Kavan, Ladislav
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Publication A Simple Method for Correcting Facet Orientations in Polygon Meshes Based on Ray Casting(2014-10-01) Takayama, Kenshi; Jacobson, Alec; Kavan, Ladislav; Sorkine-Hornung, OlgaWe present a method for fixing incorrect orientations of facets in an input polygon mesh, a problem often seen in popular 3D model repositories, such that the front side of facets is visible from viewpoints outside of a solid shape represented or implied by the mesh. As opposed to previously proposed methods which are rather complex and hard to reproduce, our method is very simple, only requiring sampling visibilities by shooting many rays. We also propose a simple heuristic to handle interior facets that are invisible from exterior viewpoints. Our method is evaluated extensively with the SHREC’10 Generic 3D Warehouse dataset containing 3168 manually designed meshes, and is demonstrated to be very effective.Publication Basis Enrichment and Solid-Fluid Coupling for Model-Reduced Fluid Simulation(2015-03-01) Gerszewski, Dan; Kavan, Ladislav; Sloan, Peter-Pike; Bargteil, Adam W.We present several enhancements to model-reduced fluid simulation that allow improved simulation bases and twoway solid-fluid coupling. Specifically, we present a basis enrichment scheme that allows us to combine data driven or artistically derived bases with more general analytic bases derived from Laplacian Eigenfunctions. We handle two-way solid-fluid coupling in a time-splitting fashion— we alternately timestep the fluid and rigid body simulators, while taking into account the effects of the fluid on the rigid bodies and vice versa. We employ the vortex panel method to handle solid-fluid coupling and use dynamic pressure to compute the effect of the fluid on rigid bodies.Publication Projective Dynamics: Fusing Constraint Projections for Fast Simulation(2014-07-01) Bouaziz, Sofien; Martin, Sebastian; Liu, Tiantian; Kavan, Ladislav; Pauly, MarkWe present a new method for implicit time integration of physical systems. Our approach builds a bridge between nodal Finite Element methods and Position Based Dynamics, leading to a simple, efficient, robust, yet accurate solver that supports many different types of constraints. We propose specially designed energy potentials that can be solved efficiently using an alternating optimization approach. Inspired by continuum mechanics, we derive a set of continuumbased potentials that can be efficiently incorporated within our solver. We demonstrate the generality and robustness of our approach in many different applications ranging from the simulation of solids, cloths, and shells, to example-based simulation. Comparisons to Newton-based and Position Based Dynamics solvers highlight the benefits of our formulation.Publication Ambient Obsurance Baking on the GPU(2013-01-01) Sloan, Peter-Pike; Tranchida, Jason; Chen, Hao; Kavan, LadislavAmbient Occlusion and Ambient Obscurance are coarse approximations to global illumination from ambient lighting, commonly used in film and games. This paper describes a system that computes Ambient Obscurance over the vertices of complex polygon meshes. Novel contributions include pre-processing necessary for “triangle soup” scene representations to minimize artifacts, a compact model for different classes of instanced decorator objects such as trees and shrubs, a compact model for pre-computed visibility to be used on dynamically placed objects, and an approximation to model the occlusion of small decorator objects when ray tracing.Publication Robust Inside-Outside Segmentation Using Generalized Winding Numbers(2013-07-01) Jacobson, Alec; Kavan, Ladislav; Sorkine-Hornung, OlgaSolid shapes in computer graphics are often represented with boundary descriptions, e.g. triangle meshes, but animation, physicallybased simulation, and geometry processing are more realistic and accurate when explicit volume representations are available. Tetrahedral meshes which exactly contain (interpolate) the input boundary description are desirable but difficult to construct for a large class of input meshes. Character meshes and CAD models are often composed of many connected components with numerous selfintersections, non-manifold pieces, and open boundaries, precluding existing meshing algorithms. We propose an automatic algorithm handling all of these issues, resulting in a compact discretization of the input’s inner volume. We only require reasonably consistent orientation of the input triangle mesh. By generalizing the winding number for arbitrary triangle meshes, we define a function that is a perfect segmentation for watertight input