Imagine if everything you pointed your phone at - from people to pets, shops to mountains - had its own 'bubble' of information. It sounds like science fiction, but augmented reality is already here.
It's an average city street: buildings, buses, people with shopping bags. Suddenly information bubbles pop up in your field of vision. The woman over there is called Jane and right now she's listening to Florence and the Machine on her iPod; you don't know her but you have five mutual friends on Facebook.
The building opposite was built in 1932, is 31m tall and down the road is the boarding school Russell Brand went to. In the alleyway 10m behind you, there was a mugging at 1.15am last Wednesday, two streets away TopShop is having a sale and their summer range is reduced by 20 per cent, there are 14 coffee shops in a one-mile radius, and the flowerbed to your left has won "the most imaginative civic planting" award four times in a row.
If Arnold Schwarzenegger's Terminator had walked through, say, Bishop's Stortford, this is the sort of information his computer-enhanced vision might have provided.
But "Terminator vision" is no longer just in the realm of science fiction films. It's called augmented reality and it is on its way to a smartphone near you. Complete Terminator vision would require bionic contact lenses ... but from this month, anyone with an iPhone will be able to peer at the world through the phone's camera and will see layered on their phone screen extra information about the physical things in front of them. Those with a phone that supports Google Android can already do this.
Virtual reality used to be technology's Holy Grail. It let you create new worlds where you can jack cars, date babes and win wars. In contrast, augmented reality - in which computer graphics are layered onto a real world image - was the boring sub-technology confined to sports footage replays and technical engineering.
That's what shows you the path of a tennis ball after a player has hit it, or demonstrates to an engineer how to piece a complex machine together by modelling it in 3D.
But with augmented reality about to be opened up to the mobile phone-owning masses, it has become an exciting field for development. Developers are racing to find useful and interesting ways that computers can enhance our interaction with the real world. And that could be by superimposing reviews on restaurants, directions on streets and Facebook profiles on people. It could be trivial, it could be fascinating. Perhaps the most useful application hasn't been figured out yet.
The technology that has brought augmented reality to mobiles is called Layar. As the name suggests, it layers computer information on top of "reality" as seen through the phone's camera. Layar uses the phone's Global Positioning System (GPS) to work out where you are and what you are looking at.
Different types of information appear on different layers: there's a sightseeing layer called Wikitude which contains tourist information about what's around you - the posts are linked to specific buildings and points of interest (the Tate Liverpool, the Belfast docks, Big Ben) and pop up, like virtual blue plaques, as you pass by them.
There's an estate agent layer which flags up properties for sale or rent: as you scan your camera down a street, available properties are highlighted. Of course, a board outside a house would tell you as much, but the layer, called Trulia, will also tell you how much the house is going for, give you pictures of the inside and a phone number that you can ring to arrange a viewing.
You don't only see things in your viewfinder - properties two streets away will show up too. There's a layer which tells you where the nearest council facilities are and plots them on an image of the street.