## 4 Lab Experiment
### Results
#### 4.2.4 Maximum Number of Simultaneous Recognition and Tracking  
Table 2 shows the results of the maximum number of simultaneous recognition and tracking experiment. Vuforia's overall performance is better than the others, while ARCore shows the worst performance. Vuforia and MAXST simultaneously recognize multiple products and display the AR content. In contrast, ARCore does not support simultaneous recognition, so it recognizes at most one target and shows the relevant AR content. Although Vuforia and MAXST support simultaneous recognition, both of them do not simultaneously display AR content for the same targets. Even if two of the same product are seen by the camera, AR content relevant to them is shown over only one of them. In the case of Vuforia, when five distinct products out of ten are seen by the camera, all of them are recognized. However, MAXST has the limitation that at most three targets are simultaneously recognized.  
The number of products simultaneously seen by the camera and the number of products simultaneously recognized are different depending on the product arrangement and smartphone orientation. In the case of horizontal arrangement and horizontal orientation, MAXST recognizes three products, which is the maximum number of simultaneous recognition in many trials. However, it recognizes only one target three times out of 9 trials. When the phone's orientation is vertical, MAXST tends to recognize products in the middle, and only one or two are recognized. Vuforia well recognizes all of the distinct products seen by the camera at the same time. ARCore does not always successfully recognize a product, even though several distinct products are seen. It recognizes one target product  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Product** & **Phone** & **\# of Products** & **\# of Distinct** & & & \\
**Arrangement** & **Orientation** & **Seen by Camera** & **Products Seen** & & & \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} Horizontal \\ (2 rows) \\ \end{tabular} } & Horizontal & 10 & 5 & 2.3 & 5 & 0.33 \\ \cline{2-6}  & Vertical & 6 & 3 & 1 & 3 & 0.56 \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Vertical \\ (3 rows and one on the top) \\ \end{tabular} } & Horizontal & 9 & 5 & 3 & 5 & 0.22 \\ \cline{2-6}  & Vertical & 10 & 5 & 1.2 & 5 & 0.33 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Average number of products simultaneously recognized and tracked (distance: 70 cm).  
Figure 7: Maximum recognizable occlusion (numbers inside parentheses are standard deviations).  
only 2-5 times out of 9 trials. When the distance between the smartphone and the products is reduced to 50 cm, it is able to recognize a product better.  
We examine potential issues that may occur when multiple products are simultaneously recognized and their relevant AR content is shown at the same time. Usually, the products on a shelf in a store are densely placed without much space between adjacent products. In such a condition, AR contents for different products are likely to overlap with each other, and thus some of them are not visible, as shown in Figure 8. When the content is placed on the left or upper side of a product, adjacent products can be covered by the content. Thus, it may be difficult for users to check the products directly on the smartphone screen; users may have to move the smartphone to see the products. These issues can degrade the user experience of AR applications.