# A Review of Commercially Available 3D Surface Imaging Systems for Body Composition Estimation
## 4 Discussion
### System Details  
Although all commercially available 3D surface imaging systems reviewed in this paper were based upon structured light they demonstrated a variety of system details. The systems demonstrated capture durations of 7 to 90 s. Whilst this is quicker than manual measurement, it is still possible for movement artefacts to influence the accuracy of the data collected. In addition, the systems were reported to cost between $799 to $10,000, thereby evidence systems are available at a variety of costs, and thus accessible for thosewith a variety of budgets. Although reported within Daanen & Haar's review of 3D surface imaging systems [21], no system manufacturer reported capture volume. It is possible that this information is reflected in the distribution of the maximum user height and weight. However, as users could present the same height and weight but different body girths, such information would have been valuable to confirm the suitability of the systems for different body sizes.  
Accuracy of the Humanoid Mesh, the Anthropometrics Extracted, and the Predictive Algorithms  
Due to instrument imprecision and human inconsistencies, error is inevitable, and complete 100% accuracy is unachievable [38], thus all systems will present degrees of error. However, of the commercially available 3D surface imaging systems reviewed, only four of the six manufacturers reported accuracy for one field; humanoid mesh, anthropometrics, or body composition estimates, of which none reported accuracy for all fields. For those that did report accuracy for body composition estimates, it ranged between 2.5--5%. This is comparable to the reported accuracy values within published literature. For example, [PERSON] et al. [19] reported RMS-%CV of 2.3-4.3% for body fat percentage, 2.5-4.3% for fat mass, and 0.7-1.4% for fat-free mass in an assessment of 4 systems, when compared with 4C model of air displacement plethysmography, DEXA, total body water and bioimpedance spectroscopy of 139 participants. [PERSON] et al. [8] reported the predictive body composition algorithm of a Fit3D Proscanner to demonstrate a root mean square error of 2.4 kg for fat mass and 2.2 kg for fat-free mass, when compared to DEXA, when measuring 39 participants.  
Transparency regarding how accuracy is established is essential to ensure informed judgment of the systems outputs and their suitability for use within different contexts [39]. However, only two system manufacturers provided details regarding the process through which accuracy was established. Typically, this was because the accuracy had been established in an external research project. However, it is worthwhile to note that reported accuracy is only valid for the hardware and software versions, population samples, and predictive algorithms used at the time of data collection. Thus, any alterations to these would render reported accuracy invalid. It is unknown why 3D surface imaging system manufacturers are not reporting their systems' accuracy for one or all fields. With the countless potential applications of 3D surface imaging devices, there are potential applications for systems with different degrees of accuracy. By not reporting 3D surface imaging systems accuracy, we risk the incorrect use and misinterpretation of outputs, thereby damaging the reputation and potential usefulness of this technology.  
Although not sought within this review, it was noted by the researchers that no 3D surface imaging system manufacturer publicly reported the fidelity of the 3D humanoid mesh created through their system; the degree to which the humanoid is comprised of true data and systematic data, the type and amount of smoothing, filtering and repair the humanoid undergoes during post processing. Such information is important for the appropriate selection, use, and interpretation of outputs. This is likely to become increasingly important as the prevalence of app-based technologies, specifically those using passive stereo of front and side profile images in which such techniques are more prevalent, increases.