Browsing by Author "Borer, Dominik"

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    Differentiable Simulation for Outcome-Driven Orthognathic Surgery Planning
    (The Eurographics Association and John Wiley & Sons Ltd., 2022) Dorda, Daniel; Peter, Daniel; Borer, Dominik; Huber, Niko Benjamin; Sailer, Irena; Gross, Markus; Solenthaler, Barbara; Thomaszewski, Bernhard; Dominik L. Michels; Soeren Pirk
    Algorithms at the intersection of computer graphics and medicine have recently gained renewed attention. A particular interest are methods for virtual surgery planning (VSP), where treatment parameters must be carefully chosen to achieve a desired treatment outcome. FEM simulators can verify the treatment parameters by comparing a predicted outcome to the desired one. However, estimating the optimal parameters amounts to solving a challenging inverse problem. In current clinical practice it is solved manually by surgeons, who rely on their experience and intuition to iteratively refine the parameters, verifying them with simulated predictions. We prototype a differentiable FEM simulator and explore how it can enhance and simplify treatment planning, which is ultimately necessary to integrate simulation-based VSP tools into a clinical workflow. Specifically, we define a parametric treatment model based on surgeon input, and with analytically derived simulation gradients we optimise it against an objective defined on the visible facial 3D surface. By using sensitivity analysis, we can easily explore the solution-space with first-order approximations, which allow the surgeon to interactively visualise the effect of parameter variations on a given treatment plan. The objective function allows landmarks to be freely chosen, accommodating the multiple methodologies in clinical planning. We show that even with a very sparse set of guiding landmarks, our simulator robustly converges to a feasible post-treatment shape.
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    Keys-to-Sim: Transferring Hand-Crafted Key-framed Animations to Simulated Figures using Wide Band Stochastic Trajectory Optimization
    (The Eurographics Association, 2018) Borer, Dominik; Guay, Martin; Sumner, Robert W.; {Tam, Gary K. L. and Vidal, Franck
    The vision of fully simulating characters and their environments has the potential to offer rich interactions between characters and objects in the virtual world. However, this introduces a challenging problem similar to controlling robotic figures: computing the necessary torques to perform a given task. In this paper, we address the problem of transferring hand-crafted kinematic motions to a fully simulated figure, by computing open-loop controls necessary to reproduce the target motion. One key ingredient to successful control is the mechanical feasibility of the target motion. While several methods have been successful at replicating human captured motion, there has not yet been a method capable of handling the case of artist-authored key-framed movements that can violate the laws of physics or go beyond the mechanical limits of the character. Due to the curse of dimensionality, sampling-based optimization methods typically restrict the search to a narrow band which limits exploration of feasible motions—resulting in a failure to reproduce the desired motion when a large deviation is required. In this paper, we solve this problem by combining a window-based breakdown of the controls on the temporal dimension, together with a global wide search strategy that keeps locally sub-optimal samples throughout the optimization.