Christopher Batty

Banting Postdoctoral Fellow,
Columbia Computer Graphics Group, Columbia University

E-mail: christopherbatty@yahoo.com

Recent news:
I finally posted some 3D sample code for my 2008 SCA paper on viscous liquids on GitHub. (March 29, 2013)
I posted my work-in-progress non-manifold, mixed dimensional point/segment/tri/tet simplicial mesh library to GitHub.
Our paper on Discrete Viscous Sheets has been conditionally accepted to SIGGRAPH 2012. (March 28, 2012)
A recent New Scientist article discusses icicle formations, and mentions our ongoing work with U of T's Stephen Morris towards simulating them. (Dec 31, 2011)
I have been named a Banting Postdoctoral Fellow. (Sept 15, 2011)
Our Perspective article (Computational Physics in Film) appeared in Science today. (Dec 24, 2010)

About me:

I do research in computer graphics and computational physics. My primary focus is fluid animation, although I am more broadly interested in applying physics as a fundamental tool in generating motion of all kinds. In my work, I strive to design algorithms that are based on sound physical, mathematical, and geometric principles, while being amenable to efficient and robust implementation.

Among other projects, I have developed methods for...

interactions between dynamic objects and fluids
animating and representing thin splashes and droplets
viscous liquids that coil and fold when poured (honey, syrup, etc.)
surface tension phenomena

Personal experience in visual effects has motivated much of my research: I have worked with Frantic Films (now Prime Focus VFX), Weta Digital (makers of Avatar and Lord of the Rings), and Exocortex Technologies. I am credited on the movie Superman Returns, and also worked on Scooby Doo 2: Monsters Unleashed and Wes Craven's Cursed. Aspects of my research are now deployed in fluid animation tools by Side Effects Software, Exotic Matter, Exocortex Technologies, and DPIT.

I am currently a postdoc at Columbia University working with Eitan Grinspun. I also manage the Physics-Based Animation blog, which has catalogued papers, people, and software in this field since 2007.

Animations:

run-length encoding for sparse fluid simulation

Publications:

	Discrete Viscous Sheets C. Batty, A. Uribe, B. Audoly, & E. Grinspun. Conditionally accepted to ACM SIGGRAPH 2012. A method for animating thin sheets of highly viscous liquid, drawing on and extending techniques from the simulation of thin shells and cloth. [PDF] [Project] [Video]
	A Simple Finite Volume Method for Adaptive Viscous Liquids C. Batty & B. Houston. ACM SIGGRAPH/Eurographics Symposium on Computer Animation 2011. An Eulerian approach to achieve higher detail animations of high viscosity liquid behaviour (buckling, coiling, etc.) on structured tetrahedral meshes. [PDF] [Video]
	A Simple Finite Difference Method for Time-Dependent, Variable Coefficient Stokes Flow on Irregular Domains C. Batty & R. Bridson [arXiv preprint]
	Computational Physics in Film R. Bridson & C. Batty. Science 330(6012): 1756-1757. A perspective piece on the increasingly common use of physical simulation in visual effects for film, along with discussion of some major challenges that remain. [PDF] [Journal]
	Simulating Viscous Incompressible Fluids with Embedded Boundary Finite Difference Methods C. Batty. PhD Thesis, University of British Columbia. [PDF] [Thesis Repository]
	Matching Fluid Simulation Elements to Surface Geometry and Topology T. Brochu, C. Batty, & R. Bridson. ACM SIGGRAPH 2010 (Transactions on Graphics, 29(4), 2010). By adding simulation degrees of freedom exactly where they provide the most benefit, and using a triangle mesh-based surface representation, we show how to achieve much greater detail in liquid animations. [PDF] [Project] [Journal]
	Tetrahedral Embedded Boundary Methods for Accurate and Flexible Adaptive Fluids C. Batty, S. Xenos, & B. Houston. Eurographics 2010 (Computer Graphics Forum, 29(2), 2010). This paper demonstrates that combining embedded boundary methods with tetrahedra-based fluid simulation enables spatially adaptive liquid simulation with more accurate enforcement of air and solid boundary conditions. [PDF] [Project] [Journal]
	Accurate Viscous Free Surfaces for Buckling, Coiling and Rotating Liquids C. Batty & R. Bridson. ACM SIGGRAPH/Eurographics Symposium on Computer Animation 2008. A simple method to enforce physically correct forces at the surface of viscous liquids, which in turn lets us reproduce previously very difficult effects like buckling, coiling, and rotational motion. [PDF] [Project] [Journal]
	A Fast Variational Framework for Accurate Solid-Fluid Coupling C. Batty, F. Bertails, & R. Bridson. ACM SIGGRAPH 2007 (Transactions on Graphics, 26(3), 2007). An optimization-based framework for accurately incorporating irregularly shaped rigid objects into standard grid-based fluid simulations, eliminating spurious "stairstep" artifacts and leakage that plagued previous methods. [PDF] [Project] [Journal]
	Hierarchical RLE Level Set: A Compact and Versatile Deformable Surface Representation B. Houston, M. Nielsen, C. Batty, O. Nilsson, & K. Museth. ACM Transactions on Graphics, 25(1), 2006. A compressed representation of level set implicit surfaces that avoids storing and processing irrelevant data far from the surface itself, allowing more efficient treatment of operations like morphing and liquid surface tracking. [PDF] [Project] [Journal]

Sketches:

