Introduction to Virtual Reality

After hearing a lot of buzz about VR (Virtual Reality), I thought it is time, I look closely into what it actually is.

Virtual Reality is a computer generated (thus virtual) environment which aims to be life-like. It is as if virtual things came to life.

After being extremely enthusiastic about this I searched about it more and found that Udacity is offering the course named as Introduction To Virtual Reality. So I decided to take that course. There have been some discussions in our Robotix group about buying a VR development headset and starting off a project under our makerspace labs. Since I am pretty keen about this, I thought of taking the udacity course so that I have a solid idea about what VR actually is and what all it takes to have a successful VR project before just jumping about in “coolness”.

Note: What follows after this is kind of like class notes for the above listed Udacity course.

Principles of VR

What makes VR, actually VR? The common features of VR devices include a pair of lenses, a high definition display, tracking hardware. But is the hardware it for VR? Nope, VR is all about creating a synthetic virtual world which requires smooth working of several hardware and software systems not just a headset.

There are various aspects in Virtual Reality like optics, displays, tracking, performance, and many more.

Optics

Since virtual reality headsets are held pretty close to the eye, it becomes really tough to actually see the image. That is the reason lenses are required. Lenses help to focus the light directly into the retina from a near eyed object. The image would also look magnified after going through the lenses. We can actually see individual pixels. Each manufacturer has to make the best trade-off between the field of view, focal length, optical distortion and finally cost. The lenses reduce the apparent resolution of the VR display and they increase the distortions in the VR display.

Displays

These displays should have very high resolution because the lenses magnify them and image resolution finally decreases when they hit the retina.

Ideally, resolution of the display should be around 160,000 by 160,000 for a full HD view but right now we haven’t achieved that stage and it is a long way to go.

The second most important component is having the display with low persistance. It means that instead of showing the full image, it only shows you a part of the image at a given time. Now the question arises, Why is it necessary?.

Low persistence is necessary because it eliminates motion blur which keeps the image clear from ground and also keeps it from smearing together.

Low persistence hides the pixels while they effectively change colour. This gives us sharp, consistant and believable images.

Tracking

Tracking allows the headset to know where you are in space. Most of the VR headsets rely on IMU (Inertial Measurement Unit). It enables high speed rotational tracking. Unfortunately they can’t tell where the object is located, but can only give information about rotation.

IMUs employ variety of positional tracking techniques like camera, lasers, precise clocks, magnetic fields, etc. This is an area of active research.

Challenges

The biggest challenge that VR faces is simulator sickness. Some VR devices give you headaches and make you feel dizzy.

What makes people uncomfortable?

Pretty much anything that is mis-matched between the body’s internal sense of motion and the data brain receives from your visual system. So if what you see doesn’t line up with what body feels, one can feel uncomfortable.

Major VR Platforms

There is a major explosion of VR companies in recent times. The major are:

3-DOF vs 6-DOF

DOF means Degree of Freedom. The 3-DOF VR devices can only tell where you are looking while the 6-DOF VR devices can tell where you are looking as well as your current location in 3D space.

3-DOF tracks the rotations along the X, Y and the Z axis.

6-DOF tracks the rotations along the X, Y and the Z axis. On top of that it can also track the position along X, Y and Z axis.

How IMUs Enable 3-DOF Tracking

A very popular IMU is the Sparkfun 9-DOF Razor IMU which has a gyroscope, accelerometer and a magnetometer in built. It takes data from all of those, performs fancy math and then gives us all the final data for the 9-DOF system.

Sometimes this IMU is in the phone and some times in the headset but no matter what a VR system requires a IMU.

Major 6-DOF Tracking System

Let’s see how the two major players do it.

  1. Oculus Rift: It uses a tracking system called Constellation. Rift has a large number of infrared LEDs. Each LED is blinking very very fast. There is also a separate camera placed on the desk or somewhere nearby. The camera catches these light patterns and the computer builds up a model. The program then tries to fit the 3D model it gets into the 2D model. By doing all of this, it can calculate all the data required for tracking 6-DOF system.
  2. HTC Vive: It uses LightHouse tracking system. Unlike Rift, this one uses infrared lasers. It measures the time it takes to sweep the lazer horizontally and vertically to determine the location of the headset. This is a similar technique like light houses which help ships navigate successfully by using time measurements and by using an embedded IMU.

Differences between mobile and desktop VR

Mobile Desktop IMU Tracking Optical & IMU Tracking Untethered Tethered Less powerful More powerful No additional hand controller Hand controller

VR Development Platform

VR applications are easy to develop with the help of Game Engine softwares like Unity which is a combination of both Code + Editor so as to reduce efforts and time.

A typical game engine often provides:

  • 3D Rendering
  • Physics
  • Sound
  • Scripting
  • Animation
  • Asset Management
  • And more…

There are many other game engines like Unreal Game Engine, CryEngine, Lumberyard in the market.

There are various native development tools which can be used like C++, OpenGL, DirectX if you don’t want to use a game engine. The major advantage of using these are very customizability but then one can to compromise on development time which can get pretty long. These set of tools are more useful when you are developing framework which others can use.

There is also WebVR but unfortunately it isn’t that powerful and missed on many features and is currently still under heavy development. Maybe in future it can be used.

The further course now touches how to use the Unity3D platform to develop VR applications.

This course was pretty interesting and I got to know some really good insights on what VR actually is. I think I will do more research about this and try and build a simple application on Unity3D before buying out the VR headset!


Originally published at www.bauva.com on March 12, 2017.