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improve the gyroscope javadoc

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change the sample code to something more useful and more
correct.

Change-Id: Ia81f86a2f409edbb395405ababae307663824cb9
This commit is contained in:
Mathias Agopian
2011-09-07 15:56:03 -07:00
parent 7a57009c3a
commit ad7f33a29c
1 changed files with 55 additions and 22 deletions
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77
core/java/android/hardware/SensorEvent.java
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@ -154,16 +154,16 @@ public class SensorEvent {
* All values are in micro-Tesla (uT) and measure the ambient magnetic field
* in the X, Y and Z axis.
*
* <h4>{@link android.hardware.Sensor#TYPE_GYROSCOPE Sensor.TYPE_GYROSCOPE}:</h4>
* All values are in radians/second and measure the rate of rotation
* around the X, Y and Z axis. The coordinate system is the same as is
* used for the acceleration sensor. Rotation is positive in the counter-clockwise
* direction. That is, an observer looking from some positive location on the x, y.
* or z axis at a device positioned on the origin would report positive rotation
* if the device appeared to be rotating counter clockwise. Note that this is the
* standard mathematical definition of positive rotation and does not agree with the
* definition of roll given earlier.
*
* <h4>{@link android.hardware.Sensor#TYPE_GYROSCOPE Sensor.TYPE_GYROSCOPE}:
* </h4> All values are in radians/second and measure the rate of rotation
* around the device's local X, Y and Z axis. The coordinate system is the
* same as is used for the acceleration sensor. Rotation is positive in the
* counter-clockwise direction. That is, an observer looking from some
* positive location on the x, y or z axis at a device positioned on the
* origin would report positive rotation if the device appeared to be
* rotating counter clockwise. Note that this is the standard mathematical
* definition of positive rotation and does not agree with the definition of
* roll given earlier.
* <ul>
* <p>
* values[0]: Angular speed around the x-axis
@ -176,28 +176,61 @@ public class SensorEvent {
* </p>
* </ul>
* <p>
* Typically the output of the gyroscope is integrated over time to calculate
* an angle, for example:
* Typically the output of the gyroscope is integrated over time to
* calculate a rotation describing the change of angles over the timestep,
* for example:
* </p>
*
* <pre class="prettyprint">
* private static final float NS2S = 1.0f / 1000000000.0f;
* private final float[] deltaRotationVector = new float[4]();
* private float timestamp;
* public void onSensorChanged(SensorEvent event)
* {
*
* public void onSensorChanged(SensorEvent event) {
* // This timestep's delta rotation to be multiplied by the current rotation
* // after computing it from the gyro sample data.
* if (timestamp != 0) {
* final float dT = (event.timestamp - timestamp) * NS2S;
* angle[0] += event.values[0] * dT;
* angle[1] += event.values[1] * dT;
* angle[2] += event.values[2] * dT;
* // Axis of the rotation sample, not normalized yet.
* float axisX = event.values[0];
* float axisY = event.values[1];
* float axisZ = event.values[2];
*
* // Calculate the angular speed of the sample
* float omegaMagnitude = sqrt(axisX*axisX + axisY*axisY + axisZ*axisZ);
*
* // Normalize the rotation vector if it's big enough to get the axis
* if (omegaMagnitude > EPSILON) {
* axisX /= omegaMagnitude;
* axisY /= omegaMagnitude;
* axisZ /= omegaMagnitude;
* }
*
* // Integrate around this axis with the angular speed by the timestep
* // in order to get a delta rotation from this sample over the timestep
* // We will convert this axis-angle representation of the delta rotation
* // into a quaternion before turning it into the rotation matrix.
* float thetaOverTwo = omegaMagnitude * dT / 2.0f;
* float sinThetaOverTwo = sin(thetaOverTwo);
* float cosThetaOverTwo = cos(thetaOverTwo);
* deltaRotationVector[0] = sinThetaOverTwo * axisX;
* deltaRotationVector[1] = sinThetaOverTwo * axisY;
* deltaRotationVector[2] = sinThetaOverTwo * axisZ;
* deltaRotationVector[3] = cosThetaOverTwo;
* }
* timestamp = event.timestamp;
* float[] deltaRotationMatrix = new float[9];
* SensorManager.getRotationMatrixFromVector(deltaRotationMatrix, deltaRotationVector);
* // User code should concatenate the delta rotation we computed with the current rotation
* // in order to get the updated rotation.
* // rotationCurrent = rotationCurrent * deltaRotationMatrix;
* }
* </pre>
*
* <p>In practice, the gyroscope noise and offset will introduce some errors which need
* to be compensated for. This is usually done using the information from other
* sensors, but is beyond the scope of this document.</p>
*
* <p>
* In practice, the gyroscope noise and offset will introduce some errors
* which need to be compensated for. This is usually done using the
* information from other sensors, but is beyond the scope of this document.
* </p>
* <h4>{@link android.hardware.Sensor#TYPE_LIGHT Sensor.TYPE_LIGHT}:</h4>
* <ul>
* <p>