Virtual Haptic Radar: touching ghosts
The Virtual Haptic Radar (VHR) is a wearable device helping actors become aware of the presence of invisible virtual objects in their path when evolving in a virtual studio (such as a "bluescreen" filming stage). The VHR is a natural extension of the Haptic Radar (HR) and its principle in the realm of virtual reality. While each module of the HR had a small vibrator and a rangefinder to measure distance to real obstacles, the VHR module lacks the rangefinder but accommodates instead a (cheap) ultrasound-based indoor positioning system that gives it the ability to know exactly where it is situated relatively to an external frame of reference. Each module maintains a simplified 3d map of the current virtual scene that can be updated wirelessly. If the module founds that its own position is inside the force field of a virtual object, it will vibrate.
It is important to understand that the requirements for our tracking system are fundamentally different from that of traditional (optical or magnetic based) mo-cap systems: (1) each VHR module must know its own position in the room, independently from the others and without the need for a centralized computer; (2) the tracker must be inexpensive in order to enable scalability; (3) the modules must be invisible to the cameras (in particular, they should not emit or reflect visible light); and (4) interference should be minimal or inexistent if one wants tens of modules to work simultaneously (this puts aside most non-sophisticated magnetic trackers).
With these considerations in mind, we first considered optical based methods such as Prakash [Raskar and al. 2007], which have been shown to satisfy all these constraints. However, we eventually preferred to develop a custom system based on ultrasonic triangulation and radio synchronization (the main reason for this choice being avoiding a complexity of the spatio-temporal structured optical beacon). Our prototype simply consists on 2 to 8 ultrasonic beacons emitting bursts every 15ms. A radio signal synchronizes receivers with the start of an ultrasound sequence. The receivers, concealed under the clothing, contain a micro-controller that computes the difference of arrival times, triangulates its own position and determines the adequate level of vibration. We successfully demonstrated this cheap solution for virtual object collision avoidance in a plane about 4x4 meters wide.
Future work will aim to decrease directivity of the ultrasonic beams which was shown to limits the range of movements of the user as well as improving the triangulation algorithm in order to compute height.
- A. Zerroug, A. Cassinelli & M. Ishikawa, Virtual Haptic Radar, submitted poster for SIGGRAPH ASIA 2009, Yokohama. One page abstract [PDF-366KB]
- More complete webpage here: http://www.k2.t.u-tokyo.ac.jp/perception/VirtualHapticRadar/