# Towards a Multi-Perspective Time of Flight Laser Ranging Device Based on Mirrors and Prisms
## 4 Discussion  
This section discusses the meaning of measured data. Firstly, the direct measurement method is discussed where the importance of walk error compensation is illustrated. Following that, redirecting FOV with mirrors and reasons for the trend of measurement becoming increasingly negative for only some distances between the ranging device and dusted mirror is explained. Our results are also compared to similar data from preexisting studies. Lastly, we take a look at what measurement results for redirecting light with a prism suggest. Figure 10: (**a**) Measurement error for the entire suite of measurements, from 5 cm to 55 cm distance between the ranging device and prism. (**b**) Compensated measurement data for the same datasets where x-axis is the measurement number. Which line corresponds to which configuration can be read from the legend. The explanation for the presented data is in the discussion section, where Figure 10 is referenced. Figure 9: Shape of return signal for the configuration with a dusted protected silver first surface mirror. Return signal with no target in the detection range of the ranging device is shown in blue. Return signal with a poorly reflective target in sight is shown in orange. The root cause of the presence of the unwanted signal, and the consequent waveform’s changes are presented in the discussion section, where Figure 9 is referenced. The importance of walk error compensation is observed in Figure 7a. It shows uncompensated and compensated measurements with orange and blue lines, respectively. It can be observed that the uncompensated measurements show a target at significantly greater distance than expected. Beyond the partially dead zone, the error increases with distance, as best illustrated in Figure 7b. It shows the uncompensated measurement error versus the set distance. Figure 7c shows the reflected pulse's width, which decreases with distance beyond the partially dead zone, extending to approximately 17 cm beyond the sensor. In this zone, not all transmitted light is in the receiver's FOV, as illustrated in Figure 1. Figure 7d provides a reference for further ranging methods, as it shows the measurement error and the standard deviation of measurements for the direct ranging. A trend observed here and in all remaining measurements is that standard deviation increases slightly with distance but does not vary greatly between different configurations, as it can be observed in Table 1. It provides an overview of the maximal measurement standard deviations. The values are gathered only from data points where the total distance between the ranging device and target is greater than 13 cm, as to eliminate the data points just beyond the ranging device's dead zone, which shows a large deviation from the expected values even in a direct measurement configuration. A more or less direct comparison between direct measurements and the ones reflected by a mirror at 5 cm can be made. This is because the minimal distance between the ranging device and target in both cases was 10 cm in both cases. By comparing Figure 8a to Figure 8c (FOV) redirected by a clean first surface and a regular mirror), any differences are within the margin of measurement error and show outstanding similarity in shape. When Figure 7d (direct measurement) is taken into consideration as well, some minor differences can be observed among the three datasets, but those are once again below the designed accuracy threshold. The rest of the measurements with FOV redirected by a clean mirror were still very similar to the ones obtained directly in the overlapping measurement range. Worse results were expected for the configurations with dusted mirrors. When comparing measurement results for clean mirrors to their dusted counterparts in Figure 8b and Figure 8d for the dusted first surface and regular mirror, respectively, essentially no differences can be observed up to the 300 mm mark.