Social Forces Model with Human participants on the BBC

The BBC's science series 'Bang goes the Theory' recently had an episode on crowd behaviour. It shows a fascinating way of getting plenty of research out there into the public eye, using very short clips of research taking place based on certain themes. Anders Johansson, who still works with CASA, ran an experiment based on the 'social forces' model.

To give a heads up, the social forces model is an agent based model that simulates the microscopic movements of pedestrians. The motion of these pedestrians are described by subjecting them to 'social forces'. These forces are exerted by the pedestrians personal environment, as well as the interactions with other pedestrians in this context.

The movement of these pedestrians governed by these social forces are defined by the equation below:



If you'd like more details on the paper, it can be found here

An example of a social forces simulation model can be seen running in this video below:




Now, with this BBC episode, you can check out this model in a real world example with the help of an experiment with human participants, where you can see the effect of jams during an evacuation in a potential real world situation, and how a very simple solution of placing an obstacle at the exit can actually improve the flow of people through a door when evacuating a building. Although, your intuition I'm sure would say that it would not make sense. Actually, as this obstacle separates the flow of people, it prevents a jam occuring at the door, and therefore, creates a smoother flow through the door. Have a look, it's available for another 10days, and the experiment runs from around the 24 min mark, UK users only I'm afraid:

BBC Bang goes the Theory S6 Ep 4

Enjoy!

Simulation of Starlings flocking behaviour using captured 3D video recordings of Starlings in flight

I was quite interested to find this flocking simulation of starling's on MIT's Physics arXiv blog.

I mentioned Reynold's flocking behaviour model in an earlier post, it's nice to see progress has been made in creating more accurate simulations by actually capturing 3D recordings using stereographic photography of real starlings in flight.



These video recordings that were published last year has actually allowed Charlotte Hemelrijk at the University of Groningen to create a flocking model, and vary the parameters that closely match real flight recordings of the starlings.

These birds have very complex rules creating this self-organising behaviour, and the researchers seem to have been able to take apart the rules that govern them. These rules also govern other species such as fish, insects and even human crowds, and will likely give further insight into crowd behaviour, and allow for more accurate simulations of human crowds.

I'll be looking forward to seeing a video of this flocking simulation.

Big, Fast Crowds on the Sony PlayStation 3

Craig Reynolds first introduced flocking to the computer graphics area by creating the Boids artificial life simulation in 1986. It was a computer model of coordinated animal motion such as bird flocks or fish schools, that allowed for collision avoidance and goal seeking. This model has had various applications such as bat swarms and penguin flocks in the movie 'Batman Returns'. A video of the early model can be seen below, further details can be found here


The above model has a complexity of O(n²), as each boid needs to consider each other boid in order to determine whether its a nearby flockmate. The complexity can be reduced to O(n), by the use of spatial hashing that keeps the boids sorted according to their location, and therefore, increase the population of the boids.

Craig now works for the US R&D group of Sony Computer Entertainment. Recently he created a crowd simulation on the Sony PlayStation 3, which extends from the very early model above. As spatial hashing is used in order to accomodate large numbers of agents, here, it forms the basis of a scalable multi-processor approach to create large, fast crowd simulations. The PlayStation 3 has Cell processor, which consists of a Power Processor Unit (PPU), multiple Synergistic Processor Units (SPU) - 6 available to the model, and an RSX GPU. The model makes use of this architecture to spatially subdivide regions, and use the multiple SPUs to update a number of regions in parallel, accelerating the crowd simulation. The model has been able to incorporate 15,000 agents running at 60fps. A video can be seen by clicking the picture below:


It is interesting to see how different architectures can be used to create crowd simulations, and how the parallel processing nature of today's video games consoles, make them low-cost and high performance platforms for parallel execution. I will be looking forward to see other general purpose applications of the Sony PS3.