## 4 Discussion  
As already stated, nearly 1900 images were taken of the campus area. In this section, a number of views of the campus area have been chosen for comparison to illustrate similarities and differences between the environment in the real world and the corresponding environment in Unity software, see Figures 10-13. Figures 10a and 11a depict the campus area of the LUT University in the real world, and Figures 10b and 11b illustrate the area as it is created using photogrammetry. As the figures show, the created environment reflects the real world environment appropriately. Cloudy weather facilitated proper matching of the points collected by the laser scanner with the corresponding points in the images. As Figures 10b and 11b demonstrate, the physical dimensions of the buildings, their locations,  
Figure 10: Comparison between the LUT University campus area in the real world and in Unity software using photogrammetry: (**a**) Real world and (**b**) Unity environment. as well as the distances between the structures have been correctly generated. The paths and streets are created without notable failures. Figures 12a,b and 13a,b show the main entrance of the University in the real world and in the graphical software, respectively. Comparing the point of views, the distances between points are measured in both the real world and the graphical software. Table 1 shows the values for the point distances. As the table shows, the 3D graphical environment constructed by photogrammetry procedure reflects the real world environment appropriately. Figures 12a and 13a show the main entrance area of the LUT University main building. Figures 12b and 13b are the corresponding scenes generated using the photogrammetry approach. As the figures show, the postprocessing phase in the photogrammetry is accomplished with acceptable accuracy. Nearly all points (generated by the laser scanner) match properly with the corresponding points in the images taken by the drone. The buildings are created appropriately and there is no major distortion in the structures. Comparisons of the dimensions, colors, and textures in Figure 12a,b show that Figures 12b and 13a provide a highly accurate reflection of the real world. As pointed out, to construct the 3D environment model out of the planar images, photogrammetry has been used. Figure 11: A comparison between the LUT campus buildings in real world and in the graphical software using the photogrammetry approach: (**a**) Real world and (**b**) Unity environment. In this study, a laser scanner has been utilised to increase the visibility and accuracy of the building surfaces, such as walls and windows. In addition, the environment will be used in the application of physics based real-time simulation models. Therefore, both methods have been utilised to keep the environment as realistic as possible. Figure 12: LUT University main entrance in the real world and in the graphical software using the photogrammetry-based approach: (**a**) Real world and (**b**) Unity environment. As mentioned earlier, the graphical software can be connected to the simulation software to run simulation models. The environment of the LUT University campus area can be used for real-time simulation models. Figure 14 shows a real-time simulation model of an excavator which has been imported to the university campus environment. \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Name** & **D1 (m)** & **D2 (m)** & **D3 (m)** & **D4 (m)** \\ \hline Real world environment & 5.6 & 4.3 & 6.45 & 19.6 \\ Graphical software environment & 5.6 & 4.3 & 6.45 & 19.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The distance values shown in Figures 12a,b and 13a,b. Figure 13: Comparison between the textures in the real world and created in the graphical software using the photogrammetry-based approach: (**a**) Real world and (**b**) Unity environment. The model is of a real excavator with 22 tons of operating weight. The excavator-simulated model consists of nine bodies.