Automatic Detection and Reproduction of Natural Head Position in Stereo-Photogrammetry.

Tai-Chiu Hsung,John Lo,Lim-Kwong Cheung,Tik-Shun Li

doi:10.1371/journal.pone.0130877

Abstract

The aim of this study was to develop an automatic orientation calibration and reproduction method for recording the natural head position (NHP) in stereo-photogrammetry (SP). A board was used as the physical reference carrier for true verticals and NHP alignment mirror orientation. Orientation axes were detected and saved from the digital mesh model of the board. They were used for correcting the pitch, roll and yaw angles of the subsequent captures of patients’ facial surfaces, which were obtained without any markings or sensors attached onto the patient. We tested the proposed method on two commercial active (3dMD) and passive (DI3D) SP devices. The reliability of the pitch, roll and yaw for the board placement were within ±0.039904°, ±0.081623°, and ±0.062320°; where standard deviations were 0.020234°, 0.045645° and 0.027211° respectively. Conclusion: Orientation-calibrated stereo-photogrammetry is the most accurate method (angulation deviation within ±0.1°) reported for complete NHP recording with insignificant clinical error.

Highlights

A new method for recording Natural head position (NHP) [1,2,3,4,5,6,7,8,9,10] in stereo-photogrammetry (SP) was suggested [11]
The idea was to use the physical references of a pre-captured digital model of a board to correct the orientation of subsequent facial surface models
The achieved overall accuracy of physical references derived from the board [11], to the axes defined by gravity and mirror orientations, was within ±0.2°; where standard deviation was around 0.11°

Summary

Introduction

A new method for recording Natural head position (NHP) [1,2,3,4,5,6,7,8,9,10] in stereo-photogrammetry (SP) was suggested [11]. The idea was to use the physical references of a pre-captured digital model of a board to correct the orientation of subsequent facial surface models. The achieved overall accuracy of physical references derived from the board [11], to the axes defined by gravity and mirror orientations, was within ±0.2°; where standard deviation was around 0.11°. These were considered to be clinically insignificant. The stereophotogrammetric NHP method possesses many unique advantages over traditional approaches: 1) radiation-free; 2) patients can be in their own NHP for capturing of facial surface models without the need for any markers/sensors; 3) only one reference board recording is PLOS ONE | DOI:10.1371/journal.pone.0130877. The stereophotogrammetric NHP method possesses many unique advantages over traditional approaches: 1) radiation-free; 2) patients can be in their own NHP for capturing of facial surface models without the need for any markers/sensors; 3) only one reference board recording is PLOS ONE | DOI:10.1371/journal.pone.0130877 June 30, 2015

Objectives

Methods

Discussion

Conclusion