VR equipment

Virtual reality High-end user-computer interface Real-time simulations and interactions Multiple sensorial channels: visual auditory tactile smell taste Simulation in which computer graphics is used to create realistic-looking world. Not static, but responds to user’s input. Key feature: interactivity Interactivity and captivating power of graphics contribute to feeling of immersion.

Three I’s Extent to which simulation solves problem is dependent on imagination. Imagination also refers to mind’s capacity to perceive non-existent things, such as this triangle (after Kanizsa).

History 1960: Heilig patents head-mounted display (for slides) 1962: Heilig patents Sensorama (VR video arcade) 1966: Sutherland builds CRT-based HMD 1973: Evans & Sutherland design graphics accelerator 1981: NASA develops LCD-based HMD 1985: Zimmerman & Lanier develop sensing glove 1993: IEEE organizes first VR conference Sensorama: 3D video, motion, color, stereo sound, aromas, wind effects (using fans), vibrating seat. Possible to simulate motorcycle ride sensing wind, feeling pot-holes, smell food passing by store. Evans&Sutherland: precursor of modern graphics accelerators; framerate 20/s; 200-400 polys. NASA: ripping apart Sony Watchman TVs; special optics to allow focussing

VR survival: PC vs. high-end SGI Drawback of early VR: expensive (SGI Reality Engine > $100.000 in ’93). Expectations to high due to media hype; VR could not deliver overnight and funding dried up. Mid-90s critical because focus was on Internet and Web apps. Rebirth late 90s: CPU speed, PC-based graphics accelerators. Also due to large-volume displays (instead of HMD).

Components

Input devices 3-D position tracking devices Navigation and manipulation devices Gesture interfaces

Tracker performance: Accuracy Difference between actual position and measured position Separately given for translation and rotation. Not constant, and degrades with distance from the origin of coordinate system. Resolution: granularity of minimum change in position that can be detected Repeatability: relates to jitter (next slide)

Tracker performance: Jitter Change in tracker output when stationary (sensor noise) No jitter -> constant value for stationary object. Needs to be minimal to avoid tremor, jumpy objects, etc. Also not constant and influenced by environmental conditions near tracker.

Tracker performance: Drift Increase in tracker error with time Inaccuracy grows over time (stationary object shown). Controlled by zeroing, using a second tracker that has no drift. Typical of hybrid trackers (not discussed).

Tracker performance: Latency Time delay between action and result Can induce motion sickness.Elements: measure object change, communication time between tracker electronics and host computer, time to render scene. Sync tracker and communication with display loop (genlock).

Tracking devices Mechanical Ultrasonic Optical Magnetic

Mechanical trackers high accuracy low jitter no drift low latency Drawbacks: limited range weight limited freedom of motion few mm, 0.2 microseconds latency Larger: inertia and weight increase resulting in mechanical oscillations

Ultrasonic trackers high accuracy acceptable jitter no drift high latency Drawbacks: very limited range direct line of sight required background noise corrupts signal Based on triangulation; 3 microphones and 3 speakers; speakers activated in cycles, 3x3 datasets, derive pos and orientation. Update rate low, wait 5-100 ms to allow echoes to die out. 1,5 m range (air absorpts signal)

Optical Trackers high accuracy low jitter no drift low latency Drawbacks: direct line of sight required environmental reflections IR sources corrupt signal 0.5 mm, 0.03 deg.

Magnetic trackers high accuracy low jitter no drift low latency Drawbacks: limited range electromagnetic devices corrupt signal metallic objects corrupt signal Three antennas formed of three orthogonal coils wound on ferromagnetic cube. Excited sequentially. Intensity of signal falls with cube of distance. 2.5 mm, 0.5 deg

Navigation and Manipulation Devices Wanda Cubic mouse 5DT Data glove

Wanda

Cubic mouse 9x9x9 cm with tracker. translating rods can be pushed in and out, 6 buttons. Designed for manipulation of single large model.

5DT Data Glove Gesture interface measures position of fingers (sometimes also wrist) to allow gesture-recognition based interaction. Here: one sensor per finger and tilt sensor to measure wrist orientation. Finger bending measured based on intensity of returned light emitted from LED. Fiber walls change index of refraction upon finger flexion. Thumb not used: 2^4 = 16 combinations for gestures.

Output devices Stereo issues Graphics displays Haptic displays

Stereo vision Field of view in humans: 180 (H) by 120 (V) degrees Stereopsis (binocular overlap): 120 degrees Interpupillary distance: 53 – 73 mm

Active stereo

Passive stereo

Graphics displays Head-mounted Floor-supported Desk-supported Large-volume Projector-based

Fishtank VR 3D Display 2D Input 1D Input 3D Input

Projection-based displays Single display Theatre TiledWall CAVE (4- and 6-sided) FlexWall

Workbench

Dual Workbench

Theatre (curved screen)

TiledWall

CAVE (Cave Automatic Virtual Environment Uni. Illinois 1993)

Reality Cube (Cave) Zernikeborg Theater

CAVE computer graphics issues

FlexWall

Next lecture OpenGL pipeline Graphics hardware Scenegraphs (Performer)