OE-2.1 Virtual Space & the Mechanics of Sight

What this is and why it exists

This course opens with human perception rather than with hardware, and that ordering is deliberate. Every display specification later in the syllabus exists to satisfy a limit of the eye.

Read it the other way round and headset numbers look arbitrary. Read it this way and they become predictions you could almost have made yourself.

Depth is the heart of it. Stereopsis — the difference between what two eyes see — is only one cue among many. That is why a flat photograph still reads as deep.

The vocabulary

• Virtual reality — the view is replaced.
• Augmented reality — the view is added to.
• Virtual space — the modelled space, before any hardware exists.
• Position — three numbers saying where something is.
• Orientation — three more saying which way it faces.
• Visual pathway — the route from light at the eye to a usable signal.
• Depth cue — anything that tells you how far away something is.
• Stereopsis — depth from the difference between the two eyes' views.

The mental model

Start with the distinction, because the two get spoken about together and are not the same. One adds to what you see; the other replaces it. Getting that firm now saves confusion in every topic below, because almost every design consequence follows from which one you are building.

A virtual space exists before any hardware does. It is an abstraction — positions, orientations, contents — and the whole subject sits on it. Being comfortable with it in the abstract is worth the effort, because it is what the hardware is trying to deliver.

Six numbers describe an object completely: three for where it is, three for which way it faces. Everything about motion sensing and interaction later reduces to measuring those six or changing them. That is a genuinely useful compression of a large part of the syllabus.

Navigation through a space you are not physically in is harder than it sounds, and the reason is the body. When you move through a real room, your senses agree. When you move through a virtual one while sitting still, they do not, and the body notices.

Then the eye. The optics and biology of seeing come before display hardware for a reason. Knowing the limits of the eye tells you which display specifications matter and which are marketing. A number beyond what the eye can resolve is a number you are being sold.

And depth, which is where this topic earns its place. You perceive distance from several independent cues: occlusion, relative size, motion parallax, perspective, shading, focus, and stereo separation. Stereo is only one. Close one eye and most depth survives, which tells you immediately that a headset supplying stereo has supplied a fraction of the problem. Work out which cues a headset can supply and which it cannot. The hardest problems in the field then stop being surprising.

What you should now be able to explain or do

Define augmented and virtual reality and say what follows from the difference. Describe a virtual space without reference to hardware. Say what six numbers fix an object's position and orientation, and connect that to tracking. Say why navigating a virtual space troubles the body. Outline the visual pathway and use it to judge a display specification. Name several depth cues and say which a headset supplies.

Check yourself