  Geometric conditions on general polygons are given in [9] in order to
guarantee the error estimate for interpolants built from generalized
barycentric coordinates, and the question about identifying sharp geometric
restrictions in this setting is proposed. In this work, we address the question
when the construction is made by using Wachspress coordinates. We basically
show that the imposed conditions: bounded aspect ratio property (barp), maximum
angle condition (MAC) and minimum edge length property (melp) are actually
equivalent to [MAC,melp], and if any of these conditions is not satisfied, then
there is no guarantee that the error estimate is valid. In this sense, MAC and
melp can be regarded as sharp geometric requirements in the Wachspress
interpolation error estimate.
