In two-point perspective the vertical edges stay vertical. That is true when you look straight ahead. But tip your head back to look at the top of a skyscraper, and the sides of the building seem to lean in toward each other high above you. Now even the vertical edges meet, at a third vanishing point.
Key idea
Three-point perspective adds a third vanishing point for the vertical edges: above the object when you look far up (a worm's-eye view), below it when you look far down (a bird's-eye view).
Why it works
Vertical edges stay vertical only while they are flat to you, which happens when you look straight ahead. Tilt your view up or down and those edges now go away from you too. Any set of parallel edges that goes away from you meets at its own vanishing point.
Worked example: Which kind?
You draw a tall tower from its base, looking almost straight up. How many vanishing points?
- The two sides of the tower go back left and right: two points on the horizon.
- You look far up, so the vertical edges also go away from you.
- They meet at a third point high above.
Answer: Three.
Common mistake
Some people add a third vanishing point to every drawing to make it look advanced. For an ordinary eye-level view of a house or a box, the vertical edges should stay vertical. Save three-point for views that look far up or far down.
Photographs of tall buildings taken from the street often show the sides leaning inward, like the Chrysler Building seen from below.