POV-Ray : Newsgroups : povray.advanced-users : Mathematical "Primitive" vs Isosurface : Re: Mathematical "Primitive" vs Isosurface Server Time
28 Sep 2021 17:50:22 EDT (-0400)
  Re: Mathematical "Primitive" vs Isosurface  
From: Le Forgeron
Date: 7 Aug 2019 11:47:08
Message: <5d4af27c$1@news.povray.org>
Le 06/08/2019 à 23:05, Bald Eagle a écrit :
> 
> Aside from the obvious user-defined vs implemented in source code,
> 
> can someone define and differentiate the difference between a "mathematical
> primitive" like a
> 
>      sphere {0, 1}
> 
> and an isosurface object such as
> 
>      isosurface {function { x*x + y*y + z*z - 1 }} ?
> 

The generic function need to be evaluated in various points along the
ray/path, to solve the root(s).
No intrinsic knowledge of the properties of the function is used.
The good side is that the evaluation is limited to a container.
The bad side is that bounding box optimisation is only a dream.
The computation of fancy position uses the provided data.
The computation of the function uses a virtual machine, which can be
non-optimal for the native CPU.


The native sphere: we can use its properties.
The maximal number of roots (intersection with a ray) is known.
Computing all the roots for a path is simple, without intermediate
evaluations.
The computation of fancy position uses a translation to reduce the
problem to a sphere at the origin. This might have an impact on native
precision when translated back.
UV-mapping might be available. (from coordinate of intersection to
uv-values)


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