POV-Ray : Newsgroups : povray.binaries.images : trace() is unreliable on lathe : Re: trace() is unreliable on lathe Server Time
28 May 2022 00:44:30 EDT (-0400)
  Re: trace() is unreliable on lathe  
From: Kenneth
Date: 27 Apr 2022 13:35:00
Message: <web.62697ddb34e735428d86850a6e066e29@news.povray.org>
[in v3.8.0 beta 1  Windows 10]

I ran your 14-frame animation over and over again, changing the 'Offset' from
0.0 by 0.0001 increments. On my system, the trace mistakes you mentioned finally
disappear at 0.0029. Strangely, there were instances where trace succeeded
completely, then the next increment would re-introduce them!

The use of sturm or no-sturm didn't seem to make a difference.

With Offset at 0.0, I also tried slightly rotating your 'form' objects (in all
three axes)-- like  rotate 1 -- which again eliminated the trace mistakes. But
that's probably identical to using Offsets.

I would guess that there are mathematical inconsistencies (creating possible
holes in the shapes?) below a certain precision level...or that a strict x/y/z
tracing direction somehow interacts badly with the precision of the troublesome

As a more general question, is it necessary to trace the objects strictly along
the x/y/z axes? In other words, would a random (OR ordered) series of trace
operations-- originating from a 'sphere' outside the object and all directed
toward <0,0,0> -- suit your purpose instead? Although, I suppose any indents in
the shapes would present a problem with that scheme.

Ideally, I would imagine that each trace direction needs to be aligned toward
the normal of the shape at each point-- but that would require a preliminary
trace operation to find the normal there!

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