Wouldn’t it be cool to have goggles that showed you exactly how far away from you a bird or a plane or a planet is? Here’s a first step at understanding the math behind a project like that, basically, understanding parallax. What else would you have to know? Would you have to know the size of the object first?
An article: https://www.khanacademy.org/science/in-in-class11th-physics/in-in-11th-physics-units-and-measurement/in-in-11th-physics-physical-quantities-and-their-measurement/a/parallax-distance