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POCompensating compass lag with the gyroscope on iPhone 4
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  1. POCompensating compass lag with the gyroscope on iPhone 4
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    copied!<p>I've been experimenting with the compass and gyroscope on iPhone 4 and would like some help with an issue I'm having. I want to compensate for the slowness of the compass by using data from the gyroscope.</p> <p>Using <code>CMMotionManager</code> and its <code>CMDeviceMotion</code> object (<code>motionManager.deviceMotion</code>), I get the <code>CMAttitude</code> object. Correct me if I'm wrong (please), but here is what I've deduced from the <code>CMAttitude</code> object's <code>yaw</code> property (I don't need <code>pitch</code> nor <code>roll</code> for my purposes):</p> <ul> <li><code>yaw</code> ranges from <code>0</code> to <code>PI</code> when the phone is pointing downwards (as indicated by <code>deviceMotion.gravity.z</code>) and swinging counterclockwise and <code>0</code> to <code>-PI</code> when swung clockwise</li> <li>when the device is pointing upwards, <code>yaw</code> ranges from <code>-PI</code> to <code>0</code> and <code>PI</code> to <code>0</code>, respectively</li> <li>and from the compass data (I'm using <code>locationManager.heading.magneticHeading</code>), I see that the compass gives values from <code>0</code> to <code>360</code>, with the value increasing when swinging clockwise</li> </ul> <p>All right, so using all of this information together, I'm able to get a value I call <code>horizontal</code> that, regardless of whether the device is pointing up or down, will give values from <code>0</code> to <code>360</code> and increase when the device is swung clockwise (though I am still having trouble when <code>deviceManager.gravity.z</code> is around <code>0</code> -- the <code>yaw</code> value freaks out at this <code>gravity.z</code> value).</p> <p>It seems to me that I could "synchronize" the <code>horizontal</code> and <code>magneticHeading</code> values, using a calculated <code>horizontal</code> value that maps to <code>magneticHeading</code>, and "synchronize" the <code>horizontal</code> value to <code>magneticHeading</code> when I feel the compass has "caught up."</p> <p>So my questions: </p> <ul> <li>Am I on the right track with this? </li> <li>Am I using the gyro data from <code>CMDeviceMotion</code> properly and the assumptions I listed above correct? </li> <li>Why might <code>yaw</code> freak out when <code>gravity.z</code> is around <code>0</code>?</li> </ul> <p>Thank you very much. I look forward to hearing your answers!</p>
 

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