Fig. 4From: Semi-automatic measurements of foot morphological parameters from 3D plantar foot scansFirst derivative analysis of the plantar foot surface. For one foot of one subject, slope of the plantar surface in three planes parallel to the YZ plane. A threshold of the first derivative dy/dz = 1.7 (i.e. 60 deg slope) was used to identify and separate the plantar surface region from the foot sidesBack to article page