Stefan Viljoen <rylan@ nous apporta ses lumieres ainsi en ce 2004/05/15 
04:00... :

>Hi guys
>
>I am fairly new to PovRay and I have ran into some issues - wonder if you
>can help?
>
>1. What is a common trace time for complex images (lots of reflection /
>refraction, many objects)
>
>I realise this is subjective, but I have reasonably simple scenes (10 000
>objects, and about 30 reflective/refractive objects, ten light sources)
>that take literally weeks to render while various IRTC entries I have seen,
>with scenes literally thousands of times more complex (as regards APPARENT
>objects and reflections / refractions) done with PovRay, render in times of
>2 or 4 hours. So IS two weeks tracetime (or even a month) for a 1152x864
>image acceptable, or am I doing something exceedingly stupid? Or is this so
>subjective its not worth an answer? I am referring to times on a
>"standard"-ish system - P4 2.0 GHz with 512MB on Rh9 Linux, the raytrace
>being the only user process running.
>
>Is there anybody else out there with such long tracetimes? How did you
>reduce them without losing scene quality?
>  
>
Each light increase significantly the render time. Sometimes, you can 
reduce the number of light by using a shadowless light or by changing 
the ambient value. If a light only affect a small part of your scene, 
make it a spot light. Features like focal_blur, photons and radiosity 
increase render time. Turn off the first two for the test renders. For 
small, distent or partly occulted object, use lower settings, simpler 
textures, normal instead of iso_surface.

><snip>
>4. Pointers / hints?
>
>Any URL's or info on PovRay optimisation? I have often looked for
>optimisation guides for programming, but are there any for the PovRay scene
>language?
>  
>
Using isosurfaces? Try using tighter bounding shapes. Fine tune 
max_gradient to make it as small as possible. Having a cylindrical or 
spherical iso? Try to replace it with a similarly looking lathe or sor.
If you have intersection or difference of very large or infinite 
primitives, use manual bounding.

>5. Reasons for scanline renderers being faster - is scanline better?
>
>I have seen images created with 3DStudio that would (I think) take YEARS to
>render with PovRay. Which technique is better, i. e. which program is
>better - a scanline renderer (what does that mean? What is the difference
>between that and raytracing?) or a raytracer? I have heard about IPAS
>modules for 3DStudio that do raytracing - so 3DS can do both? Why is
>scanline so very much faster than raytracing, but looks just as good?
>  
>
Scanline use shortcuts, hardware acceleration, use 
prerendered/precalculated elements, use fake reflections, usualy don't 
bother with refraction (I saw one (1) exeption). Fast and dirty.

>Anyway, thanks for your time!
>
>Regards,
>
Alain

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