Beatriz Mañas Ballester, Sara Gil Mora, Alfredo Ballester Fernández, Sandra Alemany Mut, Eduardo Parrilla Bernabé, Ana Piérola Orcero, Mateo D. Izquierdo Riera, Jordi Uriel Moltó, Beatriz Nácher Fernández, Vicent Ortiz i Castelló, Álvaro F. Page del Pozo, Juan Carlos González García

Instituto de Biomecánica (IBV) Universitat Politècnica de València. Edificio 9C. Camino de Vera s/n (46022) Valencia. Spain

The Instituto de Biomecánica (IBV) has carried out a study that quantifies the precision and validity of 3D foot scanning technology using a smartphone, as developed by the IBV, compared with traditional methodologies such as manual measurements and other commercial solutions currently on the market. The results confirm that the IBV technology is as precise as the reference solution, much more reliable than manual measurements performed by an expert, and offers great opportunities for application in economic sectors where the possibility of scanning anywhere and at low cost are important for deployment and scalability.

INTRODUCTION

The growth of online commerce in the footwear industry is unstoppable. However, there are significant barriers that are slowing down this growth and limiting its profitability, the most important of which is the considerable number of returns due to uncertainty when selecting the shoe size. 3D measurement of customers’ the feet is the way to solve this problem and even to boost new business models such as mass footwear customization.

Foot dimensions can be obtained in all manner of ways today, ranging from manual measurements (customers can be measured at home or by an expert in the shop) to high-res 3D scanners. The Instituto de Biomecánica (IBV) has recently developed a new technology based on artificial intelligence that allows you to scan a foot in 3D with a smartphone, revolutionizing the market by making it possible to measure consumers’ feet no matter where they are and at very low cost.

Different factors can affect the choice of the best technology for a specific application, such as cost, user experience, robustness or maintenance requirements, etc. The precision of the measurement system is one of the most critical factors. If we do not have valid and reliable information of the foot and the footwear, it is impossible to provide a good recommendation as far as the size is concerned.

One of the challenges when it comes to choosing which of the existing 3D foot scanning technology to use is that no information exists as to the precision of the devices in real usage conditions, nor in scientific studies or in the technical specifications that the companies provide. In addition, there is the fact that the 3D scanning of people in real conditions is complex. If we scan a person's foot several times, factors such as posture or muscle contraction always vary slightly between each repetition, giving rise to different measurements for the same foot (Figure 1).

Figure 1. Variation in the 3D shape of the same foot within different scans repeated under the same conditions.

In this way, the objective of the study presented here is to determine the precision and validity of different measurement techniques, among which is the scanning technology using a smartphone developed by the IBV.

DEVELOPMENT

We have analysed three methods of measuring the foot in real conditions:

♦ Traditional manual measurements taken by a trained expert

♦ 3D scanning technology, taking as a reference Infoot, the high-res laser scanner from I-ware company.

♦ The new IBV scanning technology: the Feet/IBV mobile app and an In-store scanner, DOMEscan/IBV (Figure 2).

Figure 2. New data-driven exploration technology developed by IBV.  Left: Avatar3D.Feet/IBV smartphone app; Right: In-store foot scanner DOMEscan/IBV.

We carried out 3 repeated, non-consecutive measurements of the feet of 16 subjects (8 women and 8 men) with each method. The precision of each method was evaluated using Standard Error of Measurement (SEM) which provides the magnitude of the random error in the same measurement units (Table 1). Validity was assessed by comparing the results of the different methods (Figure 4).

Table 1. Precision of measurements (SEM) in millimetres (mm)

RESULTS

Precision as can be seen in Table 1 and in Figure 3, digital techniques are able to achieve pinpoint precision for most measurements, except on the perimeter of the toes, possibly because it is the most articulated part of the foot and because this is where there is greater variability, due to tiny changes in posture and load (Figure 1). The technology developed by the IBV is as precise as the high-res 3D scanner (Infoot), both of which surpass the manual measurements made by the experts.

Figure 3. Average accuracy of the 3D surface of the feet measured by different digital scanning technologies.

Validity

Compatibility between methods (DOMEscan/IBV, Avatar3D.Feet/IBV and traditional anthropometry versus Infoot’s 3D scanner, taken as a reference method of measurement) are presented in figure 4. DOMEscan/IBV and Avatar3D.Feet/IBV measurements can be considered compatible with the measurements of the Infoot reference scanner, given that the differences are small (1mm or less) and not significant.

Figure 4. Differences (bias) between foot scanning methods in mm (Mean and standard deviation).

However, significant differences do appear between the three digital measuring techniques and the traditional methods. These systematic differences may be due, among other factors, to the pressure exerted on the soft tissue during manual measurement and the difficulty in applying the tape measure in some measurements.

CONCLUSIONS

The precision of the digital techniques seems adequate both for the recommendation of the size and for the design of custom-made footwear. The scanning technology developed by the IBV (DOMEscan/IBV, Avatar3D.Feet/IBV) is as precise as high-res 3D scanners and more reliable than manual measurements made by experts. The main advantage of the IBV technology in comparison to current 3D scanners is its simplicity and efficiency, which translates into lower costs and faster processing because it does not require cameras, projectors or high-end computing resources.

This technology, in addition, can be integrated into any smartphone using the Avatar3D.Feet/IBVapp, which means it can be used anywhere, with great potential for scalability. In the case of outlets with high footfall such as shoestores, the technology can be integrated into a low-cost and easily portable scanner (DOMEscan/IBV) that allows serial measurement with an excellent user experience.