New book explains GPS for the rest of us

February 24, 2017  - By
Image: GPS World

I’ve absorbed the basics of how GPS works in the decade since I joined the staff of GPS World magazine, when I barely gave the positioning system a thought. But in those first few months, this is the book I wish I’d had.

Terms I needed to learn back then included pseudorange (nothing to do with juicy fruit), geodesy (not an undiscovered work by Homer) and multipath (not a forking trail in a park).

All of these and more are described in the new book GPS for Everyone: You Are Here by Pratap Misra. Pratap is Professor of the Practice, Department of Mechanical Engineering at Tufts University, and he sent me his new book for review. As a non-engineer, I have found it a great resource — Pratap explains complex subjects in an entertaining, highly readable narrative, accompanied by photos, illustrations and even a few cartoons.

Even if I’m not looking for a little background, I find myself engaged in the story of GPS: its history, its uses today (location-based services, defense, UAVs), privacy concerns and more.

For instance, I hadn’t given much thought to how general relativity had to be taken into account in designing the clocks for GPS satellites. If the clocks hadn’t been designed with an offset, GPS would lose 38 milliseconds a day. So much for an accurate timing reference.

Aother interesting story was the rescue of U.S. pilot Captain O’Grady, downed during the Bosnian conflict in the 1990s and quickly rescued because he was able to provide his coordinates from his handheld Flightmate GPS receiver. Today, of course, military receivers would automatically provide the location, and rescue would be even faster.

Pratap also co-authored with Per Enge of Stanford a graduate-level engineering textbook on GNSS. But for the rest of us, GPS for Everyone: You Are Here is available through bookstores everywhere.