Andreas Panayiotou

Over the past two decades, researchers have made significant steps in simulating agent-based human crowds, yet most efforts remain focused on low-level tasks such as collision avoidance, path following, and flocking. Realistic simulations, however, require modeling high-level behaviors that emerge from agents interacting with each other and with their environment over time. We introduce Generative Crowds (Gen-C), a generative framework that produces crowd scenarios capturing agent-agent and agent-environment interactions, shaping coherent high-level crowd plans. To avoid the labor-intensive process of collecting and annotating real crowd video data, we leverage large language models (LLMs) to bootstrap synthetic datasets of crowd scenarios. We propose a time-expanded graph representation, encoding actions, interactions, and spatial context. Gen-C employs a dual Variational Graph Autoencoder (VGAE) architecture that jointly learns connectivity patterns and node features conditioned on textual and structural signals, overcoming the limitations of direct LLM generation to enable scalable, environment-aware multi-agent crowd simulations. We demonstrate the effectiveness of Gen-C on scenarios with diverse behaviors such as a University Campus and a Train Station, showing that it generates heterogeneous crowds, coherent interactions, and high-level decision-making patterns consistent with real-world crowd dynamics.

The level of realism in virtual crowds is strongly affected by the presence of diverse crowd behaviors. In real life, we can observe various scenarios, ranging from pedestrians moving on a shopping street, people talking in static groups, or wandering around in a public park. Most of the existing systems optimize for specific behaviors such as goal-seeking and collision avoidance, neglecting to consider other complex behaviors that are usually challenging to capture or define. Departing from the conventional use of Supervised Learning, which requires vast amounts of labeled data and often lacks controllability, we introduce Crowds using Example-driven Deep Reinforcement Learning (CEDRL), a framework that simultaneously leverages multiple crowd datasets to model a broad spectrum of human behaviors. This approach enables agents to adaptively learn and exhibit diverse behaviors, enhancing their ability to generalize decisions across unseen states. The model can be applied to populate novel virtual environments while providing real-time controllability over the agents’ behaviors. We achieve this through the design of a reward function aligned with real-world observations and by employing curriculum learning that gradually diminishes the agents’ observation space. A complexity characterization metric defines each agent’s high-level crowd behavior, linking it to the agent’s state and serving as an input to the policy network. Additionally, a parametric reward function, influenced by the type of crowd task, facilitates the learning of a diverse and abstract behavior “skill” set. We evaluate our model on both training and unseen real-world data, comparing against other simulators, showing its ability to generalize across scenarios and accurately reflect the observed complexity of behaviors. We also examine our system’s controllability by adjusting the complexity weight discovering that higher values lead to more complex behaviors such as wandering, static interactions, and group dynamics like joining or leaving. Finally, we demonstrate our model’s capabilities in novel synthetic scenarios.

Simulating believable crowds for applications like movies or games is challenging due to the many components that comprise a realistic outcome. Users typically need to manually tune a large number of simulation parameters until they reach the desired results. We introduce MPACT, a framework that leverages image-based encoding to convert unlabelled crowd data into meaningful and controllable parameters for crowd generation. In essence, we train a parameter prediction network on a diverse set of synthetic data, which includes pairs of images and corresponding crowd profiles. The learned parameter space enables: (a) implicit crowd authoring and control, allowing users to define desired crowd scenarios using real-world trajectory data, and (b) crowd analysis, facilitating the identification of crowd behaviours in the input and the classification of unseen scenarios through operations within the latent space. We quantitatively and qualitatively evaluate our framework, comparing it against real-world data and selected baselines, while also conducting user studies with expert and novice users. Our experiments show that the generated crowds score high in terms of simulation believability, plausibility, and crowd behaviour faithfulness.