Biography

I am currently a Ph.D. cadidate in computer science department in University of Southern California under the guidence of Prof. Jernej Barbič. My research interest is computer graphics. Before coming to USC, I was an undergraduate in the Department of Computer Science and Technology in Tsinghua University, Beijing, China.

Education

Ph.D. Candidatein Computer Science, University of Southern California2014 - present
Undergraduate in Computer Science and Technology, Tsinghua University 2010 - 2014

Publications

Evaluating the Efficiency of Six-DoF Haptic Rendering-Based Virtual Assembly Training

Mianlun Zheng, Danyong Zhao,Jernej Barbič
Transactions on Haptics, 2000, awaiting final publication, doi: 10.1109/TOH.2020.3008941.

Haptics plays an important role in training users to assemble mechanical components such as airplane or car parts. Because mechanical components are often geometrically complex, efficient collision detection and 6-DoF haptic rendering of contact are required for virtual assembly, and this has been extensively explored in prior work. However, as our work shows, this alone is not sufficient for efficient virtual assembly training. Our work asks how to augment 6-DoF haptic rendering of contact to maximize virtual assembly training efficiency, and proposes and measures several visual and haptic guidance strategies. Our visual strategies consist of displaying animations of the correct assembly path, motion indicator cues, and close-ups on difficult assembly path sections. Our haptic guidance consists of forces and torques that correct the trainee's deviation from the path. We investigate several haptic guidance strategies, including continuous forces and torques, force/torque nudging and anti-forces/torques. We designed a user study to evaluate the training efficiency of our proposed strategies quantitatively, using ANOVA and Tukey statistics. Our main finding is that the most efficient training approach is to use haptic rendering of contact in combination with visual animation-based guidance. Continuous forces, nudging, anti-forces and motion indicator cues were measured to be less effective.

[project page] [paper 13.3 Mb] [video 39.1 Mb] [bibtex]

6-DoF Haptic Rendering of Static Coulomb Friction Using Linear Programming

Danyong Zhao,Yijing Li, Jernej Barbič
IEEE Transactions on Haptics 2018, 11(3), 2018.

Simulating frictional contact between objects with complex geometry is important for 6-DoF haptic rendering applications. For example, friction determines whether components can be navigated past narrow clearances in virtual assembly. State-of-the-art haptic rendering of frictional contact either augments penalty contact with frictional penalty springs, which do not prevent sliding and cannot render correct static friction, or uses constraint-based methods that have difficulties in meeting the stringent haptic loop computation time requirements for complex geometry. We give a 6-DoF Coulomb friction haptic rendering algorithm for distributed contact between rigid objects with complex geometry. Our algorithm is compatible with the fast point vs implicit function penalty-based contact method such as the Voxmap-PointShell method. Our algorithm incorporates the maximal dissipation principle and produces correct static friction, all the while inheriting the speed of penalty-based methods. We demonstrate our algorithm on several challenging 6-DoF haptic rendering examples.

[project page] [paper 9 Mb] [video 141 Mb] [bibtex]

Asynchronous Implicit Backward Euler Integration

Danyong Zhao,Yijing Li, Jernej Barbič
Symposium on Computer Animation (SCA) 2016, Zurich, Switzerland.

In standard deformable object simulation in computer animation, all the mesh elements or vertices are timestepped synchronously, i.e., under the same timestep. Previous asynchronous methods have been largely limited to explicit integration. We demonstrate how to perform spatially-varying timesteps for the widely popular implicit backward Euler integrator. Spatially-varying timesteps are useful when the object exhibits spatially-varying material properties such as Young's modulus or mass density. In synchronous simulation, a region with a high stiffness (or low mass density) will force a small timestep for the entire mesh, at a great computational cost, or else, the motion in the stiff (or low mass density) region will be artificially damped and inaccurate. Our method can assign smaller timesteps to stiffer (or lighter) regions, which makes it possible to properly resolve (sample) the high-frequency deformable dynamics arising from the stiff (or light) materials, resulting in greater accuracy and less artificial damping. Because soft (or heavy) regions can continue using a large timestep, our method provides a significantly higher accuracy under a fixed computational budget.

[project page] [paper 4.1M] [video 23M] [slides 25M] [bibtex]

Anisotropic Spherical Gaussians

Kun Xu, Wei-Lun Sun, Zhao Dong, Dan-Yong Zhao, Run-Dong Wu, Shi-Min Hu
ACM Transactions on Graphics 32(6), 209:1 - 209:11, 2013. (Proceedings of SIGGRAPH Asia 2013).

We present a novel Anisotropic Spherical Gaussian (ASG) function, built upon the Bingham distribution [Bingham 1974], which is much more effective and efficient in representing anisotropic spherical functions than Spherical Gaussians (SGs). In addition to retaining many desired properties of SGs, ASGs are also rotationally invariant and capable of representing all-frequency signals. To further strengthen the properties of ASGs, we have derived approximate closed-form solutions for their integral, product and convolution operators, whose errors are nearly negligible, as validated by quantitative analysis. Supported by all these operators, ASGs can be adapted in existing SG-based applications to enhance their scalability in handling anisotropic effects. To demonstrate the accuracy and efficiency of ASGs in practice, we have applied ASGs in two important SG-based rendering applications and the experimental results clearly reveal the merits of ASGs.

[project page] [paper 2.3M] [supplemental 1.7M] [slides 16.5M][video 45.8M] [bibtex]

Working Experience

Teaching

Teaching Assistant at University of Southern California

CSCI 570: Analysis of AlgorithmsSpring 2016 & Fall 2020
CSCI 585: Database SystemsSpring 2018 ~ Spring 2020
CSCI 520: Computer Animation and SimulationSpring 2017
CSCI 420: Computer GraphicsSpring 2015