How VR works

Virtual Reality is a topic which is very interesting for me and I have invested a fair amount of my spare time since last summer in learning more about the subject. Right at this moment, I’m in the middle of a 6-week edX-MOOC from UC San Diego „How Virtual Reality works“.
For sure, it would be nice to get a certificate – but since my last edX MOOC, edX has changed its policy, so that now there are only verified participation certificates for a fee that varies by course (in this case 99 Dollars). In order to get it, there would be many assignments – among them quizzes, engagement tasks (video watching and marking as complete etc.), discussions and project tasks with peer review. The weekly short videos are very informative and don’t cost a lot of time whereas the project tasks did cost me a lot of time and I’m no big fan of peer reviews. I would have preferred forums where I could choose which answers I would like to read and engage with instead of getting 3 submissions with a lot of (formal) questions and points between 0-3.

What’s the content of this MOOC? In the beginning, I thought it was about WebVR, but until now WebVR is in the optional course sections. But there was already a lot of background theory relevant for VR:

  • week 1: Introduction to and History of VR  & The Human Visual System and Display Methods
  • week 2: Input Devices: Degrees of Freedom and Tracking
  • week 3: Selection and Manipulation

Regarding a definition of VR, there are 3 defining elements: Virtual World (can resemble reality or be fictional), Interaction, Immersion. Today, VR is present in many differenct industries, but gaming is still the  dominant driver. I was astonished to hear that the first HMD „Sword of Damocles“ goes back to the 1960s (it was so heavy it had to be attached with a mechanical arm from the ceiling). Until the 1970s tracking was done mechanically with arms anchored in floor or ceiling, 1979 followed the first electromagnetic system (tracking over longer distances and without mechanical arm) from the company Polhemus and the first data gloves came in 1985. In the 1990s, walk-in VR systems (caves) were invented and mostly used electromagnetic or ultrasonic tracking. 2002, optical tracking systems became available (thanks to Hollywood) and the development of smart phones led to their use as screens for consumer VR devices many years later. In 2016, there were HMDs like Oculus Rift CV1 and HTC Vive, Sony Playstation VR and Microsofts Hololens.
The part „Human Visual System“ was a little bit harder to follow: Monocular depth cues like occlusion, linear perspective, shadows, motion parallax and accomodation aren’t a topic you often hear or think about. Regarding human eye specs, there are some parameters of the eye which are important for VR: color and field of view (220 degrees from both eyes, but binocular vision for 3D stereo is just 120 degrees). We also heard about active stereo, passive stereo and autostereos optic displays (wearing glasses not necessary).

Input devices for 3D VR environments are special (you can’t just use a mouse) and you have to think about Degrees of Freedom (DOF), e.g. the ways an object can move within a space. There are 6 DOF in a 3D space which can be divided in 2 categories: translational (left/right, forward/backward, up/down) and rotational (pitch, yaw, roll) movements. You have also to distinguish between position and orientation and know about relative and absolute DOF – absolute positioning devices use a direct mapping between control space and virtual space.
There are different tracking systems for VR: Mechanical tracking (can’t be used for walk-around VR applications), electromagnetic tracking (also with range limitations), ultrasonic & inertial tracking (components gyroscopes and accelerometers), optical tracking (became popular for motion capturing in Hollywood movies). The least expensive way to do VR is with smartphones but that doesn’t allow for positional tracking (only the head orientation is tracked).

The course section „selection and manipulation“ was easier to follow for me because of personal experiences with VR. Selection means the option of picking one of many objects in VR, manipulation means the action afterwards which modifies an object or makes changes to the virtual world. Both depend heavily on the capabilities of the interaction device which is used.
Important for effective selections are: how far away is the object? what size is the object? the density of objects (and are there obstacles) around the object which shall be selected? the accuracy of the tracking device?
Manipulation of VR objects can mean positioning them (moving them around) or rotating them – in the real world we are used to 6 DOF, but few controllers are able to do that.
Selection and manipulation interaction techniques for VR can be isomorphic (mimic the real world) or non-isomorphic („magic“ – not limited to laws of physics but therefore might not be intuitive). There is also the distinction between egocentric (user is at the centre, real hand = virtual hand, Go-Go technique, Laser pointer or Flashlight technique etc.) and exocentric (world in miniature approach, voodoo doll approach etc.) interaction methods. As low-cost VR solutions like smartphone & Cardboard don’t have controllers, selection and manipulation track the user’s head direction – the head gaze typically controls a cursor in the center of the screen and via head movement the cursor can be moved to select a predefined object. Manipulation often is simply done by hovering the cursor over an object for a certain amount of time (2 seconds or so) which then triggers an action. Hand gestures would be the most natural way to interact in VR (devices like Leap Motion or Microsoft Kinect which can detect finger pinches), but there is still the issue of not providing haptic feedback when touching an object.

This covers my impressions of week 1 to week 3; hopefully there are no big mistakes in my notes.

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