In article <38a9a1b2@news.povray.org>, "David Vincent-Jones" 
<geo### [at] galaxynetcom> wrote:

> I am working on a project with a very large geographical span.
> This entails a huge height_model and a thousand or more objects.
...
> The bounding option does not appear to really help

Have you tried bounding in a tree-like structure? Like, if you have a 
line of 8 objects, bound each half of it separately, and subdivide each 
half of it...ok, I am just really bad at explaining this. If you know 
something about programming, it is similar to a binary search tree.
If you do this, make sure you change the settings so POV doesn't ignore 
your bounded_by statements.


> and I am interested to explore the possibility of using the inside of 
> a reduced radius sky_sphere to lop off part of the scene.

A sky_sphere is not an object, it just acts like a background with a 
pigment that would fit on a unit-sized sphere. It would be useless as a 
bounding object, but from your description, you appear to be using a 
sphere object instead of sky_sphere.


> I have tried to translate a simple sphere along with the camera 
> position but the time has not really improved enough to make a 
> substantial difference.

Are you translating a bounding shape for all of your objects along with 
the camera? If so, you are not likely to get any increase in speed, in 
fact your render time will probably increase. Bounding works this way: 
if a ray hits the bounding shape defined by bounded_by, it is then 
tested for the bounded shape. There is no requirement that the 
bounded_by shape encloses the shape being bounded. If the bounded_by 
shape surrounds the camera, it will always be hit, so the calculations 
for the bounded shape will always be done.

If you are simply moving the sphere you are using as the sky along with 
the camera, so that most of the scene isn't visible...I don't know. That 
might work, but I am not certain how objects in front of other objects 
are handled, I never even looked at that part of the code.

What you might want to do is a kind of "level of detail". If an object 
is a certain distance from the camera, use a simpler model and faster 
textures, or eliminate it completely. An easy way to get the distance is 
vlength(ObjectDistance - CameraPosition).

-- 
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/

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