Invisible wrote:
>> http://www.imagico.de/fast_iso/patch.html
> 
> Tangentally related to the current beta, but... I once though about the 
> isosurface tracing algorithm. If I evaluate the function at a particular 
> point in space and the result is a large positive value, then given that 
> value and the max_gradiant, I know that there can be no surface within a 
> sphere of some radius centered at that point.

POV-Ray already uses this information (slightly different, the exact use 
of this idea is called sphere tracing (see the link list on my page). 
But this is only done on a per-ray basis.  Using it globally would 
require a spatial data structure to store this information for efficient 
access (it would be quite similar to the radiosity irradiance cache and 
would have exactly the same troubles).

The main additional problem would be that the time required for storing 
and querying this information in a lot of cases will exceed the time 
required for an additional function evaluation (in radiosity we store 
the result of tracing 'count' rays for every sample, here it would be 
only the function value).

And note the number of function evaluations (and therefore the resulting 
size of the cache) would be extremely large (easily several billions for 
a large render).

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.imagico.de/ (Last updated 14 Mar. 2006)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

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