How can I compare the location of a quad with the location of the view frustum?


When a player moves inside a level (indoor), when he is in a room, he may see another room visible from a portal and I need to know where the portal is located compared with the view frustum in order to create another frustum that contains only what is visible from this portal. Could the method getScreenCoordinates(Vector3f worldPosition) of the class Camera be useful in my case? I would like to project this portal onto the near plane of the view frustum.