Center for Human Modeling and Simulation

Empirical developments in retraction

B K. Redman — Thu, 03 Sep 2009 11:24:59 PDT

This study provides current data on key questions about retraction of scientific articles. Findings confirm that the rate of retractions remains low but is increasing. The most commonly cited reason for retraction was research error or inability to reproduce results; the rate from research misconduct is an underestimate, since some retractions necessitated by research misconduct were reported as being due to inability to reproduce. Retraction by parties other than authors is increasing, especially for research misconduct. Although retractions are on average occurring sooner after publication than in the past, citation analysis shows that they are not being recognised by subsequent users of the work. Findings suggest that editors and institutional officials are taking more responsibility for correcting the scientific record but that reasons published in the retraction notice are not always reliable. More aggressive means of notification to the scientific community appear to be necessary.

Real-time Inverse Kinematics Techniques for Anthropomorphic Limbs

Deepak Tolani — Wed, 10 Dec 2008 07:09:17 PST

In this paper we develop a set of inverse kinematics algorithms suitable for an anthropomorphic arm or leg. We use a combination of analytical and numerical methods to solve generalized inverse kinematics problems including position, orientation, and aiming constraints. Our combination of analytical and numerical methods results in faster and more reliable algorithms than conventional inverse Jacobian and optimization-based techniques. Additionally, unlike conventional numerical algorithms, our methods allow the user to interactively explore all possible solutions using an intuitive set of parameters that define the redundancy of the system.

Animation Control for Real-Time Virtual Humans

Norman I. Badler — Fri, 01 Aug 2008 09:14:29 PDT

The computation speed and control methods needed to portray 3D virtual humans suitable for interactive applications have improved dramatically in recent years. Real-time virtual humans show increasingly complex features along the dimensions of appearance, function, time, autonomy, and individuality. The virtual human architecture we've been developing at the University of Pennsylvania is representative of an emerging generation of such architectures and includes low-level motor skills, a mid-level parallel automata controller, and a high-level conceptual representation for driving virtual humans through complex tasks. The architecture--called Jack-- provides a level of abstraction generic enough to encompass natural-language instruction representation as well as direct links from those instructions to animation control.

Multi-Level Shape Representation Using Global Deformations and Locally Adaptive Finite Elements

Dimitris Metaxas — Mon, 19 May 2008 08:14:04 PDT

We present a model-based method for the multi-level shape, pose estimation and abstraction of an object's surface from range data. The surface shape is estimated based on the parameters of a superquadric that is subjected to global deformations (tapering and bending) and a varying number of levels of local deformations. Local deformations are implemented using locally adaptive finite elements whose shape functions are piecewise cubic functions with C¹ continuity. The surface pose is estimated based on the model's translational and rotational degrees of freedom. The algorithm first does a coarse fit, solving for a first approximation to the translation, rotation and global deformation parameters and then does several passes of mesh refinement, by locally subdividing triangles based on the distance between the given datapoints and the model. The adaptive finite element algorithm ensures that during subdivision the desirable finite element mesh generation properties of conformity, non-degeneracy and smoothness are maintained. Each pass of the algorithm uses physics-based modeling techniques to iteratively adjust the global and local parameters of the model in response to forces that are computed from approximation errors between the model and the data. We present results demonstrating the multi-level shape representation for both sparse and dense range data.

A Machine Translation System from English to American Sign Language

Liwei Zhao — Mon, 19 May 2008 08:14:02 PDT

Research in computational linguistics, computer graphics and autonomous agents has led to the development of increasingly sophisticated communicative agents over the past few years, bringing new perspective to machine translation research. The engineering of language-based smooth, expressive, natural-looking human gestures can give us useful insights into the design principles that have evolved in natural communication between people. In this paper we prototype a machine translation system from English to American Sign Language (ASL), taking into account not only linguistic but also visual and spatial information associated with ASL signs.

