Variation in proportion indices and angles between selected facial landmarks with rotation in the Frankfort plane

A number of different techniques are employed in facial image comparison of living persons. In this study, the effect of rotation on angles and proportion indices between selected facial landmarks is evaluated as a first step to assess whether facial anthropometry could be usefully applied to facial image comparison. The faces of five volunteers were photographed in the Frankfort plane at different angles of rotation from 0 degree (frontal) to 90 degrees (side view), rotating every 10 degrees both clockwise and counter-clockwise. Four landmarks were used: right and left ectocanthions, nasion, and stomion. The proportion indices of the measurements between these landmarks were calculated as well as the angles created by the lines connecting the same landmarks. The results show a consistent and predictable variation between the five subjects. With rotation, the greatest variation is seen where horizontal landmark connecting lines are combined with the ectocanthion/ stomion lines or nasion/stomion. There is less variation in the proportion indices for vertical and diagonally orientated landmark connecting lines.