Directional Smoothing

'Directional smooth' is a check box just below regular smoothing. 

Directional smoothing causes the smoothing effect to be stronger in a particular direction and weaker in the perpendicular direction.

Enter the primary smoothing direction in the provided text box.

'Smoothing strength in the primary direction' allows you to set the influence radius in that direction.

'Smoothing strength in the secondary direction' controls the influence radius at a 90 degree angle to the primary direction.