ABSTRACT
An operation frequently used in three-dimensional (3D) graphics applications is to pick or select an object from the screen. Another is to rotate an object, for example, by sliding a finger on a touch screen. Such object picking and rotating algorithms are seemingly complicated but are implemented by combining the transforms we have learned so far. On a touch screen, an object can be picked by tapping it with a finger. An object in a touch screen can spin by placing a finger on the screen and sliding it. The object will be rotated and then displayed on the screen. For this, the rotation axis should be redefined in the object space so that the rotation is made sprior to the original world transform. The camera-space axis will be transformed back to the world space and then to the object space using the inverses of the view and world transforms.
