The three basic camera properties are its position, the direction in which it is pointing, and its orientation. The keywords for specifying these values are described below. The default values are designed to provide a reasonable view of a sphere of radius 2 located at origin. If these default values are used, the origin is projected onto the center of the image plane, with the world x axis running left-to-right, the z axis bottom-to-top, and the y axis going ``into'' the screen.
Another popular standard viewing geometry, with the x axis running left-to-right, the y axis bottom-to-top, and the z axis pointing out of the screen, may be obtained by setting the up vector to (0, 1, 0) and by placing the camera on the positive z axis.