Robust ellipsoidal model fitting of human heads

We report current work on methods for robust fitting of ellipsoids to the shape of the human head in three-dimensional models built from laser scanner acquisitions. A starting ellipsoid is obtained from Principal Component Analysis from mesh vertices, those regions far from the surface of the ellipsoid are penalized (outlier rejection and/or damping). A first method consists in re-calculating iteratively the ellipsoid by PCA, adjusting scales. Another method projects the outliers into the ellipsoid. A third method uses a morphological-error approach, via the difference of the distance fields of the head and its fitting ellipsoid. The ellipsoid orientation, position and scales are then changed in search for a set of parameters minimizing the morphological error. To speedup calculations, only a few orthogonal planes are sampled and the distance field is obtained directly from the triangular mesh elements. Among the intended applications, the restoration of the skullcap is presented.