15 research outputs found
IST Austria Thesis
Computer graphics is an extremely exciting field for two reasons. On the one hand,
there is a healthy injection of pragmatism coming from the visual effects industry
that want robust algorithms that work so they can produce results at an increasingly
frantic pace. On the other hand, they must always try to push the envelope and
achieve the impossible to wow their audiences in the next blockbuster, which means
that the industry has not succumb to conservatism, and there is plenty of room to
try out new and crazy ideas if there is a chance that it will pan into something
useful.
Water simulation has been in visual effects for decades, however it still remains
extremely challenging because of its high computational cost and difficult artdirectability.
The work in this thesis tries to address some of these difficulties.
Specifically, we make the following three novel contributions to the state-of-the-art
in water simulation for visual effects.
First, we develop the first algorithm that can convert any sequence of closed
surfaces in time into a moving triangle mesh. State-of-the-art methods at the time
could only handle surfaces with fixed connectivity, but we are the first to be able to
handle surfaces that merge and split apart. This is important for water simulation
practitioners, because it allows them to convert splashy water surfaces extracted
from particles or simulated using grid-based level sets into triangle meshes that can
be either textured and enhanced with extra surface dynamics as a post-process.
We also apply our algorithm to other phenomena that merge and split apart, such
as morphs and noisy reconstructions of human performances.
Second, we formulate a surface-based energy that measures the deviation of a
water surface froma physically valid state. Such discrepancies arise when there is a
mismatch in the degrees of freedom between the water surface and the underlying
physics solver. This commonly happens when practitioners use a moving triangle
mesh with a grid-based physics solver, or when high-resolution grid-based surfaces
are combined with low-resolution physics. Following the direction of steepest
descent on our surface-based energy, we can either smooth these artifacts or turn
them into high-resolution waves by interpreting the energy as a physical potential.
Third, we extend state-of-the-art techniques in non-reflecting boundaries to handle spatially and time-varying background flows. This allows a novel new
workflow where practitioners can re-simulate part of an existing simulation, such
as removing a solid obstacle, adding a new splash or locally changing the resolution.
Such changes can easily lead to new waves in the re-simulated region that would
reflect off of the new simulation boundary, effectively ruining the illusion of a
seamless simulation boundary between the existing and new simulations. Our
non-reflecting boundaries makes sure that such waves are absorbed
SIGGRAPH
We present a method for recovering a temporally coherent, deforming triangle mesh with arbitrarily changing topology from an incoherent sequence of static closed surfaces. We solve this problem using the surface geometry alone, without any prior information like surface templates or velocity fields. Our system combines a proven strategy for triangle mesh improvement, a robust multi-resolution non-rigid registration routine, and a reliable technique for changing surface mesh topology. We also introduce a novel topological constraint enforcement algorithm to ensure that the output and input always have similar topology. We apply our technique to a series of diverse input data from video reconstructions, physics simulations, and artistic morphs. The structured output of our algorithm allows us to efficiently track information like colors and displacement maps, recover velocity information, and solve PDEs on the mesh as a post process
Wave curves: Simulating Lagrangian water waves on dynamically deforming surfaces
We propose a method to enhance the visual detail of a water surface simulation. Our method works as a post-processing step which takes a simulation as input and increases its apparent resolution by simulating many detailed Lagrangian water waves on top of it. We extend linear water wave theory to work in non-planar domains which deform over time, and we discretize the theory using Lagrangian wave packets attached to spline curves. The method is numerically stable and trivially parallelizable, and it produces high frequency ripples with dispersive wave-like behaviors customized to the underlying fluid simulation
Fundamental solutions for water wave animation
This paper investigates the use of fundamental solutions for animating detailed linear water surface waves. We first propose an analytical solution for efficiently animating circular ripples in closed form. We then show how to adapt the method of fundamental solutions (MFS) to create ambient waves interacting with complex obstacles. Subsequently, we present a novel wavelet-based discretization which outperforms the state of the art MFS approach for simulating time-varying water surface waves with moving obstacles. Our results feature high-resolution spatial details, interactions with complex boundaries, and large open ocean domains. Our method compares favorably with previous work as well as known analytical solutions. We also present comparisons between our method and real world examples