Wasn't it EricG who wrote:
>I have been playing with functions in isosurfaces lately.  The attached picture
>shows what amounts to a damped cosine wave overlayed on a hexagonal plate.  The
>first image is the basic isosurface.  Note the peak in the center.
>
>For the second image, I used a cylinder to cut a hole in the center of the
>isosurface using a difference operation.  Note the "ghost" of the peak
>appearing in the image.
>
>For the third image, I added a mostly transparent view of the cutting cylinder
>as a separate object to visualize and ensure the cylinder was the right size,
>etc.  Note that the "ghost" has disappeared in this image.  The only difference
>between second and third images is the addition of the view of the cylinder.
>
>Question:  what is causing the "ghost" of the peak of the isosurface (the part
>cut out by the difference operation?

Odd things can happen with isosurface CSG operations if you don't set 
max_trace high enough.

-- 
Mike Williams
Gentleman of Leisure

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