Christoph Hormann wrote:
> Wolfgang Wieser wrote:
>> [...]
>> 
>>>which will work
>>>well in cases like these where the accuracy is much smaller than the
>>>features of the isosurface function anyway
>>>
>> 
>> This is correct. If you really want the _isosurface_ of a function to get
>> plottet in a numerically usable way, you need to have
>> "accuracy" < "characteristic surface feature grain size".
> 
> Your numbers what factor you can reduce the accuracy settings are quite
> wild guesses.  It depends on how well the linear interpolation
> approximates the real change of the function in the final interval.  
>
This is certainly correct. That's why I put the "well-behaved" in there :)
It turns out that the "wild guesses" are fulfilled quite good for smooth 

if one is rendering the Mars topography since the function in question 
is a linearly interpolated image map itself. 

> If 
> it does this badly you won't have such a gain (factor 10 would already
> be extremely good).  
>
Yes. But OTOH it is _very_ unlikely to get below factor 2. 
(And actually no reason not to use it.)

> Also note the normal vector calculation uses the 
> accuracy value as well so by increasing the accuracy setting you also
> influence the calculation of the normal vector.
> 
Yes, I saw that because my initial guess for the reson of the black dots 
was problems in the numerical differentiaion. And actually, numerical 
diff is one of the most critical things. There simply isn't a perfect 
solution for the problem -- especially no cheap one. 

> Sure, some time.
> 
Well... "some time"... 
Do you mean I need to code it myself if I want functionality like that 
this year?

Wolfgang

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