# A Survey of Low-Cost 3D Laser Scanning Technology
## 4 Problems of a Moving 2D LiDAR  
For a moving 2D LiDAR, a series of problems need to be solved to enable it performs better. For the six categories of prototypes mentioned in Section 3.6 of this paper, due to the different designs of the prototypes, the specific problems that need to be solved may be different. We listed the problems of a moving 2D LiDAR in Table 2. Next, we will discuss these problems in detail one by one.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Problems**} & \multirow{2}{*}{
\begin{tabular}{c} **Categories** \\ **of Problems** \\ \end{tabular} } & \multicolumn{6}{c}{**Categories of Prototypes**} \\ \cline{3-8}  & & **1** & **2** & **3** & **4** & **5** & **6** \\ \hline Problem 1.1. The measurement error of the 2D LiDAR. & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 1.2. The error caused by the motor. & & \(\bullet\) & \(\bullet\) & & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 1.3. The error caused by the assembly inaccuracy & & \(\bullet\) & \(\bullet\) & & \(\bullet\) & \(\bullet\) & \\ between the 2D LiDAR and the rotating unit. & & \(\bullet\) & & & \(\bullet\) & \(\bullet\) & \\ Problem 1.4. The error caused by the synchronization inaccuracy between the 2D LiDAR and the rotating unit. & & \(\bullet\) & & & \(\bullet\) & \(\bullet\) & \\ Problem 1.5. The error caused by the assembly inaccuracy & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ between a moving 2D LiDAR and the mobile platform. & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 1.6. The error caused by the estimation inaccuracy of & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ the movement of the mobile platform. & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 2.1. The negative correlation between the real-time performance and the density of the 3D point cloud. & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 2.2. The distortion of the 3D point cloud caused by & & \(\bullet\) & & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 2.3. The distortion of the 3D point cloud caused by & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ the moving objects in the environment. & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 3.1. The density distribution of the 3D point cloud built by a moving 2D LiDAR. & & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 3.2. The fusion of a moving 2D LiDAR and 2D LiDAR SLAM. & & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 3.3. A push-broom 2D LiDAR, which is used for the detection of the obstacles in front of the vehicle. & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ Problem 3.4. The fusion of a moving 2D LiDAR and a camera. & & & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ \hline \hline \end{tabular} Note: the six categories of prototypes in Table 2 are (1) a rotating 2D LiDAR, (2) a pitching 2D LiDAR, (3) a push-broom 2D LiDAR, 4) an irregularly rotating 2D LiDAR, (5) an obliquely rotating 2D LiDAR, and (6) an irregularly moving 2D LiDAR, respectively.  
\end{table}
Table 2: The problems of a moving 2D LiDAR.  
For each problem, the categories of the prototypes corresponding to it have been indicated. These problems focus on different points. Among them, the improvement of the accuracy and real-time performance are two points, which should be urgently solved.