Improved surface model particle spring modeling can be seen that the result of force action is the result of force action, and the source of force, in addition to external force, is mainly due to the elasticity of the spring. The different spring layouts have different forces on the particles, and the trajectories of the particles are different, resulting in different deformation effects. If the spring structure is unreasonable, when the external force acts, the spring model not only can not simulate the soft tissue deformation well, and sometimes it is beyond recognition, leading to collapse. Therefore, one of the keys to the simulation of soft tissue deformation using the particle spring model is how to establish the topology of the spring. In the real-time simulation of fabrics, three types of springs are generally used. Structural springs express structural stress, shear springs exhibit shear stress, and flexible springs express fabric deflection.
Dynamic local refinement of the model Generally speaking, the model with higher resolution (the number of triangles), whether it is drawing or deformation simulation, should be the initial position of the particle deformation position surface spring virtual body if the calculation time is not considered. The direction of the spring force is the virtual body spring.
This has a good visual effect. But when the resolution reaches a certain height, the visual difference may not be obvious. Conversely, if the resolution is low, the effect of the rendering or deformation simulation will be very large or even completely distorted compared to the actual one. In addition, the resolution is proportional to the calculation time. If you want a good visual effect, you need to pay a higher calculation cost. However, for real-time application problems, the calculation time should be minimized. Therefore, we must balance between resolution and real-time. A kind of adaptive algorithm is an ideal method to balance this problem, that is, select the model with the appropriate resolution as the basic model, and then improve the resolution of the model in the local part that is interested or dynamically selected according to certain criteria, thus enhancing the real rendering. Sensitivity of the sense or simulation. Appropriate resolution refers to a lower resolution under the premise of the problem, in order to reduce the overhead of real-time calculation as much as possible to ensure the real-time requirements of the problem.
Surface mesh subdivision Surface mesh subdivision is one of the important methods for surface modeling in computer graphics. The subdivision can be either an approximation or an interpolation. The result of the subdivision is a smooth surface that is getting closer to its extreme position. The approximation algorithm is based on B-spline, so the resulting subdivision surface is contracted relative to the low-resolution surface, which destroys the position of the original point. The position of the original point is not on the surface after subdivision, and is not suitable for fine The soft tissue deformation surface model is divided.
Taking the spherical surface model as an example, the conventional particle spring modeling and the improved particle spring modeling of soft tissue deformation simulation were compared. The effect of the two models in each figure on the stress and the deformation after release. Tests have shown that, by conventional methods, the surface deformation is large after an external force is applied, and the original shape cannot be restored after the external force is removed. After applying the same external force, the spherical surface model is like an entity. It is very volumey and flexible, and the surface deformation is almost completely restored after the external force is removed. If you stretch it, it will have the same effect.
Although the basic model mesh is sparse, the dynamic local subdivision algorithm increases the resolution of the model locally near the point where the stress is concentrated, so that the accuracy of the soft tissue physical deformation simulation is improved without increasing the amount of calculation. . The use of a surface model to approximate the soft tissue has certain limitations, and needs further improvement to enhance the realism. There is still a lot of work to be done in the future, from the face model that approximates the body model to the real body model. At the same time, the idea of ​​dynamic modeling is extended to the volume model, and it is combined with the more accurate physical modeling method FEM (Finite Element Method) to make the FEM method calculate the accurate advantages and enhance its real-time performance. On the basis of the physical modeling deformation simulation of the surface model or the volume model, the simulation of the capsule incision and the capsulorhexis process is realized by means of the force feedback device.
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