Agent Street

Agent Street: An Environment for Exploring Agent-Based Models in Second Life


Contents:
  1. Introduction
  2. Conway's Game of Life
  3. Schelling's Segregation Model
  4. Pedestrian Evacuation Model
  5. Download the paper

Introduction
This micro-site contains information pertaining to the development of three agent based models in Second Life and complements the paper "Agent Street: An Environment for Exploring Agent-Based Models in Second Life". We describe the inner workings of the models along with providing the Linden Script code listings so that readers can recreate the models themselves. Movies on each page show the models running and demonstrate Second Life's potential for outreach and communication of agent-based models.

The original page can be found here: http://www.casa.ucl.ac.uk/abm/secondlife/

Below are two movies to give an overview of Agent Street


Agent-Street Vending Machines



Overview Movie of Agent-Street



Conway's Game of Life

Introduction:

This model is a recreation of Conway's very well known Game of Life where cells in a square grid live or die depending on the number of neighbors they have. Wikipedia has a page detailing the model here. This is the most basic of the three models and we used this to look at the suitability of Second Life as a platform for developing agent based models.

As with all the models we have tried to visualize as much of the inner workings of the model as possible so the "thinking" and "acting" states have different colors and the number of neighbors each cell has is displayed above it so that users can get an insight into how the model works.

Example Run Movie:
  • The movie below shows the model running:




Game of Life movie


Technical Details:

A PDF document containing details about how the model was implemented is available to download:
Source Code:

The Linden Scripts for this model are covered by the GNU GENERAL PUBLIC LICENSE and are available to download below:
If you prefer to get up and running more quickly we have a vending machine on Nature island that will give you a complete working copy of the model when you click on it. The SLURL below will take you straight there (this is now depreciated):

Extending the Model:

A three-dimensional version of the game of life is possible using these blocks if you stack layers of them, though it obviously behaves differently and you may need to change the neighbor thresholds that decide when a block lives or dies.


Schelling's Segregation Model

Introduction:

The second model we looked at was Thomas Schelling's model of urban segregation. Schelling originally demonstrated the concept with coins on a chess board. We have transferred the ideas into Second Life and instead use colored spheres inside a grid of houses.

Our segregation model grid


The spheres take it in turns to move. They glow to indicate who is thinking and if unhappy they float above the board and then choose a new house. A happy agent is large and an unhappy agent is small.

Graph:

In an attempt to validate the model we provide a graph in Second Life that shows the number of happy agents of each type after each iteration of the model.


Graph showing number of happy blue and red agents at each iteration


Example Run Movie:
  • The movie below shows one complete run of the model and demonstrates how segregation emerges:




Technical Details:

A PDF document containing details about how the model was implemented is available to download:
Source Code:

The Linden Scripts for this model are covered by the GNU GENERAL PUBLIC LICENSE and are available to download below:

If you prefer to get up and running more quickly we have a vending machine on nature island here that will give you a complete working copy of the model when you click on it (this is now depreciated).


Pedestrian Evacuation Model

Introduction:

The last model we developed in Second Life was a pedestrian evacuation model. This is a much more accurate simulation of real life than the previous two models and the rules that govern the agents are a lot more complicated.

The model was designed and developed by Joel Dearden based on ideas from Andrew Crooks and Andrew Hudson-Smith.


Basic Concept Model:

We started out by building a much simpler model to investigate how pedestrian behaviour could be simulated in Second Life. The agents in this model represent people wandering around a room and this forms the idea for the initial part of the final model where pedestrians wander around a room until the fire alarm goes off.

Wandering Agents Model




Movie of wandering agents


Evacuation Model Detail:

The final version of the model simulates a pedestrian evacuation in response to a fire alarm, from the time before the alarm is triggered when people are moving around a building but not trying to exit, through the fire alarm being triggered and then to the end of the evacuation when the building is finally empty. It supports multiple floor layouts and simulates pedestrian movement down a staircase.

The model runs at about 1/30th of real-time due to constraints of the Second Life scripting environment and physics engine. The main problem being that if the pedestrian's moved any faster than they currently do the physics engine in Second Life (Havok) tends to miss collisions and so the pedestrians start walking through walls and other barriers.

Layouts:

We have provided three predefined floor layouts in the model. Each of these is described on a below along with screen shots and a movie of a model run using that layout:

It is easy to create new layouts or modify existing ones either in the predefined scripts or by just dragging walls around in Second Life.

