In article <39252E36.172E8698@my-dejanews.com>, 
gre### [at] my-dejanewscom wrote:

> How would one designate (in isosurface lingo):
> 
> 1)  a plane at y=1.000 with its normal 'up'
> 2)  a plane at y=0.999 with its normal 'down'
> 
> There's some kind of terminology like (y-.00001), but I've been unable
> to figure it out........

function {y} will make a finite(bounded by the contained_by object) 
plane at y=0 with a +y normal. "-y" will flip it upside down(as would 
"sign -1" in the isosurface block outside the function, "inverse" could 
also do the job).
Subtracting a number from y will move the plane +y, adding one will move 
it -y, but you have to be careful of the signs when using -y. I suggest 
you use "-(y-Dist)" or something similar...

Also, the full equation for a plane would be something like:
function {x*a + y*b + z*c - Dist}
where a, b, and c are the coordinates for the normal, and Dist is the 
distance from the origin.

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/

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