# Using Game Engines for Visuo-Haptic Learning Simulations
## 2 Related Work
### Unity and Haptic Devices  
The use of haptic devices in Unity can be found in different studies. In Medicine, [PERSON] et al. designed video laparoscopic training exercises and developed the eLaparo4D system [16]. The system eLaparo4D was constructed as a node.js application server, and it uses HTML5 with the Unity web engine plugin to give users an on-line platform. In the simulator, two Phantom Omni devices are used as tool handlers (grasper, hook or scissors) and a third one is used to move the camera within the virtual abdomen. To connect them, the authors used an in-house solution to add haptic interactivity in Unity. Another medical simulator is the one developed by [PERSON] et al. [17]. They created a virtual reality dental medicine training simulator. They used a Phantom Omni haptic to navigate and perform the tasks in the virtual scene. To enable haptic rendering, they used the Haptic Plug-In for Unity 5 [18], which is based on Geomagic's OpenHaptics software development kit (SDK) (Geomagic, Inc., Morrisville, NC). The simulator includes visual modifications and sound effects when medical procedures are performed in the oral cavity. In the area of myringotomy, which is a surgical incision into the eardrum, [PERSON] et al. implemented a VR-based environment to simulate all surgical aspects of myringotomy and tube placement [19]. The simulator uses a Phantom Omni haptic device for 3D positioning of surgical instruments, such as the virtual microscope, blade, and forceps. OpenHaptics SDK was also used for force rendering and positioning of the haptic device. Finally, the anatomical structures were modeled using the MIPAV (Medical Image Processing, Analysis, and Visualization) software package (Bethesda, MD) and Geomagic Studio (Geomagic, Inc., Morrisville, NC). [PERSON] et al. created a knee bone drilling simulator to examine the use of visuo-haptic virtual simulations as affordable training solutions [20; 21]. The authors implemented the simulation in Unity, and the simulator uses two haptic devices, a Novint Falcon and a Geomagic Touch. These are used to perform surgical drilling through bone in total knee arthroplasty. The authors used OpenHaptics SDK and the falconunity solution [22] to provide connectivity with the haptic devices of each brand. However, they do not mention if both devices can interact at the same time in the virtual environment. [PERSON] et al. developed a 3D immersive spatial cognition trainer with haptic interaction [23]. This simulator allows users to practice 3D manipulations through four levels of increasing difficulty. The aim of this study was to measure if mental rotation and visualization of viewpoints tests improve spatial abilities. The simulator was built using Unity and two Geomagic Touch haptic devices. The interaction with the haptic device is implemented through a custom plug-in the authors developed. Lastly, in the area of robotics, [PERSON] et al. developed a simulator to control an emulated manipulator with a haptic device [24]. The simulator allows performance analysis of different schemes in autonomous control, tele-operated control, or both. They developed it using Unity for graphics and MATLAB (MathWorks, MA, USA) for the control algorithms and connectivity with the haptic device. The authors used a Falcon haptic device to control the simulated robot arm. Virtual environments that incorporate haptic devices provide an important alternative for interactive training and learning environments. The above-presented simulators allow proper simulations; however, they usually are developed in long periods of time. Additionally, some studies only focus on functionality and leaves the improvement of visual realism as future work. On the other hand, current implementations only use game engines for visualization or only consider the use of one type of haptic device during simulation. Moreover, the falconunity solution requires older Falcon drivers. Moreover, it uses a server for connectivity in Unity if one does not have a professional edition.