RE: [Algorithms] View Frustum Culling

[Tom F. <to...@mu...>]

Plain text please - some people here are on non-HTML systems.

I reckon that "either" is a good answer, as long as you first cull by the
bounding sphere, which is slightly bigger (OK, a lot bigger in some cases)
but usually much faster.

So, cull by the bounding sphere, and that spots 90% of the cull cases. So
the remaining 10% are the ones you need to use AABB/OBB to spot.

And using hierarchial volumes also helps enormously on applicable shapes -
and you should probably do sphere-testing all the way down to the nodes
themselves before trying anything fancier, i.e. never do AABB/OBB testing on
a non-leaf. Much quicker in most cases to just recurse down & sphere-test
the kids.

Tom Forsyth - Muckyfoot bloke.
Whizzing and pasting and pooting through the day. 

-----Original Message-----
From: Tim Johnston [mailto:ti...@gn...]
Sent: 07 September 2000 11:50
To: gda...@li...
Subject: [Algorithms] View Frustum Culling


 
What is the best method for coarse bounding box frustum culling?
 
From what I can gather you either use axis aligned bound boxes (AABBs) or
oriented bounding boxes (OBBs), with OBBs having the advantage of tighter
fitting but need extra computations for the culling process. Also which
culling method is best, perspective transform the BB and the view frustum to
the perspective coordinate system (which with AABBs can result in testing
two AABBs which is just 6 comparisons, however you have to transform all 8
vertices of the AABB) or testing the BB against the 6 planes of the view
frustum (which seems much simpler and straightforward if that is all that is
needed.)
 
So is comparing AABBs against the frustum planes the best way to go and is
it just find the equations and test the vertices or is there some more
transforming needed in there?
 
Also what are the extra steps needed to use OBBs instead?
 
And finally a nice easy question, what is the right way to get the 6
equations of the planes if you happen to have an OpenGL matrix?
 
Any help would be great
thanks,
 
Tim.