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1.
A topology preserving level set method for geometric deformable models   总被引:14,自引:0,他引:14  
Active contour and surface models, also known as deformable models, are powerful image segmentation techniques. Geometric deformable models implemented using level set methods have advantages over parametric models due to their intrinsic behavior, parameterization independence, and ease of implementation. However, a long claimed advantage of geometric deformable models-the ability to automatically handle topology changes-turns out to be a liability in applications where the object to be segmented has a known topology that must be preserved. We present a new class of geometric deformable models designed using a novel topology-preserving level set method, which achieves topology preservation by applying the simple point concept from digital topology. These new models maintain the other advantages of standard geometric deformable models including subpixel accuracy and production of nonintersecting curves or surfaces. Moreover, since the topology-preserving constraint is enforced efficiently through local computations, the resulting algorithm incurs only nominal computational overhead over standard geometric deformable models. Several experiments on simulated and real data are provided to demonstrate the performance of this new deformable model algorithm.  相似文献   

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We propose models of 3D shape which may be viewed as deformable bodies composed of simulated elastic material. In contrast to traditional, purely geometric models of shape, deformable models are active—their shapes change in response to externally applied forces. We develop a deformable model for 3D shape which has a preference for axial symmetry. Symmetry is represented even though the model does not belong to a parametric shape family such as (generalized) cylinders. Rather, a symmetry-seeking property is designed into internal forces that constrain the deformations of the model. We develop a framework for 3D object reconstruction based on symmetry-seeking models. Instances of these models are formed from monocular image data through the action of external forces derived from the data. The forces proposed in this paper deform the model in space so that the shape of its projection into the image plane is consistent with the 2D silhouette of an object of interest. The effectiveness of our approach is demonstrated using natural images.  相似文献   

4.
It is well known that reaction-diffusion systems describing Turing models can display very rich pattern formation behavior. Turing systems have been proposed for pattern formation in various biological systems, e.g. patterns in fish, butterflies, lady bugs and etc. A Turing model expresses temporal behavior of the concentrations of two reacting and diffusing chemicals which is represented by coupled reaction-diffusion equations. Since the base of these reaction-diffusion equations arises from the conservation laws, we develop a hybrid finite volume spectral element method for the numerical solution of them and apply the proposed method to Turing system generated by the Schnakenberg model. Also, as numerical simulations, we study the variety of spatio-temporal patterns for various values of diffusion rates in the problem.  相似文献   

5.
We investigate some hypersurface-homogeneous cosmological models in the presence of a dynamically anisotropic equation of state parameter and a dynamical energy density in general relativity. A general form of the anisotropy parameter is obtained to find a hypothetical fluid with an anisotropic equation of state. Exact solutions of Einstein’s field equations are obtained by assuming two different volume expansion laws. Geometric and kinematic properties of the models and the behavior of the anisotropy of dark energy are discussed in detail.  相似文献   

6.
Online Remeshing for Soft Tissue Simulation in Surgical Training   总被引:1,自引:0,他引:1  
Surgical simulation is a graphical application that requires real-time interaction with deformable 3D objects. A surgical training system must allow the trainee to interact with virtual soft tissue. Therefore, the challenging task is to develop efficient models of living tissues so that the realistic simulation of tool-tissue interaction can be performed in real time. To graphically model and animate the realistic behavior of deformable tissue in surgical simulations, the authors' system adapts tetrahedra resolution by dynamically retessellating the mesh in and around the regions of interest. This technique overcomes limitations of previous methods that made it difficult to modify the mesh's topology online  相似文献   

7.
A fluid-based soft-object model   总被引:2,自引:0,他引:2  
Physically based modeling is a computer animation technique that simulates dynamic objects to a high degree of realism. Central to the technique is the process of solving a set of differential equations that express laws from classical mechanics. In this article, we introduce a new physically based method for modeling and animating soft deformable objects.  相似文献   

8.
We investigate the asymptotic behavior of a cosmological model based on a phantom scalar field by qualitative analysis of the set of differential equations. We show that, as opposed to models with a classical scalar field, such models have stable asymptotic solutions with a constant value of the potential both in the infinite past and the infinite future. We also develop numerical models of the cosmological evolution with a phantom scalar field.  相似文献   

9.
A new computer haptics algorithm to be used in general interactive manipulations of deformable virtual objects is presented. In multimodal interactive simulations, haptic feedback computation often comes from contact forces. Subsequently, the fidelity of haptic rendering depends significantly on contact space modeling. Contact and friction laws between deformable models are often simplified in up to date methods. They do not allow a "realistic" rendering of the subtleties of contact space physical phenomena (such as slip and stick effects due to friction or mechanical coupling between contacts). In this paper, we use Signorini's contact law and Coulomb's friction law as a computer haptics basis. Real-time performance is made possible thanks to a linearization of the behavior in the contact space, formulated as the so-called Delassus operator, and iteratively solved by a Gauss-Seidel type algorithm. Dynamic deformation uses corotational global formulation to obtain the Delassus operator in which the mass and stiffness ratio are dissociated from the simulation time step. This last point is crucial to keep stable haptic feedback. This global approach has been packaged, implemented, and tested. Stable and realistic 6D haptic feedback is demonstrated through a clipping task experiment.  相似文献   

10.
力/触觉再现技术的出现,为虚拟现实开辟了全新的应用领域,促使基于物理意义的柔性物体形变建模成为一个研究热点.系统地讨论了近年来基于物理意义的柔性物体形变建模方法,分析了基于直接构建的模型、基于连续介质力学的模型和其他相关模型的基本思想和优缺点.对这些建模方法的性能进行了细致的比较,并探讨了柔性物体物理形变建模的未来发展趋势.  相似文献   

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