Ossim Planet Primer
The camera, or eye, is a point above the planet surface that has a degree of vertical tilt.
Line of Sight
The position on the surface directly under the center of the screen. If the center of the screen does not cross the surface, this value is infinite, with lat/long of zero.
The point on the surface of the planet that is between the camera and the planet center.
The Eye Point is a point provided by a NodeVisitor. This point is the position of the eye, relative to the node. This allows you to get the distance between the two by calling eyePoint.length().