Any modern mobile phone is equipped with accelerometer and compass sensor. Many techniques is developed to use the ease of phone sensors for indoor tracking. Using accelerometer to estimate the walking distance, using compass to detect heading direction.
- Accelerometer: how we use accelerometer sensor to estimate walking distance
- Compass: how we use compass sensor to detect direction
We did use accelerometer to calculate distance by double integral acceleration w.r.t time. However, the phone sensor is inaccurate and produce noise, therefore, this approach results a high distance error. In our experiment walking for 25m, most of the case, the distance is estimated around a haft of 25m.
Then, we tried another approach by using accelerometer to detect walking steps. If we have number of walking steps, we can multiply it with average step length to get distance. That is also a constraint because each person will have a different step length. So the error in this approach highly depends on step length. We detect walking step by examining the y-value in acceleration. In our experiment, the y-value when walking has a recognizable pattern. So by using this value, we can detect walking steps.
The picture below represents 3-axis acceleration value when walking. Notice the y-value pattern.
Walking pattern on 3-axis acceleration
To use compass, it’s quite easier then use accelerometer to calculate distance. All we need is to extract the azimuth value from compass, then do some trivial mathematical transformation to get actual direction.
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