Samuel Benge wrote:
> 
> Okay, the example image has been uploaded to p.b.i. I gave three 
> examples in png format, each one having a different accuracy value. 
> Also, the isosurface has smooth and rough surfaces combined for obvious 
> reasons. The code for the example is below. You might want to uncomment 
> the max_gradient and use very high values, to conclude the artifacts 
> shown are not related to max_gradient. Also, I encourage both you and 
> Wolgang to try this in the patched version. I'd like to see the results.
> 

What you see on the front face of the box are exactly the explained 
shadow ray noise effects you also see on Wolfgang's samples caused by 
tangential lighting.  The surface is always found reliably, just if it 
is in shadow or not varies.  Since these surfaces result from a 
precisely linear function the linear interpolation leads to perfect 
results here for arbitrary accuracy values (on the faces, not near the 
edges and only within the accuracy of floating point numbers of course).

Since you usually won't use tangential lighting in real scenes for such 
flat surfaces i moved the light source a bit.  I also changed 
max_gradient to 4 (the real maximum gradient of the function seems just 
above 3).  Here are the results:

no interpolation:

http://www.tu-bs.de/~y0013390/files/sam_test1_o05.png
http://www.tu-bs.de/~y0013390/files/sam_test1_o01.png
http://www.tu-bs.de/~y0013390/files/sam_test1_o001.png

with Wolfgang's patch:

http://www.tu-bs.de/~y0013390/files/sam_test1_i05.png
http://www.tu-bs.de/~y0013390/files/sam_test1_i01.png
http://www.tu-bs.de/~y0013390/files/sam_test1_i001.png

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 06 Jul. 2004 _____./\/^>_*_<^\/\.______

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