Fig. 3. FE model and surface approximation. a, Surface reconstruction with three approximation methods based on nine tracked nodes, indicated as one blue triangle (fixed nodes) and eight red circles (free nodes). The displacement errors of piecewise bilinear interpolation, triangle-based non-linear interpolation and FE-based data enrichment are color-coded with blue indicating a smaller error. b, Fiber strain responses of five deformation patterns in FE simulation, where warmer colors indicate a higher induced strain.