You Don’t Need GPS to Track Your Location When You’re Wearing these Boots

GPS (global positioning system) location-tracking has become integral in a wide range of devices, and for good reason. GPS is remarkably reliable and accurate, and GPS sensors are small, affordable, and consume a relatively small amount of power. The major shortcoming of GPS, however, is that it requires line-of-sight to multiple satellites to work.

This sensor-equipped boot can determine position with an accuracy of about 5m, indoors or out, without GPS. (📷: Qingbo Guo/IEEE Spectrum)

That’s not possible in all situations, particularly if you’re indoors or underground. So, Darrin Young and Qingbo Guo at the University of Utah set out to build a completely untethered device for tracking a person’s location. At its core, the device is an IMU (inertial measurement unit) that attaches to a boot. Using IMUs to track movement is nothing new—that’s their whole purpose—but they’re inaccurate for long-term tracking, because small errors quickly add up.

The global positioning system can locate you within 5 to 10 meters anywhere on Earth — as long as your receiver is in the line of sight of multiple satellites. (📷: Qingbo Guo/IEEE Spectrum)

Even if you’re just standing still, an IMU by itself can easily end up drifting hundreds of feet. To overcome that tendency to drift, the team built pressure sensors into the boot for detecting steps. By only taking measurements immediately after a step was taken and then resetting the IMU, they were able to eliminate the accumulation of drift. Using that method, they could repeatably achieve an accuracy of less than 5.5 meters—even over many kilometers of walking on multiple types of terrain.