Bear in mind this wasn't drawn from life. Here's the difference between the view when I walk along looking straight ahead, and the view when I stoop and stare at the pavement some way ahead of me, say 8 feet ahead.
The yellow grid was to give me a reference of true vertical and horizontals on the picture plane. Then I plotted in the vanishing point. On the left is the classic vanishing point on the horizon. On the right the vanishing point drops with respect to the position of the pavement and imagined buildings either side.