This is a bit of a newbie question, but if for example, I want to extend the scene manager, and add a function; do I extend my class (inherit) from CSceneManager or ISceneManager?

Because I'm trying this in MySceneManager.h: #include <CSceneManager.h>

class RTSSceneManager : public CSceneManager
{
    virtual ICameraSceneNode* addCameraSceneNodeRTS(ISceneNode* parent = 0,
            const core::vector3df& position = core::vector3df(0,0,0),
            const core::vector3df& lookat = core::vector3df(0,0,100),
            s32 id=-1, bool makeActive=true) = 0;
};

But it's giving me this error:

fatal error C1083: Cannot open include file: 'CSceneManager.h': No such file or directory

It works if I use ISceneManager instead of CSceneManager, but then won't I have to re implement CSceneManager over again?