Fig 2.

Standard representation of the calvaria. (a) Right lateral view of the cranial bones of an example subject together with the cranial base landmarks represented as white spheres. (b) Representation of the spherical sampling of the external surface of the calvaria in the Euclidean space. The X axis is aligned with the left-to-right direction, the Y axis with the posterior-to-anterior-direction and the Z axis with the inferior-to-superior direction. (c) Representation of the elevation (α) and azimuth (β) angles in the bone labeling spherical map of the subject in (a). The landmarks at the glabella (top) and opisthion (bottom) are shown as purple circles for reference. (d) Three maps of the sampled Euclidean coordinates (X, Z and Y coordinates, from back to front) of the surface of the calvaria, together with a representation of the control point defining the radial basis functions as green circles. (e) Reconstruction of the external surface of the calvaria from the spherical maps in (d) using radial basis functions. The original base of the cranium for this patient is represented in white for reference.