Vertex Normal
A [see page 13, normal] is a vector that is perpendicular to the 'underlying' surface at that point.
They are used to add depth (facing outward or inward) related information to a
mesh.
This is divided into 2 kinds of normals. The vertex normal is applied to each vertex in a mesh, whereas a polygon normal is applied only at the center of a polygon.
The way to calculate a normal varies from [see page 14, shape to shape] and for [see page 15, arbitrary polygons]. All normals have to be normalized into NDC.
A [see page 16, [vertex normal](COM3503-w02-polygon-meshes)] (that approximates the curvature of the underlying smooth surface
approximated by the polygons) can be calculated by **averaging the the surrounding
polygon normals**.