Figure 2:

Illustration of the window function $\left(\frac{\Vert x-c_I\Vert }{d_{\text{ref}}\varrho }\right)$ assuming that the points x and c_I lie on a plane and d_ref ϱ = 1. Control points that are close to x influence the approximation of the material parameter more than points that are further away. Control points that lie at a distance larger than d_ref ϱ do not influence the approximation at x.