Smartphone Photogrammetric Assessment for Head Measurements

Abstract

The assessment of cranial deformation is relevant in the field of medicine dealing with infants, especially in paediatric neurosurgery and paediatrics. To address this demand, the smartphone-based solution PhotoMeDAS has been developed, harnessing mobile devices to create three-dimensional (3D) models of infants’ heads and, from them, automatic cranial deformation reports. Therefore, it is crucial to examine the accuracy achievable with different mobile devices under similar conditions so prospective users can consider this aspect when using the smartphone-based solution. This study compares the linear accuracy obtained from three smartphone models (Samsung Galaxy S22 Ultra, S22, and S22+). Twelve measurements are taken with each mobile device using a coded cap on a head mannequin. For processing, three different bundle adjustment implementations are tested with and without self-calibration. After photogrammetric processing, the 3D coordinates are obtained. A comparison is made among spatially distributed distances across the head with PhotoMeDAS vs. ground truth established with a Creaform ACADEMIA 50 while-light 3D scanner. With a homogeneous scale factor for all the smartphones, the results showed that the average accuracy for the S22 smartphone is −1.15 ± 0.53 mm, for the S22+, 0.95 ± 0.40 mm, and for the S22 Ultra, −1.8 ± 0.45 mm. Worth noticing is that a substantial improvement is achieved regardless of whether the scale factor is introduced per device.

Craniofacial 3D Morphometric Analysis with Smartphone-Based Photogrammetry

“…The accuracy results in measuring landmarks ( Table 7 ) are in line with other smartphone-based photogrammetric studies independently of the model and branch of smartphones used [ 36 , 37 , 38 ]. In [ 36 ], the authors point out the significant differences between the individual camera models in terms of interior orientation stability and propose using geometric pre-calibration beforehand instead of self-calibration.…”

“…In [ 36 ], the authors point out the significant differences between the individual camera models in terms of interior orientation stability and propose using geometric pre-calibration beforehand instead of self-calibration. However, the authors in [ 37 ] emphasise the need for proper scaling as being a more relevant factor for improving smartphone-based accuracy rather than performing geometric calibration in a separate process or pre-calibration. In addition, ref.…”