I just want to let people interested in automatically computing viewpoints in a game (e.g. replay cameras in driving games, or cinematic cameras) that there is a new open-source C++ library for that, called Smart Viewpoint Computation Lib, and available at https://bitbucket.org/rranon/smart-viewpoint-computation-lib
SmartViewpointComputationLib is a C++ library to compute the best viewpoint in a 3D scene that satisfies a set of visual properties, such as size, visibility or angle of selected objects in the scene. For example, suppose you have a building floor scene like this one:
Other kinds of properties include the orientation of objects with respect to the viewpoint (i.e., camera angle in photography terms), framing an object in specific parts of the screen, and relative position on screen of two objects (e.g., one at the left of the other). In other words, you can find viewpoints like you would compose a picture, leaving to the library the task of positioning and aiming the camera.
The library does not make any assumption on the scene and objects, and only require access to the scene objects' meshes and world transformations. It can return a result within a time of your choice (e.g., a few tens of milliseconds). More time will generally increase the quality of results, especially in large and complex scenes.
The library comes with bindings for the Ogre open-source rendering engine. Connecting it to other rendering engines, however, requires to modify just one header file (which for Ogre consists of 500 lines of code).
If you are interested, give it a look!