On 10/22/2014 04:10 AM, fuglede wrote:
> So, problem #1: as you can see from final structure, even though the entire
> thing consists of a bunch of vertical translates, the "middle" set of ramps has
> some issues with lighting (the checker pigment is all smeared). I found that I
> could limit this effect by giving lower values of accuracy, but if I go below
> 0.000007, I'll get a segmentation fault when rendering. Here's a still showing
> the problem:
>    https://i.imgur.com/p7ZkDTZ.png
>
> Is there any way around this issue?
>
> My second problem is probably related. If I try to double the angle of the
> slices (i.e. change Angle to 8/360*2*pi in the code below), some translates
> behave weirdly. Again, here's a still:
>    https://i.imgur.com/cDYNLHD.png
> As you can see, the topmost ramps have some strange cuts that the bottommost do
> not, even though they're all just translates of the same thing. Is there any way
> to fix that?
>

I don't have a lot of experience with parametric surfaces, but I've 
found with them and some other of Pov-Ray's mathematical surfaces that 
there can be issues when the rays from the camera more or less line up 
on the axis of the mathematical axis there can be noise. I've seen this 
in more complex prisms too for example.

Looks like your camera is offset some so a quick test as to whether you 
are hitting calculation noise is to try an orthographic camera by adding 
the word orhographic as the first line of your camera definition. You 
probably won't want this camera type for your final render, but if it 
cleans things up, it gives the strong hint cleaner results are possible 
by positioning your camera more off axis relative to the problem parts 
of the object. If orthographic works, with the default camera maybe go 
to a height of 1.5*height in z. Or a change to the parametric object 
itself might help if it makes the problem camera ray to object 
relationship less orthogonal.

Other things I see. You've got a couple pigment+finish definitions on 
sub objects of the whole. This can be done if one is careful not to 
create competition between them. It would be more normal to have one 
texture in the final union/object.

Parametric objects are defined by their surface so where doing 
differences or intersections on the edge you may well have black or 
white spots which are difficult or impossible to eliminate.

With all numerical noise issues, anti-aliasing, +A, +jitter etc, can 
help quite a bit, but the noise too can make the anti-aliasing more 
expensive.

I couldn't really see the issue with the smaller angle - the differences 
looked to me to mostly due looking at aspects of the surface. Maybe 
there were some of the 0-thickness edge effects opening things up a 
little - I was not sure. Also possible I am not seeing that issue.

Hope something in my rambling a help.

Bill P.

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