title: Automatic Detection and Reproduction of Natural Head Position in Stereo-Photogrammetry.
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.
  
  
  CONCLUSIONS
  Orientation-calibrated stereo-photogrammetry is the most accurate method (angulation deviation within ±0.1°) reported for complete NHP recording with insignificant clinical error.
authors.affiliation: Discipline of Oral and Maxillofacial Surgery, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Tai-Chiu
authors.initials: TC
authors.lastname: Hsung
authors.affiliation: Discipline of Oral and Maxillofacial Surgery, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: John
authors.initials: J
authors.lastname: Lo
authors.affiliation: Discipline of Oral and Maxillofacial Surgery, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Tik-Shun
authors.initials: TS
authors.lastname: Li
authors.affiliation: Discipline of Oral and Maxillofacial Surgery, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Lim-Kwong
authors.initials: LK
authors.lastname: Cheung
mesh_terms: D005145:Face / Q000502:physiology; D006257:Head / Q000502:physiology*; D019416:Head Movements / Q000502:physiology; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D009949:Orientation / Q000502:physiology*; D056888:Patient Positioning / Q000379:methods; D010780:Photogrammetry / Q000379:methods*; D011187:Posture / Q000502:physiology*; D015203:Reproducibility of Results