William F Pokorny <ano### [at] anonymousorg> wrote:
> On 10/1/19 10:18 AM, IGM wrote:
> > Your comment about ray subdivision and stepping led me to think of a first
> > approximation to the problem: any object could be subdivided in a certain amount
> > of small volumes (cubes? 3D voronoi cells?), each with different ior; something
> > similar to FEM analysis. With small enough cells, or small enough ior
> > differences, focal_blur could help giving continuity to the whole object. This
> > approach can be done without adding new features to povray. User has the
> > freedom to choose the right cells dimensions (ie.e degree of approximation) for
> > his specific scene.
>
> My mind keeps drifting back to this...
>
> [...]

I realized that this problem is actually extremely complex. I still need
thinking to it and to your suggestions..

> Suppose my initial thought is no, but maybe I don't understand what
> Zemax is really doing with ordering from what you said.

The ordering is not physical, i.e. due to the ray direction/properties: it
simply refers to *the order of the objects in the description of the scene*
(!!). Zemax looks like a spreadsheet: in the list, object 6 defines the
properties eventually ambiguous with object 5 and all the previuos, as in the
case of coincident surfaces. This brutal solution is not physical, but simply
helps the user being consciuos of what's going on, and therefore governing the
system. Taking your example about the juice glass, you can define both solids
(the juice in line 4 and the glass in line 5, we say), and describe the
properties you care (scattering, coatings, and so on..) on the internal surface
of the glass (that is the last object in the description). Any time a ray will
be traced, the software will recognize that, in case of ambiguity, the
properties defined on object in line 5 dominate over those of the previous ones.

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