How to set the viewing volume in OpenGL ES for an iPhone AR app?

I'd like to add an OpenGL ES view as an overlay to my camera view. From this question and its anser I came to know the two field angles of the iPhone 4 rear camera.

How can I properly set the volume view and its perspective in the OpenGL ES view? Shall I use glFrustum or glOrthof?

(I've seen that gluPerspective takes jus开发者_如何学Pythont one angle as parameter, is it supposing to have a square frustum instead of a rectangular one?)

It seems that this can be accomplished by using simple trigonometry functions ^^. Just have a look at what a frustrum is, and which values are needed by glFrustum (have a look at this page). This stated, I do not believe that the values reported on the linked answer are the correct ones since they apply a distortion (kind of scaling along an axis) to the rendered images.