John Pye nous apporta ses lumieres en ce 07/12/2006 06:45:
> Hi all

> I have an application for POVRAY that seems a little different from what
> most users are doing, and it doesn't seem to be something that's directly
> addressed in the documentation, so I wonder if anyone could offer any
> suggestions.

> I'm trying to assess the imaging properties of a number of reflectors. This
> means that I want to create some geometry for a set of mirrors including
> scattering,  geometric surface imperfections, etc, then I want to create a
> light source in the form of a 'sun shape', then I want to see what the
> resulting light intensity at my target plane becomes.
If you use the various primitives, you have mathematicaly ideal shapes. You can 
simulate imperfections using normals. You can simulate imperfectly polished 
mirrors, or lences, by averaging some normals.

> The normal use of POVRAY seems to revolve around the idea of a 'camera'
> which is a single point 'observer'; Raytracing in this case means tracing
> *backwards* from the eye of the beholder to the different spots in the
> scene.

> My use seems a bit different: I want to have an imaging plane and I want to
> 'catch' rays over that plane. The overall result should be data about the
> intensity of light striking various points on my imaging (target) plane.

> Obviously I can approximate this analysis by creating an imaging plane, and
> then creating a camera that looks at that imaging plane. This won't always
> be practical however, as sometimes the act of creating a visible barrier at
> the imaging plane will cause the optics of the problem to change, eg by
> creating repeated reflections when none are desired.
Add "no_reflection" and "no_shadow". This will effectively create a virtual 
object than will receive any "image" but wont affect light and be invisible in 
any reflection.

> So, can anyone offer any suggestions on how one my start out with using
> POVRAY in this case?

> Finally, is there any way that POVRAY can generate output that shows the
> location of rays in 3-D space? For example if I create a ray-trace any only
> wish to trace a couple of hundred rays, is there any way I can view the
> paths taken by those rays through my scene?
This can be done using some parallel, cylindrical light sources that you can 
colour to enable you to differienciate them. You can also use a mask pierced by 
a collection of holes. It's beter to use a composite mask if you want a large 
number of holes: small boxes pierced by a single hole stacked in an array.
You will also need to add some media so you can see the paths.

> Cheers
> JP
> joh### [at] anuremovethisrubbisheduau

The feature you want is called "photons". It's used for forward tracing of light 
and it's effects. Mike William made an error: photons are NOT usefull for the 
casting of realistic shadows, but for the realistic rendering of caustics 
effects as well as realistic opticaly active objects.

-- 
Alain
-------------------------------------------------
For THIS I bought a computer?

Post a reply to this message