What are VR, AR and MR?
- Virtual reality (VR): you see only a computer-made world. The real world is blocked out.
- Augmented reality (AR): you see the real world, and the computer adds objects, text or arrows on top.
- Mixed reality (MR): virtual objects are fixed in the real room and can react to real things, like hiding behind a real table.
All three together are called extended reality (XR).
How a VR headset works
- Two pictures (stereoscopy): our eyes are about 6 cm apart, so each sees a little differently. The headset draws two images from two virtual cameras. The brain merges them and feels depth.
- Lenses: the screens are only a few cm from the eyes. Lenses make them look far and wide, filling our view (field of view).
- Tracking: gyroscopes and accelerometers sense head turns; cameras sense position. The computer redraws the scene for the new view.
- Speed: the picture must update about 90 times a second with very little delay (latency). Slow updates make people feel sick (motion sickness).
Controllers, hand tracking and headphones add touch and sound.
How AR works
- The camera captures the real world.
- Software finds features: a printed marker, a flat floor, a face or a GPS location.
- It works out where the camera is and how it is turned (tracking).
- It draws the virtual object in the right place and size, and keeps it there as you move.
Examples: face filters, navigation arrows on the road, games that place creatures in a park, a doctor’s view of veins.
Applications, benefits and risks
Uses: games and films; training of pilots, drivers, soldiers and firefighters; surgery practice and therapy; architecture and product design; virtual tours and classrooms; shopping (try on glasses); factory repair with step-by-step AR guides.
Risks and limits: motion sickness and eye strain, less outdoor activity, privacy (cameras record your space), safety (bumping into things), cost of headsets. Use VR in short sessions with a clear space around you.
A simple AR project
- Plan: choose what to add, e.g. a 3D model of a planet that appears on a printed picture.
- Make the content: a 3D model (made in a 3D tool) or a picture/video.
- Choose the trigger: a marker image, a flat surface or a QR code.
- Build with a free block-based or web AR tool: link the trigger to the content.
- Test on a phone in different light, and improve size and position.
Try it: see stereo with your own eyes
Hold a finger 20 cm in front of your face. Close the left eye, then the right eye, again and again. The finger jumps. Each eye sees a different view: that is exactly the trick a VR headset uses. Then in the 3D, turn the head slider and watch the image move the other way.
Key formulas and definitions
- VR: virtual world replaces the real one
- AR: real world + virtual layer
- MR: virtual objects interact with the real world
- Stereoscopy: two images, one per eye → depth
- Frame rate ≈ 90 frames per second; time per frame = 1/90 s ≈ 11 ms
- Tracking: rotation (3 DoF) or rotation + position (6 DoF)
Worked examples
1. A game shows a dragon flying over your real school field through a phone camera. VR or AR?
AR. The real field stays visible and the dragon is added on top.
2. A headset runs at 90 frames per second. How long is each frame?
1/90 s ≈ 0.011 s = 11 ms. The computer must draw both eye images within 11 ms.
3. Why does a VR headset need two images instead of one?
Our eyes are about 6 cm apart, so each sees a slightly different view. Two images copy this, and the brain turns the difference into depth.
4. A trainee surgeon practises an operation on a virtual patient. Give two benefits and one limit.
Benefits: no risk to a real patient; mistakes can be repeated and learned from. Limit: the feel of real tissue (touch) is hard to copy, and good systems are costly.
Common mistakes
- Calling a phone filter "VR": it keeps the real world, so it is AR.
- Thinking the screens are far away: they are a few cm from the eyes; lenses make them look far.
- Forgetting that slow updates (high latency) cause motion sickness.
- Ignoring privacy: AR apps use cameras that can record people and places.