Real-time content projection onto a tunnel from a moving subway train

Abstract

In this study, we present the first actual working system that can project content onto a tunnel wall from a moving subway train so that passengers can enjoy the display of digital content through a train window. Our stand-alone system can be easily deployed to existing trains because it does not assume any specific type of interface requiring data transfer with the train. To effectively estimate the position of the train in a tunnel, we propose counting sleepers, which are installed at regular interval along the railway, using a distance sensor. In the preprocessing step, the side depth variation along the tunnel is stored in synchronization with the train location in a tunnel profile. The tunnel profile is constructed using pointclouds captured by a depth camera installed next to the projector. The tunnel profile is used to identify projectable sections that will not contain too much interference by possible occluders. The tunnel profile is also used to retrieve the depth at a specific location so that a properly warped content can be projected for viewing by passengers through the window when the train is moving at runtime. Here, we show that the proposed system can operate on an actual train and evaluate the quality of the projection results through simulation.