and is well-behaved otherwise. This function guides a graphcut segmentation of a constrained Delaunay tessellation (CDT), providing a minimal description that meets the boundary exactly and may be fed as input to existing tools to achieve element quality. We highlight our robustness on a number of examples and show applications of solving PDEs, volumetric texturing and elastic simulation.Publication Consistently Orienting Facets in Polygon Meshes by Minimizing the Dirichlet Energy of Generalized Winding Numbers(2014-01-01) Takayama, Kenshi; Jacobson, Alec; Kavan, Ladislav; Sorkine-Hornung, OlgaJacobson et al. [JKSH13] hypothesized that the local coherency of the generalized winding number function proposed in that work could be used to correctly determine consistent facet orientations in polygon meshes. We report on an approach to consistently orienting facets in polygon meshes by minimizing the Dirichlet energy of generalized winding numbers. While the energy can be concisely formulated and efficiently computed, we found that this approach is fundamentally flawed and is unfortunately not applicable for most handmade meshes shared on popular mesh repositories such as Google 3D Warehouse.Publication Ink-and-Ray: Bas-Relief Meshes for Adding Global Illumination Effects to Hand-Drawn Characters(2014-03-01) Sýkora, Daniel; Kavan, Ladislav; Čadík, Martin; Jamriška, Ondřej; Jacobson, Alec; Whited, Brian; Simmons, Maryann; Sorkine-Hornung, OlgaWe present a new approach for generating global illumination renderings of hand-drawn characters using only a small set of simple annotations. Our system exploits the concept of bas-relief sculptures, making it possible to generate 3D proxies suitable for rendering without requiring side-views or extensive user input. We formulate an optimization process that automatically constructs approximate geometry sufficient to evoke the impression of a consistent 3D shape. The resulting renders provide the richer stylization capabilities of 3D global illumination while still retaining the 2D handdrawn look-and-feel. We demonstrate our approach on a varied set of handdrawn images and animations, showing that even in comparison to ground truth renderings of full 3D objects, our bas-relief approximation is able to produce convincing global illumination effects, including self-shadowing, glossy reflections, and diffuse color bleeding.Publication Anatomy Transfer(2013-11-01) Ali-Hamadi, Dicko; Liu, Tiantian; Gilles, Benjamin; Kavan, Ladislav; Faure, Francois; Palombi, Olivier; Cani, Marie-PauleCharacters with precise internal anatomy are important in film and visual effects, as well as in medical applications. We propose the first semi-automatic method for creating anatomical structures, such as bones, muscles, viscera and fat tissues. This is done by transferring a reference anatomical model from an input template to an arbitrary target character, only defined by its boundary representation (skin). The fat distribution of the target character needs to be specified. We can either infer this information from MRI data, or allow the users to express their creative intent through a new editing tool. The rest of our method runs automatically: it first transfers the bones to the target character, while maintaining their structure as much as possible. The bone layer, along with the target skin eroded using the fat thickness information, are then used to define a volume where we map the internal anatomy of the source model using harmonic (Laplacian) deformation. This way, we are able to quickly generate anatomical models for a large range of target characters, while maintaining anatomical constraints.Publication Sound Localization and Multi-Modal Steering for Autonomous Virtual Agents(2014-01-01) Huang, Pengfei; Wang, Yu; Kavan, Ladislav; Kapadia, Mubbasir; Badler, Norman IWith the increasing realism of interactive applications, there is a growing need for harnessing additional sensory modalities such as hearing. While the synthesis and propagation of sounds in virtual environments has been explored, there has been little work that addresses sound localization and its integration into behaviors for autonomous virtual agents. This paper develops a framework that enables autonomous virtual agents to localize sounds in dynamic virtual environments, subject to distortion effects due to attenuation, reflection and diffraction from obstacles, as well as interference between multiple audio signals. We additionally integrate hearing into standard predictive collision avoidance techniques and couple it with vision to allow agents to react to what they see and hear, while navigating in virtual environments.