View Full Version : Math perspective question

Master Lolo
12-20-2001, 07:41 AM
Hi, I have a very simple math question I can't handle :

I specify my camera perspective by using
gluPerspective(fov, ratio, front, back) ;

I want to get the widht and height of my front plane using only fov, ratio, front and back, as you cans specify in a glFrustum call.

This is to perform view frustum culling using bounding spheres.

Thx in advance


12-20-2001, 08:16 AM
Is this not a trigonometry question? I could be wrong but I thought I'd have a go cos I need the practice http://www.opengl.org/discussion_boards/ubb/smile.gif

I think height = sin(fov/2) * near

not so sure about the width, still thinking about it, but could someone confirm the height for me please?

12-20-2001, 08:22 AM
width = aspect * height,

but I'm less confident of this one, so if someone could check it...

Master Lolo
12-20-2001, 08:35 AM
I found by myself, here it is :

Width = Front * tan(Fov/2)
and Height = Width / Ratio

thx endo http://www.opengl.org/discussion_boards/ubb/smile.gif

12-20-2001, 08:52 AM
Is that the same as mine? btw, I thought the fov was in the vertical axis, is that right?

Master Lolo
12-20-2001, 09:05 AM
I consider it being in the X axis so that's why tan and no sin

Master Lolo
12-20-2001, 09:06 AM
huh but you seem to be right, Red book says it's fovy... I need to change my code then http://www.opengl.org/discussion_boards/ubb/smile.gif

Maybe simply switching Height and Width would do I bet