# Overlaps between scans and the height of the scanned objects During the flight, TOPODRONE LiDAR scans an area of the surface of a certain width, which is called a "scan". The width of the scan is determined by the technical characteristics of the sensor, the operating altitude of the flight, as well as the difference in terrain. For correct postprocessing of the data obtained from TOPODRONE LiDAR, it is necessary that neighboring scans have a common overlap. It is recommended to provide at least 30% lateral overlap to adjacent scans. Insufficient overlap between scans, especially in combination with significant relief differences, can lead to the formation of an area without data, which significantly reduces the quality of output materials. On the other hand, a higher overlap value allows the most accurate calculation of the calibration angles of Roll, Pitch and Heading. When choosing a specific overlap value, it is necessary to take into account such parameters as the maximum length of the laser beam, the scanning angle (106 degrees for ALS) and the height of the scanned object. To achieve optimal results when performing ALS using TOPODRONE LiDAR, it is recommended to set the following parameters when building a mission:
1 2 3 4 5
LiDAR model, maximum beam length Working height, m Scan width, m Distance between scan centers: % overlap Maximum height of the scanned object: % overlap
30% 40% 50% 60% 30% 40% 50% 60%
TOPODRONE LiDAR 100+ и 100 120 m 50 134 94 81 67 54 15 20 25 30
60 160 112 96 80 64 18 24 30 36
70\* 187 131 113 94 75 21 28 35 42
80\*\* 136 96 82 68 55 24 32 41 49
TOPODRONE LiDAR 200+ 300 m 90 240 168 144 120 96 27 36 45 54
100 267 187 161 134 107 30 40 50 60
110 292 205 176 146 117 33 44 55 66
120\* 240 168 144 120 96 36 48 60 72
130\* 260 182 156 130 104 39 52 65 78
140\*\* 235 165 141 118 94 42 56 70 84
150\*\* 250 177 152 126 101 45 60 75 90
Table 1. Dependence of the distance between the scan centers on the overlap and the working height. \* The specifications are given for a scanning angle of 90 degrees. \*\* The specifications are given for a scanning angle of 80 degrees. With such characteristics, there is a significant decrease in the density of points. [![Перекрытие LiDAR.jpg](https://knowledge.topodrone.com/uploads/images/gallery/2024-10/scaled-1680-/perekrytie-lidar.jpg)](https://knowledge.topodrone.com/uploads/images/gallery/2024-10/perekrytie-lidar.jpg) The density of the resulting point cloud depends on factors such as flight speed, altitude, and surface reflectivity. As nominal initial values, it is recommended to conduct flights at a drone flight speed of 6 m/s at an operating altitude of 60 m for TOPODRONE LiDAR 100, 100+ and 100 m for TOPODRONE LiDAR 200+ with 40% overlap. Further changes to these parameters must be made taking into account the features of the terrain, weather conditions and the maximum height of the scanned objects.