T.M. Schnieders et al., "Analysis of Variance in Neutral Gaze Head Orientation During 3D Head Anthropometry Data Collection", Proc. of 3DBODY.TECH 2023 - 14th Int. Conf. and Exh. on 3D Body Scanning and Processing Technologies, Lugano, Switzerland, 17-18 Oct. 2023, #22, https://doi.org/10.15221/23.22.

Title:

Analysis of Variance in Neutral Gaze Head Orientation During 3D Head Anthropometry Data Collection

Authors:

Thomas M. SCHNIEDERS, Karen BREDENKAMP, Maral DANESHYAN

Magic Leap, Plantation FL, USA

Abstract:

The Frankfurt plane head orientation is widely used in anthropometry research and anthropometric measurement definitions of the whole body and head. However, the authors believe that this head orientation may not be the best for head mounted extended reality (augmented, virtual and mixed reality) devices since it does not relate to natural product wear. When designing head mounted devices (HMDs), it is important to define head orientation, specifically pitch, related to how the device will be worn. In particular, these HMDs are often designed around the eye position with the head and eye in a natural, relaxed orientation - defined in this paper as the "Neutral gaze". However, the efficacy and repeatability of collecting this posture has not been thoroughly studied. The purpose of this study was to assess the variance of a repeated measures neutral gaze protocol. The primary research questions were: (1) What is the variance in neutral gaze within and between subjects, and (2) what are the largest sources of variance/error? Twelve subjects (four females, eight male) participated in this study. The data collection protocol was repeated five times per subject. Three anatomical landmarks were selected for their resistance to incorrect land marking and measurement - the Left and Right Tragion and the Sellion. Subjects were landmarked, performed a defined series of neck and shoulder stretches, and had their head scanned using a 3dMD head scanner. Following each scan, subjects stood up, walked up three sets of stairs, performed neck and shoulder stretches, returned to the scanning room, performed neck and shoulder stretches, and an additional head scan was taken. Head scans were digitized in 3dMD Vultus® providing coordinate point locations for the anatomical landmarks under study. This digitization process was conducted three times with proctor A and three times with proctor B to be able to assess intra- and inter-rater reliability. A "Neutral Gaze Vector System" was defined as a user-specified system, where the origin was defined as a point 3 mm in front of the Pupils at the midpoint between the Right and Left Pupil, the x-axis runs through the Right and Left Pupil, the y-axis runs vertically upwards, and the z-axis runs in the anterior direction. MATLAB was used to align all heads to this coordinate system. Variance and range for head pitch were calculated. The authors hypothesized five primary sources of variance: (1) anthropometry land marking, (2) position error of the participant, (3) scanning resolution at the pupil, (4) digitization error, (5) inter- and intra-rater reliability, and (6) MATLAB rotation/translation. Three of these five were investigated in this study. The results indicated the biggest sources of error to be: (1) positioning of the subjects and (2) digitization errors. The result of this work verifies the accuracy and repeatability of the neutral gaze protocol for a product related head orientation. This is especially important when performing such tasks as evaluating form and fit of subjects wearing head mounted devices.

Keywords:

3D face scanning method; method validation; neutral gaze; head orientation; head mounted displays

Details/PDF/VIDEO:

Full paper: PDF
Presentation: VIDEO
Proceedings: 3DBODY.TECH 2023, 17-18 Oct. 2023, Lugano, Switzerland
Paper id#: 22
DOI: 10.15221/23.22

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