Tianlu Mao

Technical Section: Continuum crowd simulation in complex environments

This paper presents a novel approach for crowd simulation in complex environments. Our method is based on the continuum model proposed by Treuille et al. [13]. Compared to the original method, our solution is well-suited for complex environments. First, we present an environmental structure and a corresponding discretization scheme that helps us to organize and simulate crowds in large-scale scenarios. Second, additional discomfort zones around obstacles are auto-generated to keep a certain, psychologically plausible distance between pedestrians and obstacles, making it easier to obtain smoother trajectories when people move around these obstacles. Third, we propose a technique for density conversion; the density field is dynamically affected by each individual so that it can be adapted to different grid resolutions. The experiment results demonstrate that our hybrid solution can perform plausible crowd flow simulations in complex dynamic environments.

A semantic environment model for crowd simulation in multilayered complex environment

Simulating crowds in complex environment is fascinating and challenging, however, modeling of the environment is always neglected in the past, which is one of the essential problems in crowd simulation especially for multilayered complex environment. This paper presents a semantic model for representing the complex environment, where the semantic information is described with a three-tier framework: a geometric level, a semantic level and an application level. Each level contains different maps for different purposes and our approach greatly facilitates the interactions between individuals and virtual environment. And then a modified continuum crowd method is designed to fit the proposed virtual environment model so that realistic behaviors of large dense crowds could be simulated in multilayered complex environments such as buildings and subway stations. Finally, we implement this method and test it in two complex synthetic urban spaces. The experiment results demonstrate that the semantic environment model can provide sufficient and accurate information for crowd simulation in multilayered complex environment.

CrowdViewer: from simple script to large-scale virtual crowds

Visualization of large-scale virtual crowds is ubiquitous in many applications of computer graphics. For reasons of efficiency in modeling, animating and rendering, it is difficult to populate scenes with a large number of individually animated virtual characters in real-time applications. In this paper, we present an effective and readily usable solution to this problem. It accepts simple script which includes motion state and position information of each individual at each time step. Supported by material database and motion database, various human models are generated from model templates, and then driven by an agile on-line animation approach. A developed point-based rendering approach is presented to accelerate rendering. We test our system with script including 30,000 people evacuating from a sports arena. The results demonstrate that our approach provides a very effective way to visualize large-scale crowds with high visual realism in real-time.

Parallelizing continuum crowds

In this paper, we present a novel parallelizing method for crowd simulators constructed with a continuum model rather than an agent-based model. The basic idea is to partition a crowded virtual environment into some districts, each of which keeps its own dynamic continuum fields and has several transitional blocks to make individuals keep continuum motion from one district to another. Our method makes continuum models to be parallelizable while preserving their existing superiority of generating smooth motion. Moreover, for most of large-scale applications, our partitioning method effectively simplifies the complexity of simulation. Experiments show that our method has achieved super-linear speedup and could employ more than one hundred worker processors to simulate 1 million people in an area of 672,400m2.

An efficient lane model for complex traffic simulation

Traffic simulation heavily relies on lane model. This paper presents a novel method to model lanes based on the road axis under the Frenet frame. The road axis is generated from the geographic information system data after curve approximation, discretization, and compression. This lane model couples mileage information with three‐dimensional geometric information, so it offers an easy and fast position transformation from mileage to the Cartesian coordinate. It also keeps strictly consistent for mileage among neighboring lanes so that it facilitates lane‐change processing. Compared with existing methods that depict lanes as simple polylines or curves, the proposed lane model is more functional and more efficient, especially for complex traffic simulation with a large number of lane‐changes. Copyright

Automatic joints extraction of scanned human body

This paper presents an automatic method to extract joints accurately from scanned human body shape. Firstly, model is divided into slices by a group of horizontal parallel planes and primary landmarks are determinated according to the slices. Additionally, we propose a model intersection method based on direction of limbs. Model is separated into five segments including torso and four limbs and approximate direction of each segment can be calculated according to the primary landmarks. Five groups of parallel planes perpendicular to corresponding segments are employed to divide each segment into slices, and contours are calculated by intersection detection between planes and triangles. Finally, we propose a circularity function differentiation technique to extract key contours at joints from segments and the joints can be calculated according to centroids of the key contours. The experimental results demonstrate that the method has more advantages than the conventional ones, especially in algorithms accuracy and robustness.

An all-in-one efficient lane-changing model for virtual traffic

Modeling lane changes realistically play an important role in traffic animations. Existing models for traffic simulations mostly focus on lane‐changing decision‐making. They cannot describe how lane‐changing processes go on. Though some methods in motion planning can be further used to describe the processes, they are time‐consuming. In this paper, we present an all‐in‐one model for lane‐changing animations. We transform all conditions for lane‐changing decision‐making into constraints on lane‐changing trajectories. We use two polynomials designed in moving reference frames to describe the trajectories. The whole lane‐changing process, whether it can occur and how it goes on, is determined by whether there is a valid trajectory. It only takes O(1) time for the determination. Experiment results show that our model can describe lane‐changing processes realistically and efficiently. Copyright

Evoking panic in crowd simulation

In order to exhibit panic phenomenon in the crowd simulation, special rules or parameters setting is needed for a given scene. In this paper, we present a panic model, named PPIB (Panic, Propagation and Influence on Behavior), which could evoke panic automatically under dangerous situation without manual intervention. PPIB describes panic behavior in three perspectives, including human mental factors and their variation caused by local situation, panic propagation, and influence of panic over the basic factors of pedestrian dynamic. Experiments show that combined with a dynamical crowd model, PPIB could evoke a wide variety of panic behaviors and exhibit emergent phenomena in crowd simulation.

Evaluating simplified air force models for cloth simulation

Any cloth simulation system needs the aerodynamics model to describe the dynamic behavior of the cloth interacting with the air. Different air force model has different simplification treatment with different approximation degree. In this paper, we present a quantitative evaluation method for simplified air force models, and experimentally investigate 5 different air force models which are all commonly used in cloth simulations. The results show that the lift component, which was usually neglected in air force models, actually plays an important role in the simulation. Moreover, when the air field is simplified as the linear global wind field, the air force model containing the linear drag component and simple upward lift component matches the real cloth motion better than the complicated nonlinear ones.

A faster method for modeling virtual colony

A virtual colony composed by vivid personal characters with different facial texture and body size, will strongly enhance the reality of the whole virtual environment. This paper describes a fast, economic but realistic method for modeling virtual colony. The system has two major components: photographs based human model reconstruction and anthropometry based automatic human model edit, both of them were advanced to achieve more practical and realistic purpose. To demonstrate the power of this approach, the method was applied to generate some virtual colonies.