Understanding GPS–William Bielawski, Friends of ATIA newsletter

A look at the strengths and limitations of Global Positioning Systems for pedestrians who are blind or visually impaired

A person who was totally blind once told me that she felt safe at home and at her work site, but getting from one to the other caused her anxiety. A GPS (Global Positioning System) is an orientation tool that is currently receiving a lot of attention for how it can help improve independence (and relieve anxiety) for people who are blind or visually impaired. Leader Dogs for the Blind incorporates GPS into their training and describes GPS with the acronym WWH, for Where am I? Where am I going? How do I get there? And indeed, these are the questions a GPS should answer. But how do they work? And what GPS features and limitations should you look out for?

GPS pedestrian features to know about:

Street Navigation: GPS is good at identifying street intersections and any points of interest (POI) that you pass, but they can rarely direct you to the front door of your destination. Indeed, they typically have up to a 30 foot error in knowing your exact location! Moreover, they only have data about the address and GPS location of the street intersections. Between two intersections (a street segment) they assume the addresses are distributed proportionately. So GPS calculates, for example, that 1529 West Taylor is 29% of the way between 1500 West and 1600 West (which is far from the case!) However, this error does not make GPS useless. It will still get you to the right street segment, if not to the front door. And once you do find the front door, you can save its exact location for future use.

Open Area Navigation: Another useful GPS feature is navigation to a location that is not on the street, like the door to a store in a mall. In such open areas, some GPS devices give frequent clock face directions relative to your current position and heading.  For example, “go 160 feet at 2 o’clock.” Using this can be tricky (you have to avoid obstacles), but ultimately you hone in on your destination. This feature is ideal for college quads.

Virtual Exploring: The last feature is called “virtual exploring” which simulates your movement from intersection to intersection anywhere on the map. The GPS device tells you the length of the traversed street segment. This allows you to preview an area, much like looking at a map. Some devices let you query POIs while virtually exploring.

Choosing a GPS: There are thousands of GPS apps for mobile devices. Only a few have accessible controls and give verbal directions on pedestrian routes. Sendero sells the LookAround app for the iPhone which describes upcoming intersections and nearby POIs. None of these apps support open areas or virtual exploring. A new GPS device called the Kapten Plus provides virtual exploring (without POI query), but does not handle open areas.  The Trekker Breeze does open areas beautifully, but does not allow virtual exploring. The Sendero based GPS products for Braille notetakers do it all as does the Mobile Geo app for Windows Mobile phones [however it is not yet Windows 7 compatible]. Choose the product that best meets your needs and skills.

-William Bielawski   

For the past 5 years, William Bielawski has been the manager of the Adaptive Technology Center at The Chicago Lighthouse for People who are Blind or Visually Impaired. He is currently working on a grant entitled “Freedom to Explore” which aims to improve the employability of young adults by enhancing their orientation skills with GPS. You can learn more from Bielawski by attending these upcoming ATIA webinars on computer access, mobile devices, and CCTVs.


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