Computer Science
Program  Emeritus
Address:

Traditional Courses of Mine:
B581, Graduate Computer Graphics, taught about 30 times.
Public B581 syllabus: Overview of B581.
This is an OpenGLbased course introducing the mathematical foundations and practical programming methods of modern interactive computer graphics. The homework involves coding in C using OpenGL and GLUT, and mastering the theoretical principles upon which OpenGLlike graphics is based. The course emphasizes creating interactive interfaces to help understand the graphics objects and techniques being studied. Lighting and simple material modeling are covered as an introduction to the creation of realistic images.
B689, Mathematical Modeling Methods, taught half a dozen times
Public B689 syllabus: Overview of B689.This course focused on Mathematicabased methods of producing rapid prototypes solving complex software modeling problems. This class will start with an introduction to the Mathematica programming environment, and will incorporate Mathematica prototyping methods implicitly into a broad survey of mathematical modeling methods, techniques, and folklore used widely throughout computer science, computer graphics, scientific visualization, mathematics, and physics.

Click here for a larger version 
4Dice is (free) iPhone App.
See our
IEEE COMPUTER paper on the design of 4Dice,
IEEE Computer, Volume 45, Number 9, pp.8088 (September,
2012).
Alternative site for PDF:
see also here.
4Dice is an interactive application using our 4D Rolling Ball algorithm combined with the graphically correct 4D backfaceculled representation of the hypercube introduced in the 4Dice video animation (see below). This is a collaborative project with Xiaoqi Yan and Prof. Philip ChiWing Fu at NTU, Singapore. The 4Dice oneminute YouTube video provides a quick introduction to the issues of properly visualizing a backface culled hypercube; the 4Dice iPhone App provides interactive exploration of all the concepts introduced in the animation. 




 
The images you see in the 4Dice interactive application
actually form a wireframe torus when you turn off backface
culling. The deep reason for this is that the hypercube is a simple
tessellation of a 3sphere (which has Euler characteristic zero)
surrounding a 4ball, and a nice parameterization of the 3sphere
involves a nested family of tori; the wireframe hypercube is
effectively a rectangular tessellation of the "center"
member of this family of tori. It is known that such a set of
edges, with four edges meeting at each vertex, admits
an Eulerian
path. The figure on the left shows one of many such paths
that can be constructed, with a ratio of 
Selected Publications of Interest
Visualizing Quaternions
(MorganKaufmann/Elsevier, 2006, ISBN 9780120884001)
is a comprehensive approach to the
significance and applications of quaternions,
and focuses on the exploitation of Quaternion Fields,
a tool developed primarily by the author.
The official website for the book is maintained by the publisher, and provides background material, downloadable material from tables, and demonstration software. I maintain a local companion website here, which may be more up to date. Updates and Errata are maintained on the update
and errata page.
An example is the closed form doublereflection quaternion form
 

