handheld augmented reality

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The Handheld Augmented Reality
Project is supported by the
following institutions:



Christian Doppler Forschungsgesellschaft


Graz University of Technology




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Locoball (2007)


Locoball Logo


LocoBall combines multiple mobile small displays into a larger virtual game area. The idea is inspired by classical tiled display systems, but in this case of LocoBall those displays are mobile used as input devices too. Though not achieving a high resolution, the combination of multiple small handheld displays delivers an appealing possibility to create a quasi continuous display.

LocoBall uses a completely new type of user interface for the well known game concept of Pong. No buttons, stick, pens, etc. are required. The player simply moves his/her panel over the table in order to explore the game game area and to controll the paddle.

The hardware setup is very simple:

  • 5 PDAs
  • 1 Webcam
  • 1 WiFi Basestation
  • 1 PC


Here is how a typical game situation looks like (click for larger version):



The PDAs can be freely moved on the table without any restrictions due to cables

Controlling the Game

The interaction mechanisms are straightforward. Users move the handhelds left and right in order to orient the paddle, which is used to bounce the ball. Hence, there is no button-pressing involved. The whole game is controlled just by moving the handheld, and thus is extremely simple! The paddle itself holds a face with eyes. The eyes are always oriented towards the ball, to provide the user with additional information. This is needed because most of the time, the ball is not seen (…which causes excitement among the players). The ball is actually a "mama ball" with some kiddies following: the kiddies form a comet-like line, providing a nice indication of the ball movement.
The two opposite players are teamed up, and should beat the other team. A team has three lives to loose: once lost, the other team has won. Additionally, there is the fifth display, in between the "personal" displays of the players. This display can be moved around freely to provide extra information on the ball's movement in the centre of the playing field, and will hold extra game elements in the next version of the game. Such elements may include moving elements that bounce the ball or creatures that may do funny or unwanted things with the ball. The centre thus can also be used to make the game more advanced and allow for levelling the game to allow for longer game sessions.

Technical Setup

The LocoBall project is focused around the idea of using simple and low cost, off-the-shelf hardware to create a game with a tiled display with movable tiles. The software is split into a client part running on the handheld devices (PDAs) and a PC-based server that performs the tracking, data distribution and can run an optional large display for showing the current game state. The server uses a web cam that is mounted above the game board. Natural feature tracking detects the lit displays at sub-millimetre precision using a custom thresholding algorithm followed by a rectangle finder. A 2D homography matrix transforms the detected poses (position and rotation) of the displays into the virtual game space. All detected poses are written into a Muddleware (Wagner and Schmalstieg, 2007) database that is used to distribute the game state as well as static setup data. The client software running on the PDA connects to the Muddleware server via WiFi to read the shared game state and the PDA's current pose and can thereby adapt the camera view into the virtual game world. Consequently the player can freely pan and rotate his/her PDA over the game board always seeing accurately game-board aligned virtual content.

Here's the game from the server's point of view (overhead camera, click for larger version):



The large white square represents the complete game area. The 5 smaller white rectangles are the players' areas in which they can move their PDAs. The centre PDA can be moved by any player. The position of every detected PDA screen is marked with a red rectangle and a red cross in its centre. Green crosses show filtered and corrected positions since some PDAs are only allowed to move along specific paths (for gameplay rather than technical reasons).

Images from Game Sessions

Player controlling his/her paddle (click for larger version)


Two PDAs closely alligned (click for larger version)


Screenshot of Player 2 (click for larger version)


Screenshot of Player 4 (click for larger version)





A first Publication is currently in submission.



The game's novel concept can be best understood watching a video. Please select from below.

A video introducing the LocoBall game in action can be download in two different qualities:

  • High quality
    Filesize: 46 MBytes
    Resolution: 720x576
    Bitrate: 2700 kbit

  • Medium quality
    Filesize: 15 MBytes
    Resolution: 400x326
    Bitrate: 800 kbit





Project Team

General Idea: Ernst Kruijff, Daniel Wagner, Albert Walzer & Dieter Schmalstieg

Software Development: Daniel Wagner
User Interface Concept: Ernst Kruijff
Game and Visual Design : Albert Walzer
Music and Sound Design: Przemyslaw Kopczyk
Video narrator: Joseph Newman



copyright (c) 2014 Graz University of Technology