Deriving statistical fit contours and shape of an aerosol mask from 3D head scans

This paper deals with mask shape design to ensure a statistical fit for a given population represented by tessellated 3D head scans. The mask rim curve should contact the face without gaps. This work identifies corresponding points on the mask and facial landmarks. The landmarks define a coordinate frame which helps extract rim contours (mask contours) and facial midline contours (profile contours) from the 3D model. Bilateral symmetrisation procedures are used to correct mild asymmetry in the mask contours. The statistical distribution induced by the contours on a grid is used to derive percentile contour geometries. Mask shapes generated by stacking elliptic cross sections, scaling and convex hull have been explored. 5th, 50th and 85th percentile masks are used for visual fit evaluation on a set of representative faces. The procedure establishes that the landmark-based approach provides a systematic method not only for design but also for fit evaluation.