That's pretty much exactly what it does! I have a macro already, the only 
limitation of it is that it doesn't look for the steepest slope, just any 
downward slope. Nonetheless this does mean that it definitely doesn't flow 
up hill at any point.

Could someone point out the bits where it looks wrong? Honestly I can't see 
it!

-- 
Tek
http://evilsuperbrain.com

"David El Tom" <dav### [at] t-onlinede> wrote in message 
news:43e466a7@news.povray.org...
> Christoph Hormann wrote:
>> St. wrote:
>>>
>>>    I'm having a job to see where it's flowing uphill?
>>>
>>
>> When i say "it should always flow downhill" this does not necessarily 
>> mean it flows uphill in the image (although i am sure it does in some 
>> places).  It is simply not taking the downhill direction everywhere (i.e. 
>> the *steepest* direction going down).
>>
>> Christoph
>>
>
> should be not to hard to code a macro to trace a path with steepest 
> descent.
>
> (some kind of local monte carlo approach, similar to the methods used to 
> find local minima of multi-dimensional hypersurfaces)
>
>  - store the altitude of the current position
>  - step forward
>  - shoot rays in random fashion around the new position and trace the 
> altitudes (the more you shoot the greater is the possibility to find the 
> local steepest descent for this point)
>  - compare thoose with the stored one and alter direction to the one with 
> biggest difference
>  - store this point as new position.
>
> if you would store the gradient at each point you could use it reciprocal 
> factor for the broadness of the lava flow, as it shoud get thighter if it 
> flows faster and broader if it flows slower (constant flow rate).
>
> another possibilty is to use the analytical derivative of the function you 
> use for the volcano surface.

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