# Advanced Methods for Point Cloud Processing and Simplification
## 8 Results
### Optical Rangefinder for Space Scanning  
As the remote sensing device for space scanning, we used our developed optical rangefinder. The described 3D range scanning system is part of a bigger project called ARES (Autonomous Research Exploration System), which is described in references [33; 34]. The rangefinder sweeps a laser point into the vertical line and in each point of this line, it is possible to estimate the point position in the space. The measurement principle is based on the triangle similarity described in reference [35]. For detailed information on how to determine a 3D point in a scanned space, see references [35; 36]. The whole measuring device consists of a tripod; a high-quality Basler color camera with a resolution of \(2590\times 1942\) pixels; a green 200 mW laser diode; an optical filter with an angle of 90 degrees for vertical swapping of the laser beam; and a fast and powerful stepping motor for 360 degrees rotation. The following figure shows the practical measurement Figure 16a with measurement frame Figure 16b.  
Figure 16: Measurement illustration: (**a**) Developed 3D scanner; (**b**) Measurement frame.  
Figure 15: Detected vertices: (**a**) Vertices of Figure 14a; (**b**) Vertices of Figure 13d.  
We replaced the used camera lens with a lower focal length to cover a higher range in the height during the development of this device. The lower focal length caused the undesired barrel distortion effect. This effect elimination is described in reference [37]. In one of our recent papers ([38]), we developed the automatic algorithm for the best undistortion parameter estimation. The laser line is segmented from a static measurement frame by the HSV GMM (Gaussian Mixture Model). The HSV color model best covers the intensity range of the used laser (see references [39; 40]). The intensity of laser pixels in the measurement image depends on the distance from a scanning object and its reflection of the laser spectrum. Nevertheless, in the measured frames, pixels with a low and high intensity similar to the spectrum of a laser or reflected laser light can occur. For the robustness of the position determination and distinguishing from a laser colored object, it is important to analyze, the laser pixel intensity as well as the laser element shape. A statistical analysis of both parameters offers to detect the main laser line intensity correctly. More details about the best laser element selection and the main laser intensity estimation is described in references [41; 42]. We also implemented the fusion of image data from the camera with points in space to achieve a colored point cloud by using a template matching method in two measurement frames (see reference [36]). The measurement system can determine the vertical laser line with a half-pixel accuracy. The accuracy of the distance determination for the actual rangefinder configuration is shown in Figure 17.  
The maximal error is 3.5% in the range of 15 m. In the bigger distances, the laser line is closer to a measurement frame center, and the change of position of about one pixel causes a bigger change in the measurement distance. This dependency is non-linear and causes bigger measurement errors. More about this non-linearity and calibration of the optical rangefinder is described in reference [43]. In comparison with the present expensive professional laser scanners, our rangefinder can be labeled as a home 3D scanner.