Object appears in camera? How can I investigate if an object appears through a camera in BGE?

Ray sensor does not suit me cause it is one line, while I am searching for the whole screen.
As far as I know the API does not provide direct access to the frustum calculation. 

You can use KX_Camera.boxInsideFrustum, KX_Camera.sphereInsideFrustum and bge.types.KX_Camera.pointInsideFrustum to get an estimate if something is at the screen (or maybe not).