On 08/07/2015 06:14 PM, Samuel Benge wrote:
> scott<sco### [at] scottcom>  wrote:
>>> The attached shows artifacts present at various accuracies for the function
>>> sqrt(x*x+y*y+z*z)-1.>
>>
>> Assuming you've got no pattern displacement in any of those images, it
>> looks to me like it's something to do with the shadow ray being started
>> too close to the surface (and hence the tracer immediately thinks the
>> shadow ray has been blocked by the isosurface itself).
>
> I should have guessed that, since I ran into shadow ray problems last summer
> with the raymarching stuff. The shadow ray's origin had to be spaced from the
> initial hit point (by backing it up toward the camera or outward from the
> surface), or else artifacts would appear.

Question: Does the problem go away if you make the spheres bigger? Like, 
say, 10 units across instead of just 1?

As I recall, POV-Ray tends to dislike rendering either very tiny or very 
large objects. Floating-point precision issues and all.

(Most particularly, I believe the minimum distance for a shadow ray to 
travel is a hard-coded constant, which might be too small if the 
isosurface itself is very tiny.)

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