small trainthe invisible train

A Multi-player Handheld Augmented Reality Game | Daniel Wagner, Thomas Pintaric and Dieter Schmalstieg


The Invisible Train

The Invisible Train is the first real multi-user Augmented Reality application for handheld devices (PDAs). Unlike other projects, in which wearable devices were merely used as thin-clients, while powerful (PC-based) servers performed a majority of the computations (such as graphics rendering), our software runs independently on off-the-shelf PDAs - eliminating the need for an expensive infractructure.


The Invisible Train is a mobile, collaborative multi-user Augmented Reality (AR) game, in which players control virtual trains on a real wooden miniature railroad track. These virtual trains are only visible to players through their PDA's video see-through display as they don't exist in the physical world. This type of user interface is commonly called the "magic lens metaphor".

Players can interact with the game environment by operating track switches and adjusting the speed of their virtual trains. The current state of the game is synchronized between all participants via wireless networking. The common goal of the game is to prevent the virtual trains from colliding.

The success of the Invisible Train installation illustrates the advantages of our Studierstube software framework, a component-based system architecture that has been designed to accelerate the task of developing and deploying collaborative Augmented Reality applications on handheld devices.

Why Handheld Augmented Reality?

Augmented Reality (AR) can naturally complement mobile computing on wearable devices by providing an intuitive interface to a three-dimensional information space embedded within physical reality. However, prior work on mobile Augmented Reality has almost exclusively been undertaken with traditional "backpack"-systems that consist of a notebook computer, an HMD, cameras and additional supporting hardware. Although these systems work well within a constrained laboratory environment, they fail to fulfill several usability criteria to be rapidly deployed to inexperienced users, as they are expensive, cumbersome and require high level of expertise.

Since the early experiments in Mobile Augmented Reality, a variety of highly portable consumer devices with versatile computing capabilities has emerged. We believe that handheld computers, mobile phones and personal digital assistants have the potential to introduce Augmented Reality to large audiences outside of a constrained laboratory environment. The relative affordability of devices that are capable of running our software framework opens up new possibilities for experimenting with massively multi-user application scenarios - thereby bringing us closer to the goal of "AR anytime, anywhere".


Tweenwork Award 2004 (2nd place), sponsored by Gesellschaft für Informatik, Fachgruppe ANIS (Graphische Simulation und Animation).
Multimedia Transfer Award 2005 (winning project), sponsored by Universität Karlsruhe and Commerzbank Frankfurt. Press release (German).

Exhibitions / Demonstrations

Jun. 24, 2004
Yo!Einstein 2004. The following newspaper article (in German) appeared in Kurier on 7/25/04.
Aug. 8-12, 2004
SIGGRAPH 2004 Emerging Technologies Exhibition in Los Angeles, CA. Photos of the Invisible Train at SIGGRAPH 2004 are available here.
Sep. 2-27, 2004
Ars Electronica 2004 Festival and Exhibition in Linz, Austria. Photographs of our installation at the Ars Electronica Museum of the Future are available here.
Oct. 1, 2004
Beginner's Day 2004, orientation event for incoming students at Vienna University of Technology.
Nov. 2-5, 2004
International Symposium on Mixed and Augmented Reality (ISMAR 2004) in Arlington, VA.
Feb. 2-5, 2005
Imagina 2005 Trade Show and WIMA (Wireless Information Multimedia Application) Symposium in Monte Carlo. Photos of the Invisible Train at Imagina 2005 are available here
Feb. 14-18, 2005
LEARNTEC 2005 (Multimedia Transfer 2005 Booth #190) in Karlsruhe (Germany).
Mar. 12-16, 2005
IEEE Virtual Reality 2005 Conference, Bonn (Germany).
May 8-13, 2005
3rd International Conference on Pervasive Computing (Pervasive 2005), Munich (Germany).
June 22-26, 2005
Wired NextFest.2005, Chicago (USA).

Scientific Publications

Daniel Wagner, Thomas Pintaric, Florian Ledermann, Dieter Schmalstieg
Towards Massively Multi-User Augmented Reality
on Handheld Devices

Proceedings of the Third International Conference on Pervasive Computing (Pervasive 2005), Munich, Germany (to appear) [PDF]


Press Photographs

The following high-resolution images are made available for print or web media, provided that they are not used in advertising, in promotion of products, or in other sales materials. Please credit these images with "Courtesy of Vienna University of Technology."


Press Photo 01

Press Photo 02

Press Photo 03

Press Photo 04

Press Photo 05

Press Photo 06


(UPDATED!) Downloadable Media / Videos


Invisible Train Promotion Video (Oct. 2004)
Invisible Train Promotion Video /videos/invisible_train.avi
38.9MB AVI (XviD Codec with MP3 audio)
720x576 pixels, 2 Mbit/sec, 25fps (PAL)
Invisible Train Promotion Video /videos/invisible_train_small.avi
9.2MB AVI (XviD Codec with MP3 audio) (reduced quality)
352x288 pixels, 400 KBit/sec, 25fps (PAL)
Invisible Train Promotion Video /videos/invisible_train.mp2
41.3MB MPEG-2
720x576 pixels, 2MBit/sec, 25fps (PAL, DVD compliant)
Invisible Train Promotion Video /videos/invisible_train_small.mpg
24.5MB MPEG-1 (reduced quality)
352x288 pixels at 25fps (PAL, VideoCD compliant)



website maintained by Thomas Pintaric
last updated on 6/6/05

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