Model Components:

Each of the parts that make up the model are shown below and are flexible enough to allow most building layouts to be re-created:






PedTrace System:

To help validate the model we linked it to a custom built web application called PedTrace running on a web server outside Second Life via HTTP messages. The web server records the position and speed of each pedestrian every second of the model. PedTrace uses this data to generate movement trace images and two graphs: a time-to-exit graph and an average walking speed graph.

PedTrace provides a webpage overview of the current model run (shown below).





Technical Details:

A PDF document containing details about how the model was implemented is available to download:


Source Code:

The Linden Scripts for this model are covered by the GNU GENERAL PUBLIC LICENSE and are available to download below.
The Visual C# source code for the PedTrace web service has also been released under the GNU GENERAL PUBLIC LICENSE and is available to download below. You might need some knowledge of C# and ASP.NET to make this work.

If you prefer to get up and running more quickly we have a vending machine on nature island here that will give you a complete working copy of the model when you click on it (this is now depreciated):





Single Floor - Simple Layout

The first building layout is a 20m square room with a single exit door and no internal walls.





Below we show a movie of a model run using this layout. We also present the output from the PedTrace web application for the same model run.




Simple layout movie (Agents exiting the building)



Pedestrian paths (generated by PedTrace)





Pedestrian paths every second of the model run (generated by PedTrace)

Average walking speed every second (generated by PedTrace)


Number of pedestrian exiting every second (generated by PedTrace)







Single Floor - Complicated Layout

The second building layout is the same as the first but adds internal walls and tables as obstacles for the agents.



Below we show a movie of a model run using this layout. We also present the output from the PedTrace web application for the same model run.


SecondLife complicated layout movie



Pedestrian paths (generated by PedTrace)



Pedestrian paths every second of the model run (generated by PedTrace)


Average walking speed every second (generated by PedTrace)



Number of pedestrian exiting every second (generated by PedTrace)






Two Floors

The final building layout is the same as the second but adds another floor on top and connects the two with a staircase.

First floor of layout


Ground floor of layout


Below we show a movie of a model run using this layout. We also present the output from the PedTrace web application for the same model run.




Second Life multi-floor layout movie


Pedestrian Paths - First Floor (generated by PedTrace)






Pedestrian paths for the first floor every second of the model run (generated by PedTrace)



Pedestrian Paths - Ground Floor (generated by PedTrace)





Pedestrian paths for the ground floor every second of the model run (generated by PedTrace)


Number of pedestrian exiting every second (generated by PedTrace)

Average walking speed every second (generated by PedTrace)







Agent and Avatar Interaction

In this final model we demonstrate how agents can be responsive to avatars. For this we use a simple building layout with two tables. As with the previous simulations, one the alarm is sounded the agents exit the room. Avoiding each other and avatars if present.


Basic Room layout

Below we show a traces of a model run using this layout with no avatars and with an avatar. We also present the output from the PedTrace web application for the same model runs.

Pedestrian Paths - With No Avatar (generated by PedTrace)



Pedestrian paths for model with No Avatar every second of the model run (generated by PedTrace)

Pedestrian Paths - Avatar standing to the right of the table (generated by PedTrace)








Pedestrian Paths - Avatar standing to the right of the table every second of the model run (generated by PedTrace).





Pedestrian Paths - With no avatar every second of the model run (generated by PedTrace) and the simulation visualization of the model in SL



Pedestrian Paths - With avatar every second of the model run (generated by PedTrace) and the simulation visualization of the model in SL

Average walking speed every second (generated by PedTrace) with no avatar
Average walking speed every second (generated by PedTrace) with avatar



Number of pedestrian exiting every second (generated by PedTrace) with no avatar

Number of pedestrian exiting every second (generated by PedTrace) with avatar

Source Code:

The Linden Scripts for this model are covered by the GNU GENERAL PUBLIC LICENSE and are available to download below.

The Visual C# source code for the PedTrace web service has also been released under the GNU GENERAL PUBLIC LICENSE and is available to download below. You might need some knowledge of C# and ASP.NET to make this work.
If you prefer to get up and running more quickly we have a vending machine on nature island here that will give you a complete working copy of the model when you click on it (this is now depreciated):


No comments:

Post a Comment