Given two planes:
Π1 : Ax+By+Cz+D=0 and
Π2 : ax+by+cz+d=0
The following uses the notation that
<a,b,c> represents a vector with three components.
The normal vectors are:
N1 : <A,B,C>
N2 : <a,b,c>
If Π1 is perpendicular to Π2, then
If the planes are parallel, we can find a numeric factor α such that
If in addition, D=αd, then the planes are coincident.
If no such α can be found, the planes are not parallel.