Extreme-Density Crowd Simulation: Combining Agents with Smoothed Particle Hydrodynamics

Abstract

In highly dense crowds of humans, collisions between people occur often. It is common to simulate such a crowd as one fluid-like entity (macroscopic), and not as a set of individuals (microscopic, agentbased). Agent-based simulations are preferred for lower densities because they preserve the properties of individual people. However, their collision handling is too simplistic for extreme-density crowds. Therefore, neither paradigm is ideal for all possible densities. In this paper, we combine agent-based crowd simulation with the concept of Smoothed Particle Hydrodynamics (SPH), a particlebased method that is popular for fluid simulation. Our combination augments the usual agent-collision handling with fluid dynamics when the crowd density is sufficiently high. A novel component of our method is a dynamic rest density per agent, which intuitively controls the crowd density that an agent is willing to accept. Experiments show that SPH improves agent-based simulation in several ways: better stability at high densities, more intuitive control over the crowd density, and easier replication of wave-propagation effects. Our implementation can simulate tens of thousands of agents in real-time. As such, this work successfully prepares the agent-based paradigm for crowd simulation at all densities.

SPH crowds: Agent-based crowd simulation up to extreme densities using fluid dynamics

“…This paper is an extension of a conference publication [4] that presented the SPH-enhanced crowd simulation and several results. Next to an improved organization, this extended version contains the following new content:…”

“…One difficulty of SPH lies in how to treat obstacles, so that particles near obstacles perceive a meaningful density. A common solution, which we used in our previous work as well [4], is to place 'boundary particles' at regularly sampled positions inside obstacles. In each simulation frame, these boundary particles compute the SPH density and pressure just like other particles, but they do not move.…”

“…Compared to the original version of this model [10], which we also used in our previous work [4], we now use the relative velocity v i j rather than the absolute velocity v j . This adjustment greatly improves the behavior of agents.…”

“…Our preceding conference publication [4] also included a profile that used only goal reaching, so neither collision avoidance nor SPH. We will omit this profile now, as it would never be useful for any scenario where agents actively navigate towards a goal.…”

Dynamic Combination of Crowd Steering Policies Based on Context

“…Some authors have even proposed strategies to profit from two steering strategies. For instance, van Toll et al [vTBSP20] combine agent-based (the Social Forces model) and particle-based approaches (Smoothed Hydrodynamic Particles) through abstraction layers in order to improve the behaviour in high density scenarios.…”