title: Why three (redundant?) accelerometer variations in android sensors
body: <p>In android, we have Sensor.TYPE_GRAVITY, Sensor.TYPE_ACCELEROMETER, Sensor.TYPE_LINEAR_ACCELERATION.</p>
  
  <p>And it is known from android developer forum that,
  "The output of the accelerometer, gravity and linear-acceleration sensors must obey the following relation:
  acceleration = gravity + linear-acceleration"</p>
  
  <p>Do Sensor.TYPE_GRAVITY and Sensor.TYPE_LINEAR_ACCELERATION make use of the same sensor as Sensor.TYPE_ACCELEROMETER - i.e., the accelerometer?
  What is purpose of having 3 different constants if the value of one can be deduced using the other using low pass and high pass filters? </p>