Wasn't it Mike Thorn who wrote:
>
>Speaking of bounding, I've heard that POV's bounding isn't always as 
>efficient as it could be. Would it be worth my while to manually bound 
>every object in my scene, or would it be too much trouble for minimal gain?

Most of the time POV's bounding is extremely good. For single objects,
unions and merges it's far more likely that you'll make things go slower
if you try to apply manual bounds. There are a handful of specific
situations where POV can't calculate reasonable bounds. The most
significant of these are things like those covered in my holes tutorial,
but note that you can't fix these situations by just manually bounding
the objects.

POV isn't able to sensibly bound shapes created by intersecting planes,
like the Tetrahedron in shapes2.inc, so the included declaration of
Tetrahedron contains a manual bound. POV doesn't apply bounds to
infinite planes, and doesn't manage to spot situations where an
intersection of infinite planes creates a finite object.

POV automatic bounding is limited to slabs (i.e. box shapes which are
limited to being aligned with the axes) so there may be some situations
where a long thin rotated bounding box might fit an awful lot better
than such a fat orthogonal slab. 

If you suspect that POV is applying poor bounds to something in your
scene you can always display the vista buffers by putting +UD in the
command line. Vista buffers are 2d squares in the image plane that are
drawn round the bounding slabs. (Hint: if there are less than three
objects in the scene you are testing, also add +MB0 to the command
line.)

-- 
Mike Williams
Gentleman of Leisure

Post a reply to this message

>>Speaking of bounding, I've heard that POV's bounding isn't always as 
>>efficient as it could be. Would it be worth my while to manually bound 
>>every object in my scene, or would it be too much trouble for minimal gain?
> 
> 
>   It depends on the object.
>   Certain objects are difficult to bound automatically, although most of
> them can be done so.
> 
>   If I'm not completely mistaken, min_extent() and max_extent() return
> the coordinates of the bounding box of the object. You can use them
> to visualize where the bounding box really is.

Not forgetting the [easier to turn on but somewhat less useful] "show 
bounds" option...

Typically, POV seems to make a pretty good job of things. I have a habit 
of making polyhedrons out of infinite planes - this is a somewhat 
pathelogical case. If you were to (say) take the intersection of two 
huge spheres that only just touch (creating a "lense" shape), that might 
be slightly sub-optimal. (But not as bad as you might think...)

Andrew.

Post a reply to this message