Researches On Cutting Simulation Based On A Hybrid Model In The Virtual Surgery System

Virtual surgery system is a tool which uses technologies of simulation in computer graphics to recreate the scenes of surgery training. This system helps the surgeons to get familiar with the surgery procedure as well as to find the best solution. The cutting simulation algorithm studied in this paper is an important part of this training system. It provides a realtime and robust cutting simulation which fully satisfies the 31 Feature (Immersion, Imagination and Interaction) of a virtual surgery training system.In this thesis, the overall steps of the cutting simulation would be studied and presented. The research interests can be divided into four parts:(1) Construction of a hybrid model.The hybrid model used in this simulation is a combination of the traditional sur-face triangle mesh and the meshless model. There are two parts of domains that need to be maintained in this hybrid model. One part is a series of triangles which describe the contour of current object; the other part is a point set organized by meshless method that describes the inner information of the object. An adaptive method is used to calculate the inner point set automatically.(2) Collision detection and reaction.Collision detection part uses the popular AABB tree method. However, an as-sumption of the consistency on cutting time and space is introduced, which greatly promotes the efficiency of the original collision detection algorithm.(3) Establishment of a deformation model.In this thesis, the traditional mass spring system is adjusted to the hybrid model. Also, a relative restoring force is added to ensure the volume of original objects. This deformation model is built on a net structure which presents to be more stable than the regular structures used before.(4) Mesh splitting and reconstruction.Mesh splitting process can be divided into two steps. The first step is surface splitting, and the other step is the generation of the inner points. Surface splitting in this thesis is based on an edge-splitting method, while generation of the new points is based on the path tracing of the virtual tool. In order to maintain the mesh quality after cutting, some point modification methods are used before inserting new points.There are several innovation points in this thesis. Firstly, a novel hybrid mod-el which combines the meshless methods and the surface mesh is introduced as the foundation of our simulation methods. Secondly, the mass spring system is adjust-ed to the hybrid model for the first time, and this establishes the basic deformation model in simulation. Thirdly, a time-space consistency consumption which greatly improves the efficiency of collision detection is proposed. Finally, in the cutting part, an edge-splitting method is used to keep the consistency of the surface mesh and several point-based rules are used to keep the quality of the model after cutting.In addition, in order to ensure that current simulation algorithms could satisfy the efficiency requirement of a virtual surgery system, GPU calculation is used to ac-celerate some parts of the procedure. Simulation results of each step and efficiency evaluations of all the simulation algorithms are described in the experiment part.At the end of this thesis, simulation results in the virtual surgery system using our method are presented. Apparently, the method raised in this research could finely sustain the requirements of the virtual surgery system, but there are still some flaws that can be improved in the future.