3D-picking

Picking is the process of finding objects in your scene based on user input. Most commonly, you want to determine what object a user has clicked with his mouse. The 2D mouse coordinates serve as a reference on the view port to identify the projected objected that has been clicked. A similar scenario is a first person shooter, where the gun is basically the picking pointer. If you shoot the gun, the trajectory of the bullet is traced through the scene and collisions are detected, similar to a laser pointer shooting a ray through a scene until it hits an object and marks it with a small red dot.