When can the Camera see Me?

I'm looking for a quick and easy way to tell if a vector or invisible model is within the camera viewpoint. That way I can start an action only when it is not visible from the camera view.

Can this be done without having to compare the model's and camera's x/y coordinates and thier distance to each other, and then comparing that with the camera's angle and taking into account the camera's arc? That just seems overly complicated. Or maybe there's a good algorithm that takes all this into account in just a few lines. Any ideas?

Quote:

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entity.clipped

Tells wether an entity is was clipped away by the culling process during the last frame. Can be evaluated for running entity functions - for instance, particles - depending on whether the entiy is potentially visible or not.

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