# Surface normal directions - Manual do Geomview
Manual do Geomview

#### 4.1.5 Surface normal directions

Geomview uses normal vectors to determine how an objeto is shaded. The direction of the normal is significant in this calculation.

When normals are supplied with an objeto, the direction of the normal is determined by the data given.

When normals are not supplied with the objeto, Geomview computes normal vectors automatically; in this case normals point toward the side from which the vertices appear in counterclockwise order.

On parametric surfaces (Bezier patches), the normal at point P(u,v) is in the direction dP/du cross dP/dv.