# Development and Performance Assessment of a Low-Cost UAV Laser Scanner System (LasUAV)
## Materials and Methods
### In-Flight Setup: Laser, INS, and GNSS RTK Measurement Uncertainty Analysis  
In S3, the in-flight setup, the uncertainty of the LasUAV was assessed through an analysis using datasets from the test field composed of the control surface of a box. The components of the LasUAV system under investigation with this setup were the laser scanner, the INS, and the GNSS RTK receiver. This setup allowed the assessment of three sources of uncertainty: (i) uncertainty in Z associated with a single passage over the target; (ii) uncertainty in Z associated with multiple passages (from one to nine) over the target; and (iii) uncertainty in the horizontal positioning of X and Y of the target associated with multiple passages (from one to nine).  
A flat area of 10,000 m\({}^{2}\) with a box as a target was sampled with an automatic flight at an average flying height of 10 m (HFOV = 11.55 m) and horizontal velocity of 2 m/s\({}^{-1}\) (Figure 8).  
Figure 8: The test area with the target (biggest box) used to assess the accuracy of LasUAV in in-flight conditions.  
Figure 7: The two subsets used to calculate uncertainty and accuracy associated with height measurements: an angular static dataset (blue) and an angular dynamic dataset (red).  
The LasUAV traveled through the area, scanning the target in nine repeated passages. For each passage over the target, an analytical procedure was developed to extract subsets of the entire point cloud corresponding to individual passages and to spatially locate the target. The position of the target at each flight passage, represented by a rectangle coincident with the top of the box, was determined within each point cloud with an optimization procedure; the actual position was computed among all the possible positions as the one that minimized the sum of residuals (a residual being the difference between the elevation value of each point falling inside the rectangle and the true elevation of the top of the box). For the cloud points falling inside the rectangle representing the top of the box, the mean and the standard deviation of \(Z\) were computed.  
An analysis of possible combinations of one passage (i.e., nine combinations of one passage from the set of nine passages), two passages (36 combinations of two passages from the set of nine passages), three passages (84 combinations of three passages from the set of nine passages), four passages (126 combinations of four passages from the set of nine passages), five passages (126 combinations of five passages from the set of nine passages), six passages (84 combinations of six passages from the set of nine passages), seven passages (36 combinations of seven passages from the set of nine passages), eight passages (nine combinations of eight passages from the set of nine passages), and nine passages (one combination of nine passages from the set of nine passages) was conducted to assess the variation in uncertainty in \(Z\) in the case of UAV flights made with multiple passages, i.e., to assess the overall variability of the target position among multiple passages, related to the positioning accuracy of the system. Uncertainty was calculated as the average value of the standard deviation of all possible combinations for each set of passages. For example, in the combination of two passages over the nine passages in the set, uncertainty was calculated as the mean of 36 values of standard deviation; in the combination of three passages over the sample of nine passages in the set, uncertainty was calculated as the mean of 84 values of standard deviation, and so on. This analysis allows us to understand how many passages over the area of interest made in a UAV campaign can affect the overall uncertainty of the point cloud.