Monday, February 13, 2012

[android-developers] Android linear accelerometer's values are different on several devices

I'm working on Android navigation app which uses complex of sensors to
determine position changes. In some cases device cannot achieve GPS
signal for a while (tunnel or multilevel parking) and I want to
compensate these gaps using INS approach.
Yes I know that there're another approaches like cell-id or data got
from device's carrier, but currently I'm focused on sensors.

Well, INS approach can be divided into two big tasks:
1. attitude determination (gyro or accelerometer + magnetometer or
some combination)
2. velocity and distance calculation. Here I double integrate linear
accelerometer values.

Now I try to resolve the second task. I prepared all calculation and
made contrastive analysis of data got from linear accelerometer on
different Android devices: Sensation, Motorola Xoom and Nexus S. I put
all devices on a platform and moved the platform on 8 meeters with an
acceleration on Y axis.
After that I built graphics and they really confused me - all 3
graphics has the same amplitude but peak values are different.
For example at the same moment I have 0.2 m/s^2 on Xoom and 1.2 m/s^2
on Sensation.
Hence after calculation I had a big difference in distance.

Official documentation doesn't explain it. I surfed the web but didn't
find any answer about that issue.

So my question is: did someone faced to it? Or maybe you know an
advice which will help me to solve it?

In addition, android Sensor class has few parameters. I found that
Sensation and Xoom has different RESOLUITON values -
Sensor.getResolution().
Sensation - 1.0
Xoom - 0.009576807

I'm stack with it, so any help will be really good! Thanks in advance.

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