## 3 Example Case
### Procedure for Three Dimensional Environment  
Figure 8 shows the process steps for a photogrammetry approach using a drone and a laser scanner to generate a three-dimensional environment for the use of real-time simulation. As Figure 8 illustrates, the photogrammetry starts with the drone taking thousands of images. The drone flies at a specific height and takes images with a specified overlap between each two continuous images. Simultaneously, a laser scanner scans the environment and generates a point cloud of structures, the ground, trees and other objects. The images and point cloud are exported to a postprocessing software to generate an initial three-dimensional environment. ReCap software was utilized as the postprocessing software in this study. The generated initial environment is exported to a graphical software to create a detailed environment that can be employed in a real-time multibody simulation. In the procedures used, the drone captures the images and the laser scanner collects the  
Figure 8: Process steps to generate an environment for real-time simulation software using a photogrammetry approach and Unity software. Figure 7: FARO S70 laser scanner. point clouds. The laser scanner software has an altimeter, an inclinometer, a compass, and a color recognition feature. Prior to starting photogrammetry and the laser scanning processes, a ground reference point for the laser scanner and the drone are defined. Based on the ground reference point, the postprocessing software identifies the corresponding points on surfaces in both methods. Prior to the operation, the laser scanner locations were predefined during its operation. This pre-definition helps with point matching and line matching between images and point cloud data. The point cloud data collected by the laser scanner are exported to the photogrammetry software, ReCap, where the alignment between points is accomplished. Afterwards, the images are exported to the software, where the alignment between images will be done. At the final stage, the alignment between the point cloud data and images is accomplished based on the check points. As mentioned previously, the laser scanning process is performed to demonstrate the precise textures of the walls. At this stage, the multibody simulation software models can interact with the generated environment in the graphical software platform. Accordingly, there is no need to export the generated environment from the graphical software to the real-time simulation software. Instead, a model and its environment can be illustrated in the graphical software platform and controlled by the simulation software. Figure 9 shows an example of a model and an environment in the graphical software that can be controlled by the real-time simulation software. The graphics of the forklift model in Figure 9 were created in Blender software and the environment generated by Unity software. Figure 6 shows the flight map of the drone for the targeted area. The drone started flying from a specified spot and, after arriving at a specific height, it flew horizontally with a horizontal velocity of -20 km per hour while taking images. During its flight, the drone took approximately 1900 images with 80 percent overlap between continuous images. The percentage of the overlap can be defined by the controller before the flight. The maximum height that the drone flew was 50 m. Although in some photogrammetry procedures drones capture both radial and oblique images, in this case study, the drone captured radial images. The constructed 3D environment model is based on the nadiral images and point cloud, which is collected by the laser scanner. To collect the point cloud data, the operators relocated the laser scanner to certain predefined locations. The whole process took nearly three hours. The obtained images and the point cloud data were transferred to the Recap software to build the three-dimensional environment.