Look-at positioning
Find the viewing transform given the eye (camera) position, point to look at, and the up vector
- Need to specify two transforms: rotation and translation.
- translation is easy
- natural rotation: define implicitly using a point at which we want to look and a vector indicating the vertical in the image (up vector)
can easily convert the eye point to the direction vector of the camera axis; can assume up vector perpendicular to view vector