Winner with coauthor Sidharth Thakur of the
2012 JMGM Graphics Prize.
See also the
MGMS/Elsevier Graphics Award. Quaternion maps of protein amino acid residues provide an alternative to Ramachandran plots for orientation analysis. Several alternative orientation frame systems can be chosen, with the residuelocal C_{α}centered frame being the default. Quaternion maps are noteworthy for their ability to compare the orientations of arbitrary sets of sequential or nonsequential residues located anywhere on the protein, and for the resulting opportunity to observe and analyze the statistical properties of global orientation clusters. Only the quaternion representation of orientation frames embodies a natural rigorous measure for comparing properties of sets of global orientation frames.  
Quaternion Applications were covered in our updated quaternion tutorial lectures presented at Siggraph Asia 2012, 29 November in Singapore. Special application topics included optimal, smoothly controllable tubing and tube texturing, quaternion protein maps, and how dual quaternions solve the conundrum of how a quaternion acts on a vector. The latter is a longstanding controversy that pitted Hamilton against many contemporaries, and has been described in wondrous detail by Altmann in "Hamilton, Rodrigues, and the Quaternion Scandal."; The solution is simply to replace Hamilton's impossible candidate for
a "Vector," the binary rotation quaternion Visualizing Relativity using complexified quaternions was part of the material covered by Andrew Hanson and Daniel Weiskopf in their Siggraph 2001 Course 15 Notes. The Solar Journey DVD contains an educational computer animated film on the astronomy of the local neighborhood of the Earth and the Sun developed as part of our NASAsponsored research work. The DVD version containing the Solar Journey animation and supplementary science materials is distributed by FinleyHoliday Films. 
Some day I'll put together an annotated bibliography, but for now see the Google Scholar and DBLP project links at the top of the web page. Here is a summary of my historically most highly cited work, and together with some media links.
The EguchiHanson metric (Physics Letters 74B, pp. 249251 (1978)) is a vacuum solution of the Euclidean Einstein equations that is the first known instance of an important class of metrics now commonly referred to as ALE or Asymptotically Locally Euclidean metrics. A comprehensive review of Euclidean Einstein metrics and the context of the EguchiHanson metric is given in our 1979 Annals of Physics review article. This work won the Second Prize in the 1979 Gravity Research Foundation Competition; see T. Eguchi and A.J.Hanson, "Gravitational Instantons," Journal of General Relativity and Gravitation, 11, pp. 315320 (1979).
Our comprehensive introduction to the ways in which the languages of the theoretical physics and mathematics communities became inseparably connected after a long history of going their separate ways is available in the 1980 Physics Reports article "Gravitation, Gauge Theories and Differential Geometry" by Eguchi, Gilkey, and Hanson.
Constrained Hamiltonian Systems, is a short book by Hanson, Regge,
and Teitelboim, originally published in 1976 by the Accademia
Nazionale dei Lincei (Contributi del Centro Linceo Interdisc. di
Scienze Matem. e loro Applic., No.22, Accademia Nazionale dei Lincei,
Rome, 135 pages (1976)). Actual print copies of this work are rare
and generally unavailable.
Media. The fourdimensional MeshView viewer is described in the Meshview tech note, and downloadable software is located HERE. Supported fully under Xwindows/Motif only. Precompiled for Linux, Macintosh, SUN SOLARIS, and SGI IRIX. Recently available: reduced functionality Windows XP version. The shortcuts work in the Windows version, but you need to look at the Linux version to see what they are.
Research
My most recent research focuses on several areas: Mathematical Visualization, Virtual Reality, and Astronomy.
A Tessellation for Fermat Surfaces in CP^{3},
DOI link
10.1016/j.jsc.2008.09.002, appears in the Journal of Symbolic Computation
(Sept 2008). This work presents an explicit algorithm for tessellating
the algebraic surfaces (real 4manifolds) F(n) embedded in
CP^{3} defined
by the "Fermat" equation
 
