# A Novel Method Using 3D Interest Points to Place Markers on a Large Object in Augmented Reality
## 3 Experiment and Discussion
### Experimental Environment and Methodology
#### 3.1.2 Methodology  
1. Content for augmentation and measurement  
To validate the proposed method through experiments, content that augmented the virtual object based on multiple markers was developed. The content was developed by using the 3D content development tool 'Unity (2020.3.12f1 version)' and the officially supported HoloLens 2 content development library'mixed reality tool 'kit (2.7.3 version)'. The developed content (a) augmented a virtual sphere at the index fingertip in real time through a pointing gesture with the right hand (HoloLens 2 has the highest hand tracking accuracy when the pointing gesture is maintained in the right hand [37; 38]), and (b) placed a virtual marker at the position of the augmented sphere by controlling a wireless mouse with the left hand, as shown in Figure 13.  
In a simple test using the real right hand and a physical marker, it was confirmed that when the virtual sphere augmented at the index fingertip was positioned at the end of the marker, an error occurred approximately 0.4 to 1.5 cm, as shown in Figure 14. This error is considered as the relative position consistency problem in this paper. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**DM**} & \multicolumn{3}{c}{**Dimensions**} \\  & **Width** & **Height** & **Length** \\ \hline Real (mm) & 1595 & 1485 & 3595 \\ Virtual [35] & 1596.99 & 1511.19 & 3606.88 \\ Error (mm) & 1.99 & 26.19 & 11.88 \\ Tolerance (mm) & \(\pm\)30 & \(\pm\)50 & \(\pm\)40 \\ Error rate (\%) & 0.125 & 1.764 & 0.330 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of \(\text{DM}_{\text{R}}\) and \(\text{DM}_{\text{V}}\). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**DA**} & \multicolumn{3}{c}{**Dimensions**} \\  & **Width** & **Height** & **Length** \\ \hline Real (mm) & 1800 & 1440 & 4570 \\ Virtual [36] (2\(\times\)) & 1803.89 & 1456.39 & 4558.64 \\ Error (mm) & 3.89 & 16.39 & 11.36 \\ Tolerance (mm) & \(\pm\)40 & \(\pm\)60 & \(\pm\)50 \\ Error rate (\%) & 0.216 & 1.138 & 0.249 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of \(\text{DA}_{\text{R}}\) and \(\text{DA}_{\text{V}}\). The virtual marker was then placed on the real object by referring to a marker position image recorded for the virtual object, as shown in Figure 15. When the placement of the markers was completed, the content verified whether all the markers were at the initial input positions. If any markers were different from the initial position, the content allowed to reposition them using the right index finger and mouse. Figure 14: Simple test result using a physical marker (unit: cm). Figure 13: Marker placement process in the developed experimental content: (**a**) real-time tracking of the right index fingertip; (**b**) placing virtual marker when controlling the mouse with the left hand. Figure 15: Marker placement process: (**a**) reference image; (**b**) marker placement. Once it was confirmed that all the markers were placed correctly, the developed content performed registration based on the iterative closest point (ICP) using the relationship between the placed markers and the markers positioned relative to the virtual object, and finally augmented the virtual object. Figure 16 shows the results of the augmented registration on the DM and DA. The developed content added a World Anchor property to the virtual object when the augmentation and registration of the virtual object were completed. This property is a technology that maintains the position and rotation of virtual objects placed in the real world, even if camera pose estimation errors occur and accumulate in markerless environment [39; 40; 41; 42]. HoloLens 2 uses the perceived surrounding space and sensors on the device to anchor a virtual object to the real world. Figure 17 shows the spatial awareness of the real object. Then errors, which are the registration performance of the augmented virtual object, were measured using this content.