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5 Technological Platform

The serious game for laparoscopic suturing training was developed using OGRE 3D graphics engine [16], NVIDIA PhysX for physical modeling of the objects and HAPI library for haptic interactions and force feedback rendering.

PhysX [17] is a real-time physics simulation framework developed from NVIDIA. A major advantage of this physics engine is the support of hardware acceleration when a compatible Graphics Processing Unit is installed. Developers can instruct the engine to utilize the processing power of the GPU in order to perform physics computation and to relieve the CPU for other tasks.

PhysX uses a position-based approach for the body dynamics management in order to reduce the instability problems that could make unnatural the results of simulation and so the resulting environment [18].

The PhysX engine supports the simulation of both rigid bodies and soft objects, including cloth and fluids. It employs a scene graph to manage the objects in a virtual environment.

In order to provide a force feedback to the user, an haptic interface is used in our simulation. In our developed solution it is possible to use two SensAble Phantom Omni or two Novint Falcon haptic devices.

The choice of the preferred haptic devices is possible through the use of the multidevice HAPI library. This library has the advantage to be open-source and crossplatform. It supports many commercial haptic interface and the user can extend this compatibility writing its own library extension. In order to improve simulation results it is better to use two Phantom Omni devices that have a larger workspace and are provided of 6 DOFs [19].

6 Simulation Models

One of the most important thing in surgical simulation is the real-world reproduction fidelity. The reproduction fidelity is measured not only in terms of graphical rendering fidelity but also in terms of physical behaviours simulation. Objects and materials should react to forces and solicitation like in the real world.

To achieve this goal it is necessary to use a physically-based simulation. This approach considers the physical properties of the object materials as well as its geometrical shape in a mathematical model that tries to reproduce the real world. Generally more are real world reproduction fidelity constraints more computational resources are needed in order to obtain an accurate simulation. These constraints are generally in contrast with the requirement to have a "real-time" interactive simulation which can responds to the user interaction.

Fig. 1. Tissue modeling using the mass-spring method

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