## 3 Results and Discussion
### Proposition of a Method of Developing Immersive Metaverses for Industrial Training
#### 3.2.2 3D Modeling  
Understanding the project's goal is crucial to carrying out the industrial training project since it will help to estimate the degree of precision and detail needed for 3D modeling. 3D scanning and hard-surface modeling are two modeling methods that are frequently utilized in industrial training.  
3D scanning may be achieved using photogrammetry or lasers, allowing for the reconstruction of 3D models, although it typically contains a high quantity of polygons, which degrades performance. To address this issue, 3D object topology is a good choice for simplifying the model and making it suitable for more demanding game engines [30].  
Figure 3: Interactive scene developed in Unreal Engine 4.  
3D modeling can be divided into two main categories, which are organic modeling and hard-surface modeling [31]. Hard-surface models are usually with everything human-made or constructed items [13; 32], such as automobiles, robots, and other mechanical equipment, and may be accomplished using programs such as 3 ds Max, Sketchup, Maya, Modo, and Blender, among others. While organic modeling relates to characters, animals, trees, plants, and other living objects, hard-surface modeling consists of techniques that are used to make machines, vehicles, robots, weapons, and generally any non-living objects that have smooth, static surfaces [31]. Thus, if mechanical engineering is the focus, software such as SolidWorks, Inventor, and Catia, among others, can be used.  
3D objects are fundamental in the development of the virtual reality environment, and their quality can influence the user's perception of the virtual world [33]. Although engaging with the virtual world offers many opportunities for viewers, the performance of the current technology is severely constrained. The Meta Quest aims for 300,000-500,000 triangles and 150-175 draw calls per frame, compared to the Oculus Rift S's 1-2 million triangles and 500-1000 draw calls per frame [7]. Simply put, this implies that in order to maximize speed, the number of polygons in the 3D models had to be drastically reduced, and the quantity of materials, texture sizes, and lighting had to be optimized. The intricate drawings used to create the high-polygon-count 3D models were converted into a more common type of mesh, which was then remeshed and retopologized to lower the polygon count [7]. So, for an industrial training project, hard-surface modeling is the most appropriate choice. 3D scanning can be used to accelerate modeling, providing a point cloud as a reference. Using software like 3 ds Max 2022 or Blender 3.5 allows developers to optimize the model for mobile applications like Android and the Meta Quest 2 virtual reality device. It is important to note that we chose Meta Quest 2 due to its popularity and affordability, making it accessible to a wider audience. Additionally, Meta Quest 2 is compatible with the Unreal Engine software version 4.27.2, allowing us to test the proposed methodology in a real-world scenario.  
Hard-surface modeling was chosen and will be developed using Autodesk's 3 ds Max 2022 software. Figures 4 and 5 illustrate a modeled hydraulic press.  
Figure 4: Hydraulic Press digitizing process [34].