In article <mat### [at] netplexaussieorg>,
 Matthew Pace <mat### [at] lycoscom> wrote:

> Last time I asked a isosurface question, it was a stupid error on my 
> part, and thats what I get for coding too late at nite...  This time, 
> though, I am really confused.  IF (IF) I understand isosurfaced 
> correctly here, (tell me if Im wrong), POV checks to see which parts of 
> the containing box fit into the function to equal the threshold.  if 
> this is true, take the following scene:

I don't really understand your explanation of what you think happens, so 
I will just explain what happens. ;-)
An isosurface is a surface composed of all points where a function is 
equal to a certain threshold value. All points where that function is 
less than the threshold are considered "inside" the isosurface. Because 
of computational constraints, the isosurface shape in POV-Ray limits 
isosurfaces to within a container shape. By default, if a part of the 
container is inside the isosurface, it is considered part of the 
surface. Using the "open" keyword will remove these container surfaces, 
giving you holes into the interior of the isosurface where it intersects 
its container.


> 1) Wouldnt just a plane show up?  y equals 0 on only one plane, doesnt 
> it?

A plane and all parts of the container where the function is less than 
the threshold.


> 2) If y is negative, why is the positive part of the sphere shaded?

By "shaded" I assume you mean present...and the +y half of the container 
is visible because -y is below the threshold for those points.
Hope this helped...

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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