Projective differential geometry

Projective differential geometry is a way of studying shapes and angles in geometry. It looks at how angles and lines change when viewed from different distances or when projected onto another surface. For example, if you take a square and draw a line from one corner to another, it looks like a straight line. But when you draw it from a different distance, it looks curved. Projective differential geometry looks at the different ways shapes and angles can change or look different depending on how they are viewed.