3D Gaussian Splatting vs. 2D Photogrammetry and Direct Anthropometry for Facial Measurements

This study evaluates the accuracy and repeatability of 3D Gaussian Splatting (3DGS)-generated 3D facial models by comparing anthropometric measurements derived from these models with those obtained using conventional 2D photogrammetry and direct anthropometry.

In this cross-sectional study, 58 adults (18-25 years) underwent direct anthropometry, standardised 2D photography with calibration, and 3DGS facial reconstruction using a smartphone-based workflow. A predefined set of linear and angular facial measurements was recorded; each measurement was repeated three times by the same observer. Between-method comparisons were performed using paired tests as appropriate. Pearson correlation coefficients were reported to describe association, whereas agreement and potential interchangeability were evaluated primarily using Bland-Altman bias and 95% limits of agreement (LoA); plots were additionally inspected for proportional bias and influential outliers.

3DGS demonstrated small mean differences relative to direct anthropometry for several measurements, with generally narrower LoA than 2D photogrammetry. Correlations were typically higher for 3DGS than for 2D photogrammetry; however, Bland-Altman analyses indicated that agreement varied by variable. For selected measurements, LoA were wide (reaching approximately 10-18 mm for some linear outcomes and exceeding 20° for certain angular outcomes), indicating limited interchangeability for individual-level clinical decisions. Perioral measures showed greater dispersion for 2D photogrammetry, particularly for N-Stm, and a small number of observations fell outside the 95% LoA in ANT vs. 2D comparisons, consistent with occasional landmark identification or reconstruction-related variability.

3D Gaussian Splatting (3DGS) may offer a useful alternative workflow for selected facial analysis applications by enabling the generation of measurable three-dimensional facial models, from which anthropometric variables can subsequently be derived. Although 2D photogrammetry is readily accessible and practical to implement, its inherent limitation in representing three-dimensional anatomy may compromise measurement accuracy in certain clinical contexts. Overall, these findings indicate that 3DGS could support orthodontic practice and research as a 3D model-generation technique; however, further validation across diverse patient groups, acquisition conditions, expanded landmark-based geometric error metrics, and additional outcome measures is warranted before routine clinical adoption can be recommended.