their vanishing points above the horizon, and those which incline downwards, below it. In both cases they are on the vertical which passes through the vanishing point of their ground-plan or horizontal projections.