Dual FivePoint Function Geometry.
This work investigates the geometry of twocomplexvariable
contour integration using the classic 1960's Dual 5Point Function of
the early string model as the critical example. The investigation
actually began with some questions introduced in a very early
paper, Dual NPoint Functions in
PGL(N2,C)Invariant Formalism (A. J. Hanson, Physical Review, 1972).
A number of new insights are given in our paper "A Contour Integral Representation for the Dual FivePoint Function and a Symmetry of the Genus Four Surface in R6" by Andrew J. Hanson and JiPing Sha, DOI link 10.1088/03054470/39/10/01, which is published in J. Phys. A: Mathematics and General., vol. 39, pages 25092537 (2006). There is also a version on the arXiv, mathph/0510064. A local copy can be found here. 
Other topics. Various longterm projects deal with techniques for modeling, depicting, and interacting with geometric structures of extreme complexity. Subject domains of interest range from mathematical objects in four dimensions to exploiting quaternions to represent orientation fields of geometric objects. Recent work concerns rephrasing some of the classical differential geometry of curves and surfaces directly in terms of quaternion fields; an application is the determination of optimal framings of curves and surfaces by minimizing appropriate energies of the quaternion frame fields ("quaternion Gauss maps") in the 3sphere.
An example of our work on star rendering embedded in the Solar Journey package may be found in this QuickTime movie depicting simulated stars, which compares favorably to real images such as Akira Fujii's Orion.
Selected papers of ours in this area:
Visualizing Multiwavelength Astrophysical Data, Hongwei Li, ChiWing Fu, and Andrew J. Hanson, TVCG, Nov/Dec 2008, 14, no. 6, pp. 15551562, Proceedings of IEEE Visualization 2008. Describes a unique interactive GPUdriven volumerendering paradigm tailored to the study of allsky multispectral astrophysical data. Paper web site. 
Visualizing LargeScale Uncertainty in Astrophysical Data, Hongwei Li, ChiWing Fu, Yinggang Li, and Andrew J. Hanson, TVCG, Nov/Dec 2007, 13, no. 6, pp. 15401647; Proceedings of IEEE Visualization 2007. Astrophysical data is characterized by a wide variety of uncertainties and error sources; this work provides a set of tools for examining and visualizing these features. Paper and web site. 
A Transparently Scalable Visualization Architecture for Exploring the Universe, TVCG, Jan/Feb 2007, is a full description of work done mainly by ChiWing Fu in my laboratory. This framework supports transparent interactive navigation across enormous scale ranges such as those naturally occurring in astronomy. Paper and web site. 
Scalable WIM: Effective Exploration in Largescale Astrophysical Environments, TVCG, Sept/Oct 2006, 12, pp. 10051011; Proceedings of IEEE Visualization 2006. Describes a WorldinMiniature interface design for astrophysical exploration whose development was led by Yinggang Li in my laboratory. Paper and web site. 
The Sun's interaction with its environment. This image of the heliosphere, representing the interaction of the Solar wind with the surrounding interstellar material, is taken from our short film "Solar Journey;" an extended version of the film will be produced for public distribution on videotape and DVD during the coming year. The shapes depicted here utilize a theoretical model by Timur Linde from the University of Chicago. The image has appeared as the Astronomy Picture of the Day, APOD 2002 June 24, and was used as an illustration in a recent astronomy news article in Science Magazine, page 2005 of Vol. 300, 27 June 2003. (The image credit is very obscure, in tiny verticallyaligned print along the spine of page 2005.) 
Satellites in our Sky (GMT June 24th 2003 2:21pm). We have over a thousand satellites flying through the sky over our heads. This image is from a brief animation representing a user's interaction with our Earthday graphics program. The animation shows a large portion of these at a selected time, and then zooms in for a closeup of the International Space station (ISS). We can clearly see the ring structure of geostationary (deepspace) satellites rotating with the Earth, located 38,500km above the Earth's surface (about 6 times the radius of the Earth). The entire animation appeared as the Astronomy Picture of the Day on 14 July 2003. See APOD 2003 July 14. 
Our initial work on handling very large scales of spacetime
in interactive virtual reality environments is described in our paper, Very large
scale visualization methods for astrophysical data, which appears in
Proceedings of Joint EurographicsIEEE TVCG Symposium on Visualization,
May 2931, 2000, Amsterdam, the Netherlands. This paper is part of the
published proceedings, © SpringerVerlag.
Our most extensive recent work, which appeared in TVCG in January 2007, describes the maturation of the scaling framework developed in Philip ChiWing Fu's PhD thesis, and is entitled "A Transparently Scalable Visualization Architecture for Exploring the Universe." For details, see the summary web site.
I have also created a variety of graphics images derived from the Fermat Equation (see below) that are relevant to the CalabiYau spaces that may lie at the smallest scales of the unseen dimensions in String Theory; these have appeared in Brian Greene's books, The Elegant Universe and The Fabric of the Cosmos,, and in the book by Callender and Huggins, Physics Meets Philosophy at the Planck Scale. The writhing purple shapes in the October/ November 2003 NOVA production Elegant Universe, as well as the cover of the November 2003 Scientific American, were derived from software models I supplied to the NOVA graphics providers.
These images show equivalent renderings of a 2D crosssection of the
6D manifold embedded in CP4 described in string theory calculations by the
homogeneous equation in five complex variables:
z_{0}^{5} + z_{1}^{5} +
z_{2}^{5} + z_{3}^{5} +
z_{4}^{5} = 0
The surface is computed by assuming that some pair of complex inhomogenous
variables, say z_{3}/z_{0} and z_{4}/z_{0}, are constant (thus defining
a 2manifold slice of the 6manifold), normalizing the resulting inhomogeneous
equations a second time, and plotting the solutions to
z_{1}^{5} + z_{2}^{5} = 1
The resulting surface is embedded in 4D and projected to 3D using Mathematica
(left image) and our own interactive MeshView 4D viewer (right image). If
you have
CosmoPlayer, you can also
interact with this VRML version
of the quintic CalabiYau crosssection.
In the righthand image, each point on the surface where five differentcolored patches come together is a fixed point of a complex phase transformation; the colors are weighted by the amount of the phase displacement in z1 (red) and in z2 (green) from the fundamental domain, which is drawn in blue and is partially visible in the background. Thus the fact that there are five regions fanning out from each fixed point clearly emphasizes the quintic nature of this surface.
For further information, see: A.J. Hanson. A construction for computer visualization of certain complex curves. Notices of the Amer. Math. Soc., 41(9):11561163, November/December 1994.
An interactive version is available at
the Wolfram Demonstrations Project CalabiYau
Space page, based on the Hanson paper cited above, with
assistance from Jeff Bryant.
Arbitrary Genus Surfaces:
This image shows my computer graphics construction of a fourhole
torus described by an equation in complex twospace given by H. Blaine
Lawson, "Complete Minimal Surfaces in S^{3}," Ann. of Math. 92,
pp.~335374 (1970), with m = n = 2,
Im z1^{(m + 1)} + z2^{(mn)} Im z2^{(n+1)}
= 0
and
z1^{2} + z2^{2} = 1
In general,
the genus is m*n, and this surface is not actually minimal in S^{3}
except for
m = n = 0 and m = n = 1.
Review article
Cover picture: IEEE Computer 27 (July 1994)
Mathematics and Physics Animations
We have produced a number of short video animations with mathematical and physical content. Some of my favorite projects are the following: