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author | Mathias Agopian <mathias@google.com> | 2010-11-09 13:40:41 -0800 |
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committer | Mathias Agopian <mathias@google.com> | 2010-11-09 13:53:25 -0800 |
commit | fa33565714e4192dbab446ee1fbccb87dd414bed (patch) | |
tree | 54d6d017176beafa8687c773dc973f9b5fa848e0 /core/java | |
parent | 1b2efbca7120cf799d1242d277af354df7b0a9bb (diff) | |
download | frameworks_base-fa33565714e4192dbab446ee1fbccb87dd414bed.zip frameworks_base-fa33565714e4192dbab446ee1fbccb87dd414bed.tar.gz frameworks_base-fa33565714e4192dbab446ee1fbccb87dd414bed.tar.bz2 |
Improve gyro and accelerometer java doc
Change-Id: If055512cb51d6e3b9f2094a730bf373ca963d97d
Diffstat (limited to 'core/java')
-rw-r--r-- | core/java/android/hardware/SensorEvent.java | 56 |
1 files changed, 55 insertions, 1 deletions
diff --git a/core/java/android/hardware/SensorEvent.java b/core/java/android/hardware/SensorEvent.java index 98bf632..32ff3b3 100644 --- a/core/java/android/hardware/SensorEvent.java +++ b/core/java/android/hardware/SensorEvent.java @@ -111,6 +111,27 @@ public class SensorEvent { * This can be achieved by applying a <i>high-pass</i> filter. Conversely, a * <i>low-pass</i> filter can be used to isolate the force of gravity. * </p> + * + * <pre class="prettyprint"> + * + * public void onSensorChanged(SensorEvent event) + * { + * // alpha is calculated as t / (t + dT) + * // with t, the low-pass filter's time-constant + * // and dT, the event delivery rate + * + * final float alpha = 0.8; + * + * gravity[0] = alpha * gravity[0] + (1 - alpha) * event.data[0]; + * gravity[1] = alpha * gravity[1] + (1 - alpha) * event.data[1]; + * gravity[2] = alpha * gravity[2] + (1 - alpha) * event.data[2]; + * + * linear_acceleration[0] = event.data[0] - gravity[0]; + * linear_acceleration[1] = event.data[1] - gravity[1]; + * linear_acceleration[2] = event.data[2] - gravity[2]; + * } + * </pre> + * * <p> * <u>Examples</u>: * <ul> @@ -143,8 +164,41 @@ public class SensorEvent { * 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 + * </p> + * <p> + * values[1]: Angular speed around the y-axis + * </p> + * <p> + * values[2]: Angular speed around the z-axis + * </p> + * </ul> + * <p> + * Typically the output of the gyroscope is integrated over time to calculate + * an angle, for example: + * </p> + * <pre class="prettyprint"> + * private static final float NS2S = 1.0f / 1000000000.0f; + * private float timestamp; + * public void onSensorChanged(SensorEvent event) + * { + * if (timestamp != 0) { + * final float dT = (event.timestamp - timestamp) * NS2S; + * angle[0] += event.data[0] * dT; + * angle[1] += event.data[1] * dT; + * angle[2] += event.data[2] * dT; + * } + * timestamp = event.timestamp; + * } + * </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> + * * <h4>{@link android.hardware.Sensor#TYPE_LIGHT Sensor.TYPE_LIGHT}:</h4> - * * <ul> * <p> * values[0]: Ambient light level in SI lux units |