Human Task Animation from Performance Models and Natural Language Input

Jeffrey Esakov — Fri, 14 Sep 2007 08:31:10 PDT

Graphical manipulation of human figures is essential for certain types of human factors analyses such as reach, clearance, fit, and view. In many situations, however, the animation of simulated people performing various tasks may be based on more complicated functions involving multiple simultaneous reaches, critical timing, resource availability, and human performance capabilities. One rather effective means for creating such a simulation is through a natural language description of the tasks to be carried out. Given an anthropometrically-sized figure and a geometric workplace environment, various simple actions such as reach, turn, and view can be effectively controlled from language commands or standard NASA checklist procedures. The commands may also be generated by external simulation tools. Task timing is determined from actual performance models, if available, such as strength models or Fitts' Law. The resulting action specifications are animated on a Silicon Graphics Iris workstation in real-time.

Terrain Navigation Skills and Reasoning

Hyeongseok Ko — Wed, 12 Sep 2007 08:46:07 PDT

We describe a real-time model of terrain traversal by simulated human agents. Agent navigation includes a variety of simulated sensors, terrain reasoning with behavioral constraints, and detailed simulation of a variety of locomotion techniques. Our Kinematic Locomotion Generation Module (KLOG) generates various terrain navigation skills as well as both rhythmic and non-rhythmic variations of these skills. The terrain navigation skills include curved path walking, lateral or backward stepping, running, and the transitions between walking and running for motion continuity. Locomotion attributes such as pelvis rotation and translation and torso flexion and twist are used to modify the KLOG skills so that realistic looking rhythmic locomotion or non-rhythmic variations, such as ducking under a low hanging branch of a tree, can be achieved. The path through the terrain is incrementally computed by a behavioral reasoning system configuring a behavioral feedback network. A number of sensors acquire information on object range, passageways, obstacles, terrain type, exposure to hostile agents and so on. The behavioral reasoner weighs this information along with collision avoidance, cost, danger minimization, locomotion types and other behaviors available to the agent and incrementally attempts to reach a goal location. Since the system is reactive, it can respond to moving obstacles, changing terrain, or unexpected events due to hostile agents or the effects of limited perception.

Efficient Re-rendering of Naturally Illuminated Environments

Jeffry S. Nimeroff — Wed, 12 Sep 2007 07:53:59 PDT

We present a method for the efficient re-rendering of a scene under a directional illuminant at an arbitrary orientation. We take advantage of the linearity of the rendering operator with respect to illumination for a fixed scene and camera geometry. Re-rendering is accomplished via linear combination of a set of pre-rendered "basis" images. The theory of steerable functions provides the machinery to derive an appropriate set of basis images. We demonstrate the technique on both simple and complex scenes illuminated by an approximation to natural skylight. We show re-rendering simulations under conditions of varying sun position and cloudiness.

Model-based Analysis of Cardiac Motion from Tagged MRI Data

Jinah Park — Wed, 12 Sep 2007 07:34:11 PDT

We develop a new method for analyzing the motion of the left ventricle (LV) of a heart from tagged MRI data. Our technique is based on the development of a new class of physics-based deformable models whose parameters are functions allowing the definition of new parameterized primitives and parameterized deformations. These parameter functions improve the accuracy of shape description through the use of a few intuitive parameters such as functional twisting. Furthermore, these parameters require no complex post-processing in order to be used by a physician. Using a physics-based approach, we convert these geometric models into deformable models that deform due to forces exerted from the datapoints and conform to the given dataset. We present experiments involving the extraction of shape and motion of the LV from MRI-SPAMM data based on a few parameter functions. Furthermore, by plotting the variations over time of the extracted model parameters from normal and abnormal heart data we are able to characterize quantitatively their differences.

A Framework for Global Illumination in Animated Environments

Jeffry S. Nimeroff — Wed, 12 Sep 2007 06:12:07 PDT

We describe a new framework for efficiently computing and storing global illumination effects for complex, animated environments. The new framework allows the rapid generation of sequences representing any arbitrary path in a "view space" within an environment in which both the viewer and objects move. The global illumination is stored as time sequences of range images at base locations that span the view space. We present algorithms for determining locations for these base images, and the time steps required to adequately capture the effects of object motion. We also present algorithms for computing the global illumination in the base images that exploit spatial and temporal coherence by considering direct and indirect illumination separately. We discuss an initial implementation using the new framework. Results from our implementation demonstrate the efficient generation of multiple tours through a complex space, and a tour of an environment in which objects move.