facet normal
Technical term in 3D computer graphics; a vector perpendicular to a polygon facet, used for lighting calculations.
Facet normals for each face are needed for shading calculations in a 3D model.
法線 is a general term for a normal line or vector, while 小面法線 specifically refers to the normal of a small polygonal facet in computer graphics.
Compound of 小面 (small face/facet) and 法線 (normal line), a direct translation of the English term 'facet normal'.