## 1 Introduction  
LiDAR is a technique for measuring the distance of any object or surface point remotely using laser light. As a result of developments in electronics and computer techniques, LiDAR has gained significant progress in three-dimensional (3D) measurement. Moreover, mobile measurements can be made during the motion of the object or measuring instrument. This situation has opened the door to the use of 3D LiDAR tools in a wide variety of applications. Currently, LiDAR is a measurement technique for a wide range of applications, such as mapping [1], unmanned vehicle navigation [2], 3D digitization [3], robotics [4], building information modeling [5], etc. A single-solution LiDAR measurement technique is not proper for all these applications. The developments in LiDAR technology have provided new techniques for measuring 3D point clouds (Figure 1). These innovations are in the form of reducing the size, weight, and cost of LiDAR devices while increasing their measurement speed and density. In this way, LiDAR measurement from aerial and terrestrial mobile platforms has become more widespread. TLS has accelerated 3D measurement with intensive spatial data in a short time. Thanks to the advantages they provide, TLS is widely used for object modeling and topographic surveying [6; 7]. They are ground-dependent instruments for static measurements. The integrated use of laser beams with sensors such as GPS and inertial measurement units (IMU) has enabled mobile 3D measurement [8; 9]. Terrestrial mobile LiDAR with mobile vehicles is used in the creation of 3D models of urban areas and corridor mapping [10]. Aerial LiDAR is used for mapping large areas and creating a digital elevation model. This situation has especially highlighted the LiDAR method in providing data to geographical information systems [11]. On the other hand, thanks to the fact that LiDAR measurements can be made in a short time, changes in the measurement area can be easily reflected in databases. A new era has been started in LiDAR measurement with compact time-of-flight (ToF) cameras used in indoor measurements. These cameras using the ToF technique can simultaneously measure the entire field of view (FoV) and repeat this process many times per second. Thanks to its high measurement speed, mobile measurements can also be made by carrying the camera in hand. In addition, the use of LiDAR in robotic navigation, motion analysis, three-dimensional measurement, and deformation imaging has become widespread with the use of ToF cameras [12]. However, due to the laser-beam structure, ToF cameras are not suitable for outdoor surveys. This situation has led to the search for a new technique for measuring the LiDAR point clouds, and a flash LiDAR measurement technique was developed in the early 2000s. Flash LiDAR cameras with imaging sensors in matrix form are used in navigation, security, mobile mapping, 3D modeling, and object tracking [13; 14; 15]. The use of a flash LiDAR camera is common, especially in the navigation of autonomous vehicles [16]. Thanks to its low weight and integrated use with the other sensors, flash cameras are also used in unmanned aerial vehicle (UAV)-based mobile mapping. The single avalanche photodiode (APD) technique used in LiDAR photon imaging has turned into multiple APD sensors in a pixel array with flash LiDAR [17]. According to the working mode of the APD arrays, flash LiDAR has two types of APD array, namely the linear mode and the Geiger mode [18]. Geiger-mode LiDAR (GMLiDAR) allows LiDAR measurements to measure larger areas in a short time. Single-photon avalanche diode (SPAD), which is a different application of GMLiDAR and has been used for the last few years, enables high-density point measurement at a low energy level [19]. The laser photon imaging technique affects the LiDAR reflection intensity, measuring distance, accuracy, and point density. On the other hand, depending on the measurement technique, the energy requirement also changes.