and through an isoparametric mapping, the basis functions are defined on irregular polygons.
The Wachspress basis functions and mean value co-ordinates are directly computed on irregular
polygons, which is also the case in a recently proposed non-conforming finite element method
on polyhedral meshes [43]. The interested reader can refer to Reference [40] and the references
therein for further details on the construction and implementation of polygonal interpolants.