	Visual Simulation of Wispy Smoke C. Batty & B. Houston. ACM SIGGRAPH Sketches, 2005. A description of the smoke simulation techniques used on Wes Craven's werewolf movie Cursed. [PDF] [Project] [Journal]
	Gigantic Deformable Surfaces B. Houston, M. Nielsen, C. Batty, O. Nilsson, & K. Museth. ACM SIGGRAPH Sketches, 2005. A preview of the HRLE level set described more fully in the TOG paper above. [PDF] [Project] [Journal]
	RLE Sparse Level Sets B. Houston, M. Wiebe, & C. Batty. ACM SIGGRAPH Sketches, 2004. A compressed level set representation that was the precursor to the eventual HRLE level set above. [PDF] [Project] [Journal]

Teaching:

Notes on Fluids: An introduction to Eulerian fluid animation for computer graphics.
Part One PPTX PDF
Part Two PPTX PDF

Code and Data:

Miscellaneous sample code and data from some of my projects. I'd love to hear from you if you find any of this useful.

Non-manifold Simplicial Complex Mesh Library This is my own implementation of a non-manifold simplicial complex-based mesh library, including arbitrary data associated to vertices, edges, triangles and tetrahedra. It's essentially my spin on the data structure outlined in "Building Your Own DEC at Home" with an API similar to "Design, Implementation, and Evaluation of the Surface_mesh Data Structure". The main goal is to allow non-manifold geometry and mixed dimensional components (tets, tris, segments), while being relatively simple to manipulate. [GitHub link]
3D Liquid Simulator code A minimal grid-based 3D liquid simulator and OpenGL viewer, using semi-Lagrangian advection, volumetric particles for the liquid, ghost fluid free surface conditions, and support for irregular solid boundaries using the variational/finite-volume approach from our SIG'07 paper. The only dependencies should be the GLUT library, so it's hopefully easy to set up and experiment with. Here's a sample clip. Update: I also added another version with our variational viscosity technique implemented in 3D. [Inviscid code, on GitHub] [With viscosity, on GitHub]
2D Variational Viscosity code Sample code illustrating how to use our variational viscosity discretization to support rotation and buckling and variable viscosity within the liquid solver below. [Github link]
2D Variational Pressure Projection code Sample codes illustrating how to use our variational pressure projection to support static irregular geometry within a very simple 2D "stable fluids" style fluid solver. Air - Single phase fluid solver with static obstacles. Liquid - Free surface liquid solver with static obstacles. This code combines our irregular solid boundary discretization with the 2nd order free surface pressure boundary condition of Enright et al. 2003.
SDFGen: Signed Distance Field Generator for triangle meshes A simple command-line utility to construct a signed distance field from a triangle mesh, which is often useful for physics-based animation, such as in processing collisions for rigid objects. [Github link]
Watertight Stanford bunny I ran into some problems due to the holes in the bunny, and since I couldn't find a watertight version online, I made one myself (for non-commercial use, of course). It's also in OBJ format, rather than the original PLY. In addition to his appearances in my fluid papers, he recently played a minor supporting role in Djeu et al '09. Thanks to the Stanford 3D Scanning Repository for the original model.
2D Polygon Moment of Inertia Tensor Code I couldn't find any convenient code for computing 2D inertia tensors from the vertices and edges of a simple polygon, so I adapted/specialized Michael Kallay's excellent 3D code from the Journal of Graphics Tools article Computing the Moment of Inertia of a Solid Defined by a Triangle Mesh. The article mentions how to handle 2D bodies, but the accompanying code supports only 3D objects. My code provides the corresponding 2D implementation, while retaining the speed, brevity, and clarity of the original.
Higher Order Data Extrapolation in the Normal Direction A sample Matlab implementation of quadratic extrapolation in the normal direction of a function from a region defined by a given signed distance function into a surrounding undefined region, essentially following Ng et al. 2009, Min & Gibou 2007, and Aslam 2003. This can be useful for extrapolating known velocities from a fluid region into a solid region, such as in the Ghost Fluid Method, for example.

Background:


	My PhD is from the Computer Science Department at the University of British Columbia in Vancouver, BC. I worked under the supervision of Dr. Robert Bridson , and defended my dissertation in fall of 2010. During my degree I consulted for Ottawa-based Exocortex Technologies, and interned at Weta Digital in New Zealand, and Intel's Applications Research Lab in Santa Clara, California.

	Before pursuing a PhD, I worked at Frantic Films VFX (since bought by Prime Focus VFX), a Winnipeg-based visual effects studio where I was a Software Engineer in the Research and Development group. My job was to develop physics tools for artists based on recent academic research, including smoke, water, and rigid and deformable bodies. These tools were used on various films, including Superman Returns, Scooby-Doo 2: Monsters Unleashed, and Cursed.

	I'm a graduate of the Computer Science Honours Co-op program at the University of Manitoba, having completed my Bachelor of Computer Science degree in the fall of 2003. I also interned at OTI (original developers of Eclipse, now a subset of IBM) and Protegra, Inc.

Miscellaneous:

	Course project: Implementing Energy Redistribution Path Tracing Energy redistribution path tracing is a rendering method that hybridizes Monte Carlo path tracing with Metropolis Light Transport. I modified PBRT to support ERPT for a course project in 2005. A few people have contacted me with regards to this project, so I'm leaving the report online in case others find it useful.
	Some thoughts about the problem of reconstructing tri-meshes from signed distances.
	I wrote some quick code to tally SIGGRAPH papers by institution from 2005-2010, and posted the results here.