A face is a planar area in 3D space. The planar structure can be a polygon, an ellipse, or a donut (Area).

The orientation of a face is determined by using the following rule: If the fingers of your right hand curl along the order of the vertices, the direction that the thumb points to is the front of the face. This thumb direction also describes the surface normal of the face, a vector that points outwards perpendicular from the area.

While a face is often expected to be planar, FME does not enforce planar restrictions in the storage of faces. If required, transformers may be used to force faces into more strict adherence of planar constraints.

Optionally, faces may possess a transformation matrix. Faces may also possess front or back appearances, and may be single or double sided.