Artists, animation and game designers are in demand for solutions to easily populate large virtual environments with crowds that satisfy desired visual features. This paper presents a method to intuitively populate virtual environments by specifying two key features: localized density, being the amount of agents per unit of surface, and localized flow, being the direction in which agents move through a unit of surface. The technique we propose is also time-independant, meaning that whatever the time in the animation, the resulting crowd satisfies both features.

To achieve this, our approach relies on the Crowd Patches model. After discretizing the environment into regular patches and creating a graph that links these patches, an iterative optimization process computes the local changes to apply on each patch (increasing/reducing the number of agents in each patch, updating the directions of agents in the patch) in order to satisfy overall density and flow constraints. A specific stage is then introduced after each iteration to avoid the creation of local loops by using a global pathfinding process.

As a result, the method has the capacity of generating large realistic crowds in minutes that endlessly satisfy both user specified densities and flow directions, and is robust to contradictory inputs. At last, to ease the design the method is implemented in an artist-driven tool through a painting interface.

We introduce "Crowd Sculpting": a method to interactively design populated environments by using intuitive deformation gestures to drive both the spatial coverage and the temporal sequencing of a crowd motion.

Our approach assembles large environments from sets of spatial elements which contain inter-connectible, periodic crowd animations. Such a "Crowd Patches" approach allows us to avoid expensive and difficult-to-control simulations. It also overcomes the limitations of motion editing, that would result into animations delimited in space and time.

Our novel methods allows the user to control the crowd patches layout in ways inspired by elastic shape sculpting: the user creates and tunes the desired populated environment through stretching, ending, cutting and merging gestures, applied either in space or time.

Our examples demonstrate that our method allows the space-time editing of very large populations and results into endless animation, while offering real-time, intuitive control and maintaining animation quality.

We present a novel algorithm for populating and animating an environment of a given density. Our algorithm considers two kind of densities: static density (when people doesn’t move) and dynamic density (when people move). The resulting flows of characters are computed according to a density map provided by a user. We discuss the advantages and drawbacks of the proposed solution, as well as future work.

For many applications, exploring empty virtual cities is not sufficient: streets and squares need to be populated by crowds of virtual humans. This position paper addresses the problem of generating such crowds when the scale of the city prevents the use of standard simulation methods. We first present the concept of crowd patches and review their advantages and drawbacks for animating large crowds of people. We then discuss the goals of our future work, namely being able to interactively design such large populations.