Tracking, correcting and absorbing water surface waves Dissertation Thesis


Author(s): Bojsen-Hansen, Morten
Advisor(s): Wojtan, Chris
Committee Chair(s): Shigemoto, Ryuichi
Committee Member(s): Li, Hao; Thürey, Nils; Kolmogorov, Vladimir
Title: Tracking, correcting and absorbing water surface waves
Affiliation IST Austria
Abstract: 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.
Publication Title: IST Dissertation
Degree Granting Institution: IST Austria  
Degree: PhD
Degree Date: 2016-07-15
Start Page: 1
Total Pages: 114
URL:
DOI: 10.15479/AT:ISTA:th_640
Notes: First and foremost I would like to thank Chris. I have been incredibly lucky to have you as my advisor. Your integrity and aspiration to do the right thing in all walks of life is something I admire and aspire to. I also really appreciate the fact that when working with you it felt like we were equals. I think we had a very synergetic work relationship: I learned immensely from you, but I dare say that you learned a few things from me as well. ;) Next, I would like to thank my amazing committee. Hao, it was a fantastic experience working with you. You showed me how to persevere and keep morale high when things were looking the most bleak before the deadline. You are an incredible motivator and super fun to be around! Vladimir, thanks for the shared lunches and the poker games. Sorry for not bringing them back when I got busy. Also, sorry for embarrassing you by asking about your guitar playing that one time. You really are quite awesome! Nils, one of the friendliest and most humble people you will meet and a top notch researcher to boot! Thank you for joining my committee late! I would also like to acknowledge the Visual Computing group at IST Austria from whom I have learned so much. The excellent discussions we had in reading groups and research meetings really helped me become a better researcher! Next, I would like to thank all the amazing people that I met during my PhD studies, both at IST Austria, in Vienna and elsewhere.
Open access: yes (repository)
IST Austria Authors
  1. Chris Wojtan
    33 Wojtan
  2. Ryuichi Shigemoto
    237 Shigemoto
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