Inthis class, we use the VRduino together with HTCs official Lighthouse base station as the light source. It also has a micro-controller attached to them, so we can implement all computations for pose estimation on the VRduino directly. The VRduino has 4 photodiodes similar to those used by HTCs VR controllers and headsets. Using these measurements, one of several optimizationtechniques can be employed to estimate the 6-DOF pose of the tracked device with respect to the base station.For more information on the Lighthouse and its communication protocols, refer to the unofficial documentation at. The photodiodes are fast enough to time-stamp whenthe laser sweeps hit them relative to the last sync pulse. It does that very fast 60 times per second for afull horizontal and vertical sweep with sync pulses in between. Specifically, the Lighthouse projector or base station sweeps horizontal andvertical laser stripes across the room, hence the name lighthouse. HTC calls their technology Lighthouse and it usestemporally-structured illumination. , who used spatially-structured illumination. An early paper on this technology was published byRaskar et al. The projector emits structured illumination to help the photodiodes determine theirown 2D location in the reference frame of the projector. The camera is replaced by a projector and instead of LEDs, photodiodesare mounted on the device. The HTC Vive also uses an optical tracking system, but rather than using a camera to observe LEDs on the headset,the Vive uses a slightly different approach. This problem is known as theperspective-n-point problem and of importance in camera calibration, 3D computer vision, and other fields. The arrangement of the markers on thetracked device is usually known from its design or calibrated by the manufacturer. The pose of HMD or controller is then estimatedfrom the measured locations of the LEDs or markers in the camera image. In optical tracking, one or more cameras observe a set of referencepoints, for example infrared LEDs or actively illuminated retroreflective markers mounted on a VR controller or aheadset (e.g., Oculus Rift and Sonys Playstation VR headset). The most widelyused technology, however, is optical tracking. Commercially-available systems includemechanical trackers, magnetic trackers, ultrasonic trackers, and GPS or WIFI-based tracking. Positional tracking can be implemented with a variety of technologies. The goal of 6-DOF pose estimation is to recover the relative position (three degrees of freedom) and rotation (anotherthree degrees of freedom) of some rigid object, for example a headset, a controller, or the VRduino, with respect tosome reference coordinate system, such as that of a camera. The document is not meant tobe a comprehensive review of positional tracking for virtual reality applications but rather an intuitive introductionto the basic mathematical concepts of pose estimation with the VRduino. This document serves as a supplement to the material discussed in lectures 11 and 12. EE 267 Virtual Realitåourse Notes: 6-DOF Pose Tracking with the VRduino
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