Perceptual Constancies- Shape Constancy

This is when we perceive a certain shape to be different at certain angles.

 Like when we look at a plate- we know it is a circle, but when we observe it at a certain angle it looks like a half-moon.

Another example is when we look at a door. Unopened, it is a rectangle. But as it opens more and more, it gets thinner and thinner.