question: public static Plane constructNormalizedYPlane ( final double x , final double z , final double DValue ) { if ( Math . abs ( x ) < MINIMUM_RESOLUTION && Math . abs ( z ) < MINIMUM_RESOLUTION ) return null ; final double denom = 1.0 / Math . sqrt ( x * x + z * z ) ; return new Plane ( z * denom , 0.0 , - x * denom , DValue ) ; }
target:  Construct a normalized plane through an x-z point and parallel to the Y axis. If the x-z point is at (0,0), return null.