# A Framework of Wearable Sensor-System Development for Urban 3D Modeling
## 2 Design and Production of Wearable Sensor System
### Design of Wearable Sensor System  
Sensor placement criteria were prepared for efficient data acquisition and accurate data fusion, and the design of the wearable sensor system was agreed. The wearable sensor system design criteria determined in this study were as follows:  
1. Criterion 1. One LiDAR sensor is installed to acquire data about the surrounding environment without gaps, while one LiDAR is installed horizontally on the ground \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Sensor**} & \multicolumn{1}{c}{**Model**} & \multicolumn{1}{c}{**Specifications**} \\ \hline \multirow{3}{*}{Camera} & Lens & Sennex DSL315 & Projection model & \begin{tabular}{c} Fish-eye lens \\ (equisolid angle projection) \\ \end{tabular} \\ \cline{2-4}  & Body & \begin{tabular}{c} Cameleon3 5.0 MP \\ Color USB3 Vision \\ \end{tabular} & \
\begin{tabular}{c} Image size \\ (pixel size) \\ \end{tabular} &
\begin{tabular}{c} 2448 \(\times\) 2448 \\ (0.00345 mm) \\ \end{tabular} \\ \hline \multirow{3}{*}{LiDAR} & \multirow{3}{*}{Velodyne HDL-16E} & \multirow{3}{*}{FOV} & Channel number & 16 \\ \cline{3-4}  & & & Horizontal & 360\({}^{\circ}\) \\ \cline{3-4}  & & & Vertical & 30\({}^{\circ}\) (\(\pm\)15\({}^{\circ}\)) \\ \cline{3-4}  & & & Horizontal & 0.5\({}^{\circ}\) (10 Hz) \\ \cline{3-4}  & & & Vertical & 2\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of used sensors. to enable data fusion using algorithms such as SLAM (Simultaneous Localization And Mapping) or ICP (Iterative Close Point). 2. Criterion 2. For efficient data acquisition, the overlapping of FOV is minimized between cameras of the same type, thereby allowing data for a wider area to be acquired with one shot. 3. Criterion 3. The FOV of the optical camera and LiDAR allows sufficient overlap to enable efficient data fusion between different types of sensors. 4. Criterion 4. All sensors are positioned to exhibit a sufficient overlapping of FOV with at least one other sensor to ensure system calibration accuracy. In this study, a wearable sensor system was designed based on the above criteria, followed by a review of the design created through simulation. Figure 1 shows the final determined sensor arrangement and the data acquisition simulation results obtained. As shown in Figure 1, the sensor system comprised two fisheye lens cameras and two LiDARs. According to Criterion 1, LiDAR1 was installed horizontally and LiDAR2 was installed diagonally on the back of the backpack. The diagonal placement of LiDAR2 was determined through a previous study [14] on Li-DAR placement method for efficient data acquisition. According to Criterion 2, the fisheye cameras were installed to face the left and right of the backpack, respectively. Figure 1,c shows the data acquisition simulation results. Here, the red and green crosses in the figure indicate the areas covered by fisheye cameras 1 and 2, respectively, and the cyan and purple dots indicate the areas covered by LiDARs 1 and 2, respectively. The figure shows that the design of the wearable system satisfies each criterion as follows. First, the fisheye cameras were placed such that their FOVs did not overlap to acquire image data for all areas around the system. Next, the LiDAR sensors seamlessly acquired 3D information of the surrounding area, while point cloud data (light blue dots) that can be used in algorithms such as SLAM was acquired through LiDAR1. Finally, with respect to Criteria 3 and 4, the FOV of camera 1 overlapped with that of LiDARs 1 and 2 in the left direction of the system movement direction (yellow arrow), while the FOV of camera 2 overlapped with that of LiDARs 1 and 2 in the right direction. Figure 2 shows the backpack-based wearable sensor system that was produced based on the design. First, a reference LiDAR (LiDAR1 in Figure 1) was installed at the top of the platform, and depth data was obtained horizontally.