# Build a view frustum from angles

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 http://docs.unity3d.com/Documentation/ScriptReference/Camera-projectionMatrix.html I tried doing `(near plane-far plane) * Tan(angle)` But that didn't give the correct results.

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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.

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