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