[SOUND] Hello this is week six of Interactive Computer Graphics. And the topic we'll discuss here is Computer-aided Design. So, computer-aided design is a process of designing products using computers. And today, almost all products are designed using computers. Starting from home electronics or garments, or cars, and houses. Everything is designed using a computer. And physics, plays an important role in here, and physics simulation is already heavily used in the design. However, in most cases currently, physics analysis is done after modeling. So user or designers design 3D model and the modelers CAD Operators design 3D model. And only after that, the model is transported into the physical simulation system, and then, the people will analyze the property like collision, friction, material property, gravity and so on. And if there's a problem, go back to the design. So, but this is useful for testing the validity afterwards, but this is not very good for actively use physics into the design process. So what we try to do here, is to integrate real-time physics into modeling. So, so currently 3D model ignore physics. Just specify x, y, z coordinates and shapes, but here in the system we introduce here. Are all integrates, 3D of physical simulation into the modeling process, so as user generates a model, of physical simulation automatically checks the validity and then provides feedbacks. So that's the basic idea. And then we will show a couple of example systems here. So, this is a list of topics we're discussing this week. So one is cantilever design for architecture. And design with music- novel musical instruments and garment design, furniture design and finally hobby glider design. So the first one is cantilever design. So this one is called responsive FEM, Finite Element Method, for aiding interactive geometric modeling. So the problem we want today- discuss here is design of a, physical thing with physical constraint. Here, as an example is a cantilever design. Suppose you have a vertical wall here. And then you have a horizontal steel bar attached to the wall. So originally, the steel bar is connected vertically com- completely horizontally, perpendicular to the wall. But after construction, if you release your hand, support material, gravity pulls the steel downwards. So, this is of course exaggerated. But in reality, there's always a deformation. So the goal is to find the shape that di- ended in a completely flat horizontal shape, after applying gravity. So this is a kind of difficult inverse problem. A typical approach is to run physical simulation after modeling. So, user specifies a rest shape and then physical simulation predicts what happens. Looking at the result, user go back to the design phase, and adjusts the shape and they go to a simulation. But this kind of back and forth interaction is not very efficient. So what we propose is to run physical simulation during modeling, specifically, while user is dragging mesh vertices one by one. System should continuously provide feedback. This way, you can just know when to release dragging. So let me show you a demonstration. So here is a demonstration. So left side is original rest shape. Then right side is after the gravity, is applied. And here, the simulation is continuous, as a user. So this is so natural, so smooth, it's very hard to see, but hard to appreciate. But, as a user drags a system continuously physical simulation and continuously presenting the deformed shape, after physical simulation, it's very, very fast. So as a user change, the position system continuously updates, runs many, many simulations. And then shows the simulation result. So it's so fast and so smooth, so user actually looking at this simulation result, while dragging. So simulation result is satisfactory, user just stop dragging, and you'll get the desired result. So, that's the result, and the algorithm we use here is a standard finite element simulation. So finite element simulation is to divide the domain, shape into small regions. In this case triangle regions. And then compute physical equations on this matrix on these systems. And then internally, this is a kind of many, many it's internally essentially it solves Huge linear equations, and actually handling matrices. And in order to accelerate this computation in this kind of direct manipulation editing, what we use, what we use is here. Reusing of intermediate computation results. So, traditionally it's too slow to hm- run this kind of physical simulation from scratch each, each frame. But in this example, in this modeling task, you know, you have the previous step for simulation result. And compared to the previous simulation result, current suffers only a slight change, you know? User is Dragging single vertex, the change is very small. So you can reuse most of the previous computation. So that's a topic trick we use, we use. Now, this is a little bit more details. So, of course it's not possible to explain everything, because we skipped the explanation of finite element method. It's a little bit complicated. But still, you can get the general idea. So left hand side uses a coefficient matrix a, pre-conditioned matrix x. So, we do not describe details about these other mesh- matrix structure we use in the computation of this simulation. And also, matrix has a value list and then structure, and the value list, and then structure. So these information are heavily used in the system. And construction, of this information is time consuming. So in the idle time, nothing happened, so we can reuse old intermediate structure. And in the during dragging, we divided the dragging depending on the distance. When the dragging operation is very small, very small relocation, then what's the system is do just updates the mash- mesh vertices. And almost all information will be used. As a user drags more and more, then, simple vertex relocation doesn't work, so system tries the update, while it finds a topology. But after a while, if the deformation still rise, then simple relocation and simple topology changes nothing now so system re- reconstructs the mesh. So this is what is happening, behind the scene, in this example. And internally, if the relocation is very small. Then only, system only, recomputes the value list of matrix A. And if you change the topology, you have to refresh all the coe- coef- coefficient matrix A. But you can still reuse the pre-condition matrix B. But after the reconstruction everything is re-computed. So this is equivalent to another simulation from scratch. But this happens very rarely. So this is a very short section, but summary is that we introduced cantilever design with concurrent physical simulation. So you can change rest shape while watching a simulation result. And internally, the most important point is that we apply multi-level reuse of intermediate computation result. More specifically internal large matrixes, matrices. For efficient computation. So original paper is available as Responsive FEM for Aiding Interactive Geometric Modeling. We discussed many other examples too there. And finite element method is an est- established method and there are many textbooks. One example is this one, the finite element method. Its basis and fundamentals. And structure optimization is often discussed in computer graphics. One example is this one. A procedure modeling of structurally sound masonry buildings. So this one is the kind of physics aware 3D modeling. However, there is also these just automatic optimization, and did not discuss interme- rapid feedback during user manipulation. Thank you.
