There are various methods for judging the angles of vanishing lines. The one that works best for me is to visualize it as the hour hand on a clock.
I do it like this: The minute hand serves as either the horizon line (the position it's at 9 or 3 o'clock) or a vertical (12 o'clock). Then I look at the vanishing line, and think of it as being the hour hand on a clock. I then read "the time", and remember this as I mark it on my painting.
Thus, in the photo, the vanishing line at foot level is coming up at about eight o'clock. And the vanishing line above the figure's head is coming in at about ten o'clock. (The photo is of The Art Bin.)