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Trying Out Indoor Navigation Using Inertial Sensing

IEEE Spectrum tests a sensor-laden smartphone that maps where GPS can’t

3 min read
Our reporter finds her way around the Museum of Contemporary Art, in Taipei, using a prototype smartphone that can navigate without GPS.
Photo: Bill Chen

21 November 2012—At no point did the kung-fu masters in Ang Lee’s film Crouching Tiger, Hidden Dragon need a navigation system to locate targets. As a kung-fu film fan with a bad sense of direction, however, I was happy to have an experimental new indoor navigation system guide me through the exhibition “King Hu: The Renaissance Man,” at the Museum of Contemporary Art in Taipei last August. ( Hu’s 1971 film, A Touch of Zen, was one of the inspirations for Crouching Tiger, Hidden Dragon.)

As anyone who’s ever been lost in a multistory shopping center or parking garage knows, GPS doesn’t work indoors. So Internet giants like Google, telecom operators, and smartphone makers are working on indoor navigation.

I came to the Hu exhibition to try out a version of indoor navigation that calculates your position by a form of inertial sensing, or dead reckoning—reconstructing your position from acceleration and orientation. At the entrance, where GPS signals vanished to almost none, I was given a Google Nexus One smartphone that had been modified by engineers from STMicroelectronics and CSR. The phone’s software displayed my location on a map of the ground floor. As I moved, the app displayed my route and showed me as a little cartoon-person icon, whose motions simultaneously mimicked mine as I walked, rested, and even climbed stairs.

The modified smartphone contained an STMicroelectronics-CSR indoor navigation module, a combination of CSR’s navigation software, SiRFusion, and an STMicroelectronics MEMS chip that featured accelerometers, gyroscopes, a compass, and a pressure sensor. Sam Sun, a CSR field-applications engineering manager, opened the back of the smartphone to show me the module and its smaller-than-a-square-centimeter MEMS chip. They fit into the Nexus One in a space that was freed up by replacing the original battery with a smaller one.

When I finished climbing the stairs and stepped onto the second floor, the smartphone showed me a new map. Even if a GPS signal had been available, figuring out what floor I was on would’ve been a challenge. GPS is only one-third as accurate in the vertical direction as it is in the horizontal—too fuzzy to tell one floor from another. The key here was the pressure sensor—the only type of sensor the modified Nexus One contained that you don’t commonly find in today’s portables. Although we can’t feel the decrease in air pressure from one floor to another, several companies have developed sensors that can. “So if you go to a skyscraper offering location-based services, say, the Taipei 101 building, the device can tell you which floor you’re actually on by measuring levels of the air pressure,” says Robert Yu, an STMicroelectronics senior technical marketing and application manager.

The software was customized with information on the museum’s show. Whenever I approached an object, its icon would pop up on the display, which I could click on to hear a description of it. The experience was much better than using a headset listening device to follow a self-guided audio tour, because I didn’t have to spend seconds matching the object’s number with the audio segment.

“What if two icons are shown at the same time, partly overlapped?” I asked CSR’s Sun, when we approached an object that was just dozens of centimeters away from another.“How do I know which is which?”

“Don’t forget, you still have eyes,” he replied, adding that the navigation system could be switched to manual mode if users preferred retrieving the information for specific targets.

So even without a well-trained kung-fu master’s sense of direction, I could still easily navigate the museum’s collection of King Hu’s kung-fu films.

For more advances in indoor navigation, see “Navigating the Great Indoors,” IEEE Spectrum, November 2012.

About the Author

Yu-Tzu Chiu is a Taipei correspondent for Bloomberg BNA. She has chronicled Taiwan’s tech policies for IEEE Spectrum since 2000. In April 2012, she reported for us on how Taiwan’s tech hubs were taking advantage of the 2011 Japanese earthquake and the Thai floods.


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