Surface normal directions - Geomview Manual
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#### 4.1.5 Surface normal directions

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

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

When normals are not supplied with the object, 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.