3D Cloth Simulation

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# 3D Cloth Simulation - PowerPoint PPT Presentation

3D Cloth Simulation. Eva Schiffer Aaron Bryden. Goal. Learn about methods of 3D cloth simulation Implement a simulation with: point masses and a simple spring system the choice of explicit, and implicit integration. Existing methods, springs. Cloth is modeled as a system of point masses

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Presentation Transcript
3D Cloth Simulation
• Eva Schiffer
• Aaron Bryden
Goal
• Learn about methods of 3D cloth simulation
• Implement a simulation with:
• point masses and a simple spring system
• the choice of explicit, and implicit integration
Existing methods, springs
• Cloth is modeled as a system of point masses
• All springs use the same force equation
• Three types of springs:
• structural springs
• sheer springs
• bend springs

Equations from Steve RotenBerg’s Class’s notes

Existing methods,explicit integration
• set time step, s
• use state(t + s) = state(t) + s * forces(state(t), t)
• the state includes position and velocity
• must calculate each step by s
• good: simple to implement, okay for very high damping factors
• bad: slow, needs short s and/or high damping or it will “explode”
Existing methods, implicit integration
• use state(t + s) = state(t) + s * forces(state(t+s), t+s) or
• This means that we have to solve for values of deltax and deltav
• Uses modified conjugate gradient solver that exploits the sparsity that results from each node only being connect to nearby nodes.
What we did
• Basic spring forces
• particle system and simple explicit integration with generative forces inspired by “Particle System Dynamics” from SIGRAPH 2003 course notes
• Implicit Integration based on “Large Steps in Cloth Simulation” by Baraff and Witkin, 1998.
• Extended particle system and wrote implicit integration based on Hamilton Chong’s Code. Specifically, using his modified conjugate gradient solver and his filling of the df_dx and df_dy matrices based on position and velocity to have the proper sparsity characteristics.
Results
• Explicit is slow to calculate, due to requiring a very small time step, and requires tuning the time step depending on the spring constants and damping factors to keep it from degenerating into chaos
• Implicit is fast and does not degenerate with as small of a timestep. Each step takes longer to calculate, but the degree to which large time steps may be taken results in a significant time reduction to simulate a certain amount of time.