From this flowchart, it can be seen that the laborious work is in creating the models in SMD format and the textures in VTF format. Figure 1 illustrates the process of modeling. Then, GUIStuidoMDL was used to compile all of the required files of the game-based VL. In the project described here, the texture files were created by VTFEdit. The contents of SMD files mainly include the vertex and texture information of the models. The SMD file format stores 3D models in ASCII format for analysis and compilation by StudioMDL. The traditional modeling approach is based on using built-in tools such as ‘Hammer’ or third-party software such as ‘3ds Max’ and ‘VTFEdit’ to generate the StudioMDL data (SMD) file and texture file. During the piloting of the game-based VL, it became apparent that real-time modeling of the physical objects in the virtual environment would be very desirable. In addition, this VL has been proved to be an efficient alternative to traditional hands-on laboratories. The resulting VL implementation here is immersive, distributed and collaborative. Generally, game engines provide the developers with various basic functions such as graphics rendering, sound generation, physics modeling, game logics, artificial intelligence, user interactions and networking. Garry’s Mod is a multi-player computer game modification of the ‘Source’ game engine. The VL presented here was implemented based on Garry’s Mod. At the same time, building ready-to-use models for games also requires a special pipeline. These software packages may each have advantages when used in specific applications, but the specific game environment used in the project described here requires a special format of the models. Software for 3D reconstruction includes ‘3DSOM Pro’ (for producing 3D models through a series of alignment pictures ), ‘ReconstructMeQt’ (for building 3D surfaces with Kinect and exporting 3D surface files into other software ), and ‘KinectFusion’ (for generating 3D models in real time with a Kinect camera ). For instance, methods for reconstructing 3D faces of people, for 3D voxel reconstruction of human motions and for 3D reconstruction of urban scenes from videos have been reported. the appearance of structured light cameras and the improvement of image processing algorithms, 3D reconstruction techniques have been boosted significantly. Second, the files used in the virtual environment. First, the conventional modeling method applied in Garry’s Mod was summarized and the steps of the proposed modeling approach for data acquisition and processing were discussed in detail. In this paper, a method for using the Kinect to create in real time custom models of physical objects for insertion into a game-based virtual environment was introduced. Although this model is not perfect, it is sufficient for the purpose of this experiment. Therefore, some points that do not belong to the model are included into the triangular domain. The reason for that is that the triangular domain becomes very large after simplifying the triangularization of the surfaces by merging some small triangles into one, which causes the curved edge in Figure 7 to become straight. In addition, some textures failed to be filtered, thus leaving a small part of the background in the reconstructed model. The textures were obtained from different surfaces with six orientations. The model of the motor is composed of several cuboids. The reason for doing so is that too many texture files would be generated by the basic Delaunay triangularization, but it is very difficult for the game engine to render such elaborate models. In this instance, the surface meshes were simplified significantly. This difference results from the resolution of the camera. The noticeable difference between the actual physical object and its reconstructed model is in the image quality. The step motor is represented with a coarse reconstructed model (see Figure 5b). Therefore, they were built with the traditional modeling pipeline (see Figure 1). In this virtual experimental setup, the test tube and its base are too large to be scanned with the method discussed here. A more detailed description of this experiment was given elsewhere. The Pitot tubes are controlled by step motors and are used to measure the pressure distributions at various cross sections of the test tube. It is composed of a test tube with base and multiple step motors and Pitot tubes. The experimental setup in the VL is illustrated in Figure 6. This experiment is used to teach the basic principles of fluid mechanics, and it focuses on the study of the flows in ducts and jets. The step motor is one of the components of a flow rig experiment. A step motor was selected as an example to validate the method described here (see Figure 5a). Mod/models folder and are available to be used by the game.
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