A location-based game with audience participation

Thomas Wagner & Tiago Martins, 2008

Wolves and Sheep


Wolves and Sheep (WaS for short) is a location-based game that augments a real physical space, in which players physically move as if they were pieces on a game board. Players physically navigate the real world to achive their objectives, and this requires the game’s mobile interface to focus on sound and haptics as alternative channel. In this way the player can safely navigate an urban space, keeping the focus of her sense of sight in the real world.


In WaS one can play as a Wolf or as a Trapper. The Wolf’s objective is to catch as many (virtual) sheep as possible to feed its pack. The Trapper’s objective is to obtain as many wolf skins as possible from the (virtual) wolf packs. In addition, audience participation is encouraged via an overview map interface.


When playing a Wolf, the player incarnates the alpha leader of a virtual pack of hungry wolves. The player’s objective is to keep the wolves from starving by leading them to a lonely sheep. To discern the location of the sheep, the Wolf must rely more on his senses of smell and hearing than the sense of sight.

When playing as Wolf, the player uses a mobile phone as interface. The phone’s screen will show a map representing the game space as mixture of real and virtual elements. The map only shows a radius of less than 80m around the player. To locate the sheep, the player must resort to his Wolf senses. All the while the player will be able to hear the sheep’s bleating, which will get louder the closer he gets to it. Also every few minutes the player can try and use the Wolf’s sense of smell, which will briefly show on the map a very approximate direction towards the sheep. The sense of smell can be affected in several ways during the game, namely by power-ups the player acquires or by in-game environmental conditions.

Besides dealing with real physical constraints (a wall or building in his way) the player must also deal with virtual bodies of water. The pack will refuse to cross these and so the player must find alternative routes for them. Once both the Wolf and the pack are in sufficient range of the sheep, the pack will devour a sheep. Their hunger meter decreases and the hunt for a new sheep begins.


Provided there is a reasonable enough number of Wolf players, one or two players can join in as Trappers. The Trapper’s objective is to gather as many wolf skins as possible. These are dropped by wolf packs when one of their members dies – either of starvation or by the Trapper’s own hand. To accomplish this he relies on his skills in stealth, tracking, setting traps and (if all else fails) the hunting knife.

When playing as a Trapper the player uses both a mobile phone and a special bracer (the Gauntlet) as interfaces. The mobile phone will show a map, similar to the one a Wolf player sees but with a wider view. The Trapper cannot attack Wolves themselves and he will be repeatedly bitten whenever he gets close to one. Instead he targets the (virtual) wolf packs. To avoid being seen on the map and attacked by a Wolf, the player must literally sneak, moving somewhat slowly and cautiously. A Trapper can find the direction of a wolf pack by pointing around. The presence of a pack in a given direction is signaled by a rumbling of the Gauntlet. He can set a limited number of traps to damage and hinder a pack. This is accomplished by repeatedly making a circular motion with his hand towards the ground. If the player is close enough to a pack of wolves, he may attack the pack by making stab with his faithful hunting knife – which is a real physical object but actually nothing more than a harmless prop.


The game state and its evolution can be both observed and influenced by the audience at one or several locations. In the first staging of WaS we used a tangible interface for this purpose. The interface consisted of a surface on which a hybrid map of the game space and physical space is projected and where physical markers can be displaced to influence placement of power-ups and in-game environmental conditions. The position of power-up spawners and weather zones would be tied in real-time to the (dis)placement of these markers upon the projected, real-time game map on the surface.

Technical Details and Production

The first version of Wolves and Sheep was staged as part of the Interface Culture – Art on The Move Exhibition during Ars Electronica Festival 2008. This version was produced by the authors alone over a span of four months.

In order for WaS to be played by several players at once, the system is based on a client-server architecture. The server is then responsible for managing the game logic and state, communicating with the mobile phone clients and also the public interface.

Game Server

The game server is entirely coded in Java. It maintains the game state and runs the game logic based on this information. The game state can be affected by the client software running on the mobile phones. Updates are periodically exchanged between clients and server via the TCP protocol. The game server also hosts and interfaces with the public interface software. Values pertaining to the server’s functioning and game rules (such as pack speed, power-up durations, game map and others) are stored in a text configuration file and so can easily be altered or swapped.

Phone Client

The client software running on mobile phones (currently Nokia N95 models with 8Gb storage space) is a light-weight client, relaying all the game logic and bookkeeping to the server to focus on input and output processing. The client was written using Python for Series 60 which allows (among other things) for rapid prototyping of applications which use the phone’s pripherals – such as the embedded GPS module which is responsible for keeping track of players.


The Gauntlet is a special device, a wearable interface for pervasive gaming focusing on gestures and usage of real objects in ubiquitous gameplay scenarios. A full description will soon be found here.

Public Interface

The public interface consists of a setup similar to the RecipeTable. The reacTIVision framework (Java library) was used as part of the game server in order to recognize fiduciary markers through captured video from an IDS industrial grade camera.


For staging Wolves and Sheep at the Interface Culture – Art on The Move Exhibition during Ars Electronica Festival 2008 we had the kind support of:

Nokia Österreich



IDS – Image Development Systems

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