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You've got to get to an unfamiliar part of town. How do you find the way? You asked for directions but the instructions you were given are confusing. You're tired of getting lost and of asking for directions from passers-by, many of whom don't know their left from their right. You wonder why it is that men landed on the moon in 1969 yet advances in technology haven't solved the challenge of getting around as a blind person. Or have they? What's this GPS thing that people have on battlefields, in their cars and on boats? Doesn't it give people directions? Could visually impaired people use this technology? Good thought! Let's take a look at the reality behind GPS as a solution in practical terms ...

GPS stands for Global Positioning System. It can tell people where they are anywhere in the world. Signals are transmitted from satellites orbiting the Earth. A GPS receiver, which you carry, picks up these signals, decodes them and calculates where you are. A computer can then plot your position on a computerised map and work out a route from where you are to where you want to go. Some drivers use GPS to help them find their way.

You need a GPS receiver. Some modern receivers can work alone, but these are not accessible to blind people. So, you'll also need a computer, the special GPS software and digital maps, and a speaker or earphones.

Pulsedata International sells the and GPS devices.
• Visuaide will shortly be releasing the Victor Trekker, which will run on a notetaker or handheld computer.

No. GPS will tell you where you are and where you need to go, but it will not stop you bumping into things or falling down holes. So you still need your long cane or guide dog. Other technologies do exist to help you avoid obstacles, these include the Miniguide, the and, for blind wheelchair users, there is the .

GPS combined with computerised maps has the potential to give visually impaired people access to street plans, information about where they are and instructions for how to get anywhere. For example, if you want to meet your friends in a restaurant across the other side of town and you've never been there, GPS can guide you there using spoken instructions.

Yes. It will tell you where you are, the direction you're going in, what points of interest are close by and which way to go. So on your way to the restaurant it will tell you your location, what you are passing, where to turn, when you reach the bus stop and anything else you need to know to find your way.

As well as the layout and names of streets, the maps include some buildings, such as train stations, museums and shopping centres. These are known as points of interest on the device. You can add your own points of interest as you find them. For example, you could add your friend's house so that in the future you can choose it as a destination or find out how far away from it you are.

GPS has the potential to make a big difference to the way blind people get around. However, there are a number of practical problems - though some of these problems will become less significant as the technology is developed. A couple of years ago GPS required a laptop, which was bulky and heavy, but now it can run on some smaller notetakers and handheld computers. The cost is also coming down.

GPS can be accurate to within ten metres. However, in practice the accuracy is often less than this. You may be several metres away from where the system tells you that you are. For example, on your way to the restaurant the GPS might tell you to turn a street too soon or too late. Satellite signals can be blocked by tall buildings or trees, and generally cannot be received in buildings such as train stations and shopping centres. If the signal is lost, the system cannot give you information about where you are. So, for example, suppose you were almost at the restaurant and the signal got blocked, the system would not be able to tell you when you arrived at the restaurant.

Will these problems be solved in the future? Possibly. Future direction-finding solutions may involve G3 mobile phone technology, whose signals are largely not deterred by buildings.

The maps are generally designed for drivers and are not designed with the needs of blind pedestrians in mind (though there are some exceptions). So, when the computer works out a route for you it may not be possible to walk that precise route. It may tell you to walk along a busy road that has no pavements or you may need to cross a road that has railings in the middle of it to stop people crossing. It will not give you information such as where to find pedestrian crossings or whether a pavement is a shared pedestrian and cycle way. The system cannot help you find an entrance to a specific building unless it is marked as a point of interest. So, the restaurant where you are meeting your friends might not be on the map. You could choose the street as your destination, but once you arrived at the right street the system might not be able to help you find the place itself. These are just a few examples.

The points of interest can be useful but they are limited. For instance, if you get to the restaurant and meet your friends, only to discover that the restaurant is full, you might want to find out where the next nearest eatery is. The system may tell you that it is five miles away, because that is the closest one included on the map, but you may unknowingly be standing just round the corner from one that the system doesn't know about.

So, is GPS the solution to guide you to an unfamiliar part of town? For some it is, but many others will go on asking passers-by for directions. Whether GPS or people give you directions, you'll get to where you need to go. But me? "Taxi!"

Yes. Choose your destination and the computer will work out the route. You can then read the directions and find out all about the route you'll take. So, using the restaurant example, you'd type in the name of the restaurant or choose it from a list and the computer would work out the way. You could then read the instructions, find out which bus to take and how far you'll have to walk. If you wanted, for example, to post a parcel on your way you could even find out whether you go past a post office.