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I have 4 angles, left, right, top & bottom. These angles are in degrees. They define the angle between the forward vector and the corresponding side. I am trying to use these to calculate the required values for Perseective Off Centre function found here I tried doing (near plane-far plane) * Tan(angle) But that didn't give the correct results.

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up vote 1 down vote accepted

You have to know exactly what you're looking for. I believe TOP in the referenced link here refers to what I call o in the diagram below.

enter image description here

You just need to complete this for every angle. Keep in mind the far plane is measured from eye TO the far plane, and so is the Near plane. Both near and far should always be positive because they measure a distance from the eye. So you don't do far plane - near plane and you definitely don't do near plane - far plane (that will always be a large negative value).

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That is a very similar diagram to what I had on paper :). I see what I did wrong. Don't know why I tried 'near - far'. I'll try it out and let you know if it works. Thank you. – MulletDevil Nov 27 '12 at 21:33

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