In thegeometry ofcomputer graphics, avertex normal at avertex of apolyhedron is a directional vector associated with a vertex, intended as a replacement to the true geometricnormal of the surface. Commonly, it is computed as thenormalized average of thesurface normals of thefaces that contain that vertex.[1][2] Theaverage can be weighted for example by the area of the face or it can be unweighted.[3][4] Vertex normals can also be computed for polygonal approximations to surfaces such asNURBS, or specified explicitly for artistic purposes. Vertex normals are used inGouraud shading,Phong shading and otherlighting models. Using vertex normals, much smoother shading thanflat shading can be achieved; however, without some modifications to topology such as support loops, it cannot produce a sharper edge.[5]
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