Steering Contexts for Autonomous Agents Using Synthetic Data

Data-driven techniques have become synonymous with replication of real-world phenomena. Efforts have been underway to use these techniques in crowd simulation through a mapping of pedestrian trajectories onto virtual agents using a similarity of circumstance. These works have exposed two fundamental issues with data-driven crowds. First, robust real-world data is logistically difficult to accurately collect and filled with unknown variables, such as a person\u27s mental state, which change behavior without providing a means to replicate their effects. Second, current data-driven approaches store and search the entire set of training data to decide the next course of action for each agent. A straightforward single-model system would alleviate the burden of storing and searching the data. The problem with a monolithic model, though, is that a single steering policy cannot handle all possible scenarios. To counter this we propose the splitting of possible scenarios into separable contexts, with each context in turn learning a model. The model used by an agent can then be dynamically swapped at runtime based on the evolving conditions around the agent. This results in a more scalable approach to data-driven simulation. In lieu of tracked data from real pedestrians, we propose the use of an oracle steering algorithm. This algorithm stands in for real data and can be queried for a steering decision for any combination of factors. This allows us to more thoroughly explore the problem space as needed. Furthermore, we can control all variables and capture behavior from scenarios that are otherwise infeasible to adequately sample in reality. This synthetic source of training data allows for a scalable and structured approach to training machine-learned models which virtual agents can use to navigate at runtime

Generating a Multipliciy of Policies for Agent Steering in Crowd Simulation

Pedestrian steering algorithms range from completely procedural to entirely data-driven, but the former grossly generalize across possible human behaviors and suffer computationally, whereas the latter are limited by the burden of ever-increasing data samples. Our approach seeks the balanced middle ground by deriving a collection of machine-learned policies based on the behavior of a procedural steering algorithm through the decomposition of the space of possible steering scenarios into steering contexts. The resulting algorithm scales well in the number of contexts, the use of new data sets to create new policies, and in the number of controlled agents as the policies become a simple evaluation of the rules asserted by the machine-learning process. We also explore the use of synthetic data from an “oracle algorithm” that serves as an as-needed source of samples, which can be stochastically polled for effective coverage. We observe that our approach produces pedestrian steering similar to that of the oracle steering algorithm, but with a significant performance boost. Runtime was reduced from hours under the oracle algorithm with 10 agents to on the order of 10 frames per second (FPS) with 3000 agents. We also analyze the nature of collisions in such a framework with no explicit collision avoidance

Dynamic Search on the GPU

Path finding is a fundamental, yet computationally expensive problem in robotics navigation. Often times, it is necessary to sacrifice optimality to find a feasible plan given a time constraint due to the search complexity. Dynamic environments may further invalidate current computed plans, requiring an efficient planning strategy that can repair existing solutions. This paper presents a massively parallelized wavefront-based approach to path planning, running on the GPU, that can efficiently repair plans to accommodate world changes and agent movement, without having to restart the wavefront propagation process. In addition, we introduce a termination condition which ensures the minimum number of GPU iterations while maintaining strict optimality constraints on search graphs with non-uniform costs

Pedestrian Anomaly Detection Using Context-Sensitive Crowd Simulation

Detecting anomalies in crowd movement is an area of considerable interest for surveillance and security applications. The question we address is: What constitutes an anomalous steering choice for an individual in the group? Deviation from “normal” behavior may be defined as a subject making a steering decision the observer would not, provided the same circumstances. Since the number of possible spatial and movement configurations is huge and human steering behavior is adaptive in nature, we adopt a context-sensitive approach to assess individuals rather than assume population-wide homogeneity. When presented with spatial trajectories from processed surveillance data, our system creates a shadow simulation. The simulation then establishes the current, local context for each agent and computes a predicted steering behavior against which the person’s actual motion can be statistically compared. We demonstrate the efficacy of our technique with preliminary results using real-world tracking data from the Edinburgh Pedestrian Dataset

Caspase activation, inhibition, and reactivation: A mechanistic view

Caspases, a unique family of cysteine proteases, execute programmed cell death (apoptosis). Caspases exist as inactive zymogens in cells and undergo a cascade of catalytic activation at the onset of apoptosis. The activated caspases are subject to inhibition by the inhibitor-of-apoptosis (IAP) family of proteins. This inhibition can be effectively removed by diverse proteins that share an IAP-binding tetrapeptide motif. Recent structural and biochemical studies have revealed the underlying molecular mechanisms for these processes in mammals and in Drosophila. This paper reviews these latest advances