# A Survey of Low-Cost 3D Laser Scanning Technology
## 1 Introduction  
Three-dimensional (3D) laser scanning technology, an advanced surveying and mapping method, has obvious advantages compared to traditional techniques. It combines high efficiency with data quality and accuracy. As the core sensor of 3D laser scanning technology, 3D LiDAR is widely used in many applications, such as terrain survey [1], architectural surveying and mapping [2], automatic driving [3], forest monitoring [4], and plant analysis [5]. However, for the moment, 3D LiDAR is generally expensive and is not consumer-grade yet. In comparison, 2D LiDAR is much more economical, and some 2D LiDARs are already consumer-grade [6]. As two major categories of commercial LiDAR, the differences between 2D LiDAR and 3D LiDAR are as follows: a 2D LiDAR is more economical than a 3D LiDAR, but it obtains less information, and it can only build 2D maps of the environment. On the other hand, a 3D LiDAR can build 3D maps of the environment; however, it is far more expensive than 2D LiDAR. Figure 1 shows a comparison of the maps built by a 2D LiDAR and a 3D LiDAR, respectively. We investigated some commonly used commercial 2D LiDARs and 3D LiDARs; their manufacturers, models, performances, prices, and application fields are listed in Table A1 of Appendix A to provide readers with a more detailed understanding of them. By moving a commercial 2D LiDAR, 3D maps of the environment can be built based on the data of the 2D LiDAR and its movement [8, 9, 10, 11]. Compared with a commercial 3D LiDAR, a moving 2D LiDAR is more economical, while its measurement performance is far inferior to that of the former. For applications that do not require excess measurement performance and require strict cost control (such as the 3D perception of the environment by a commercial home service robot), a moving 2D LiDAR may be useful. From this perspective, a moving 2D LiDAR is necessary and research-worthy. It must be emphasized that a moving 2D LiDAR cannot completely replace a 3D LiDAR. In some applications, with high requirements on real-time performance and measurement ranges, such as automatic driving, a 3D LiDAR with better real-time performance and a longer measurement range is required, while a moving 2D LiDAR is not adequate. However, in other applications, such as the 3D mapping and navigation of an indoor robot, a moving 2D LiDAR can do the job. In these applications, a moving 2D LiDAR can partially replace a 3D LiDAR and provide a new choice for developers and engineers, which can reduce the costs, while the basic functions of 3D mapping are ensured. In addition, a moving 2D LiDAR has the advantages of a flexible field of view and angular resolution. The field of view and angular resolution of a moving 2D LiDAR depend on the movement of the 2D LiDAR. Customizing scan parameters by moving LiDAR is not unique to 2D LiDAR. In [11; 12; 13; 14; 15; 16; 17; 18; 19], since the field of view and angular resolution of some 3D LiDARs are not suitable, researchers obtained the field of view and angular resolutions they wanted by moving these LiDARs. Although low-cost 3D laser scanning technology based on a moving 2D LiDAR is needed in some applications, as far as we know, survey in this research field is relatively unexplored. In view of this, in this paper, we present our survey of low-cost 3D laser scanning technology. At present, there are problems in the application of a moving 2D LiDAR. First, there is the problem of accuracy, primarily due to the error of the 2D LiDAR movement estimation. Specifically, this error may originate from the installation error between the 2D LiDAR and the moving unit [10; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35], or it may originate from the inaccurate movement estimation of the moving unit [36; 37; 38; 39; 40; 41]. Second, the real-time performance of a moving 2D LiDAR is poor (generally, its 3D scanning frequency is lower than 1 Hz), which makes it difficult to be utilized in applications that require real-time performance.