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Developments in Wayfinding for Blind Pedestrians

Dr. John Gill
July 2004


Traditionally a blind person has relied on a guide dog or a long cane to navigate the environment. With the introduction of new technologies such as real-time passenger information systems, there are an increasing number of ways to help blind travellers for which the additional cost is not prohibitive. However there is a lack of consensus on the optimum strategy.

Journey planning
A typical journey will involve more than one mode of transport; for example it might involve:

Working out the optimum combination may not be a simple task since it may be a function of price, times of public transport and accessibility aspects. At present there is no generally available information service that provides a comprehensive service for journey planning including accessibility aspects.

The journey
The environment in which we live is becoming increasingly complex. Even journey across a city by bus requires a range of skills including:

Being able to avoid obstacles on the pavement

These tasks may seem trivial, but for someone with no useful vision they are skills which have to be learnt. Even for someone with low vision, all these tasks are less easy than for someone with normal sight.

Electronic mobility aids
Over the last thirty years, engineers have devoted considerable resources to developing electronic systems to help a blind person avoid obstacles. The most common approach has been to use ultrasonics; as with radar, the range is obtained from the length of time it takes for a pulse to be reflected back to the transceiver. Other systems have used lasers or infra-red.

Many of the devices just provided information about the range of the nearest object; a 'picture' could be built up by moving the sensor from side to side. Other devices have attempted to give a more complete image of the environment but at the expense of providing an excessive amount of information to the blind user.

The main problems are not in designing the electronic circuitry for a satisfactory electronic mobility aid but in:

The capacities of the senses of hearing and touch are very small compared to that of the visual channel for a human. Therefore selecting and processing the information to make best use of the non-visual channels is not a simple task. The sensors in future devices are likely to involve more than one modality (eg both a video camera and an ultrasonic transceiver) in order to obtain the necessary data which can be processed to produce an accurate image of the immediate environment. However the research that has been done on the automatic processing of satellite pictures and the research on neural networks offer hope that significant advances could be made in the next few years.

Embossed maps
For a blind person, the problem of getting about is not just that of not walking into objects. One problem is that of knowing the layout of the environment; here, an embossed map can help. However embossed maps are not easy to produce or interpret since just embossing a sighted map seldom leads to an intelligible embossed map.

The problem of converting a sighted graphical representation to an embossed one can be illustrated by the problem of indicating direction. Visually it is often shown as an arrow on a line. An embossed arrow gives a sense of direction at only one point on the line and the symbol is unfamiliar to many blind persons. However a line sawtooth in cross-section has an indication of direction over the whole length of the line, and it is easy to associate the symbol with the meaning since the line is smooth in one direction and rough in the other.

Cross-section of a line sawtooth

Computer-aided design systems have been developed to speed up the process of producing embossed maps and diagrams. However there is still much work to be done on the design of the maps and on methods of tactual reading.

Orientation systems
Even with an embossed map and a mobility aid, it is still very easy for a blind person to get lost. A number of electronic orientation aids have been developed, but few have been widely used because of the cost of modifying the environment.

One type of system uses infra-red transmitters mounted at street corners; the infra-red signal is modulated so that a receiver, held by the blind person, gives out an audible message. These systems can also be used to indicate the status of traffic lights. Similar radio-based systems have been used in some countries, but the advent of Bluetooth is likely to dramatically reduce the cost of installing such systems.

A different concept is for the blind person to carry a tag similar to the ones used in shop security systems. Thus machines can detect the presence of a blind person within a few metres and modify their behaviour (eg give out a speech message). The tag or smart card can be pre-coded, which could indicate that the person would prefer messages in an alternative language.

Positioning systems
Satellite navigation systems, such as the American Global Positioning System (GPS), can be used to determine one's position to a few metres. However this requires line-of-sight to three or four satellites, which means being outdoors and not close to tall buildings. This position is just given as latitude and longitude, so it needs to be integrated with a detailed digital map of the area.

Just such a system was successfully developed by the MoBIC project; this prototype system gave blind pedestrians their position within 2 metres, but only for 75% of the time. However, it proved the technical feasibility and helped identify the problems in designing the man-machine interface for blind users.

An alternative method of finding one's position is possible from mobile telephony by determining the relative signal strengths at different base stations. With the next generation of mobile systems, this has been further developed so that sighted users can be provided with information related to their locality (eg the location of the nearest cash dispenser or Chinese restaurant). The advantage of the mobile telephony system is that it does not require line of sight to satellites, but the accuracy may not be as good as GPS. But, as always, the price charged to blind people for the equipment and using the service will be a significant factor in determining its takeup.

Conclusion
Numerous wayfinding systems have been proposed, and many have been successfully developed to demonstrate the technical feasibility of the system. However what is lacking is a clear national plan for implementing systems and services so that blind users do not have to cope with different systems in each area.


Further information
Mobic Project
Personal Electronic Mobility Devices
Navigational Devices
How Can Developments in Mainstream Transport Technology Help Visually Impaired Passengers?

 



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