An in-vivo study on the effect of head orientation in the measurement of anthropometric points in stereophotogrammetry.

Background: It is well known that in bidimensional photography the orientation of the head is fundamental to obtain a correct reproduction of the subject. Even minimal errors in yaw, roll and pitch of the head can be cause of unreliability of the photography itself. This is not the case in three-dimensional photography in which head positioning may have no influence on the reliability of the results since on the computer the 3D reconstruction of the face can be oriented as desired, allowing any small errors to be corrected. The authors, in a previous in-vitro study, demonstrated this using a mannequin of the head. In the present study, the Authors repeat the study in vivo to verify any differences.

Methods: Seventeen anthropometric points were marked on the face of a young adult female (26 years old) with eyeliner. Images of the face were then acquired with a stereo-photogrammetric system (Face Shape 3D MaxiLine) in natural head position and with varying degrees of roll, pitch and yaw. The anthropometric points marked on the skin were then recognized and marked on a digital software (Viewbox, dHAL Software, 6 Menandrou Street, Kifissia 14561, Greece) on each individual image. 14 linear distances between these points were measured using the same software.

Results: The linear distances of these points in the stereophotos taken at centered positions were then compared with those taken with different degrees of roll, pitch and yaw. This study confirms previous results obtained in vitro regarding the presence of areas of non-equivalence (P<0.05) when comparing the frontal and lateral regions of the face at various angles.

Conclusions: However, it introduces important suggestions on the collection of data from specific anthropometric points. If these points are to be assessed, the medical staff will have to take special precautions to obtain reliable images.