Normally you wouldn't need it, but POV-Ray describes a plane a bit
differently and normal geometry would. In POV-Ray, D is the minimum
distance from the origin to the plane. It is envsioned by going D units
along the normal vector of the plane <A,B,C> and putting the plane there

In normal mathematical circumstance, D is not the mininum distance from
the origin to the plane, it has a different meaning.
For instance, mathematically, if you have a plane with normal vector
<1,1,2> and it goes through point <2,1,3>, it satisfies the equation 1*2 +
1*1 + 2*3 = D, so D= 9.
In POV-Ray, the same plane would have the same normal vector, but the
disatance from the plane is less than 9.

Josh

Remco Poelstra wrote:

> Hi,
>
> I was reading the manual about planes, and I saw that povray uses the
> equitation: A*x + B*y + C*z = D*sqrt(sqr(A) + sqr(B) + sqr(C))
> Now I was wondering, why that sqrt(sqr(A) + sqr(B) + sqr(C))? Isn't it
> enough to have A*x + B*y + C*z = D?
>
> Remco Poelstra

--
Josh English -- Lexiphanic Lethomaniac
eng### [at] spiritonecom
The POV-Ray Cyclopedia http://www.spiritone.com/~english/cyclopedia/

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