xref: /frameworks/base/core/java/android/hardware/SensorEvent.java

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.hardware;

/**
 * <p>
 * This class represents a {@link android.hardware.Sensor Sensor} event and
 * holds informations such as the sensor's type, the time-stamp, accuracy and of
 * course the sensor's {@link SensorEvent#values data}.
 * </p>
 *
 * <p>
 * <u>Definition of the coordinate system used by the SensorEvent API.</u>
 * </p>
 *
 * <p>
 * The coordinate-system is defined relative to the screen of the phone in its
 * default orientation. The axes are not swapped when the device's screen
 * orientation changes.
 * </p>
 *
 * <p>
 * The X axis is horizontal and points to the right, the Y axis is vertical and
 * points up and the Z axis points towards the outside of the front face of the
 * screen. In this system, coordinates behind the screen have negative Z values.
 * </p>
 *
 * <p>
 * <center><img src="../../../images/axis_device.png"
 * alt="Sensors coordinate-system diagram." border="0" /></center>
 * </p>
 *
 * <p>
 * <b>Note:</b> This coordinate system is different from the one used in the
 * Android 2D APIs where the origin is in the top-left corner.
 * </p>
 *
 * @see SensorManager
 * @see SensorEvent
 * @see Sensor
 *
 */

public class SensorEvent {
    /**
     * <p>
     * The length and contents of the {@link #values values} array depends on
     * which {@link android.hardware.Sensor sensor} type is being monitored (see
     * also {@link SensorEvent} for a definition of the coordinate system used).
     * </p>
     *
     * <h4>{@link android.hardware.Sensor#TYPE_ACCELEROMETER
     * Sensor.TYPE_ACCELEROMETER}:</h4> All values are in SI units (m/s^2)
     *
     * <ul>
     * <p>
     * values[0]: Acceleration minus Gx on the x-axis
     * </p>
     * <p>
     * values[1]: Acceleration minus Gy on the y-axis
     * </p>
     * <p>
     * values[2]: Acceleration minus Gz on the z-axis
     * </p>
     * </ul>
     *
     * <p>
     * A sensor of this type measures the acceleration applied to the device
     * (<b>Ad</b>). Conceptually, it does so by measuring forces applied to the
     * sensor itself (<b>Fs</b>) using the relation:
     * </p>
     *
     * <b><center>Ad = - �Fs / mass</center></b>
     *
     * <p>
     * In particular, the force of gravity is always influencing the measured
     * acceleration:
     * </p>
     *
     * <b><center>Ad = -g - �F / mass</center></b>
     *
     * <p>
     * For this reason, when the device is sitting on a table (and obviously not
     * accelerating), the accelerometer reads a magnitude of <b>g</b> = 9.81
     * m/s^2
     * </p>
     *
     * <p>
     * Similarly, when the device is in free-fall and therefore dangerously
     * accelerating towards to ground at 9.81 m/s^2, its accelerometer reads a
     * magnitude of 0 m/s^2.
     * </p>
     *
     * <p>
     * It should be apparent that in order to measure the real acceleration of
     * the device, the contribution of the force of gravity must be eliminated.
     * 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>
     * <p>
     * <u>Examples</u>:
     * <ul>
     * <li>When the device lies flat on a table and is pushed on its left side
     * toward the right, the x acceleration value is positive.</li>
     *
     * <li>When the device lies flat on a table, the acceleration value is
     * +9.81, which correspond to the acceleration of the device (0 m/s^2) minus
     * the force of gravity (-9.81 m/s^2).</li>
     *
     * <li>When the device lies flat on a table and is pushed toward the sky
     * with an acceleration of A m/s^2, the acceleration value is equal to
     * A+9.81 which correspond to the acceleration of the device (+A m/s^2)
     * minus the force of gravity (-9.81 m/s^2).</li>
     * </ul>
     *
     *
     * <h4>{@link android.hardware.Sensor#TYPE_MAGNETIC_FIELD
     * Sensor.TYPE_MAGNETIC_FIELD}:</h4>
     * 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_LIGHT Sensor.TYPE_LIGHT}:</h4>
     *
     * <ul>
     * <p>
     * values[0]: Ambient light level in SI lux units
     * </ul>
     *
     * <h4>{@link android.hardware.Sensor#TYPE_PROXIMITY Sensor.TYPE_PROXIMITY}:
     * </h4>
     *
     * <ul>
     * <p>
     * values[0]: Proximity sensor distance measured in centimeters
     * </ul>
     *
     * <p>
     * <b>Note:</b> Some proximity sensors only support a binary <i>near</i> or
     * <i>far</i> measurement. In this case, the sensor should report its
     * {@link android.hardware.Sensor#getMaximumRange() maximum range} value in
     * the <i>far</i> state and a lesser value in the <i>near</i> state.
     * </p>
     *
     * <h4>{@link android.hardware.Sensor#TYPE_ORIENTATION
     * Sensor.TYPE_ORIENTATION}:</h4> All values are angles in degrees.
     *
     * <ul>
     * <p>
     * values[0]: Azimuth, angle between the magnetic north direction and the
     * y-axis, around the z-axis (0 to 359). 0=North, 90=East, 180=South,
     * 270=West
     * </p>
     *
     * <p>
     * values[1]: Pitch, rotation around x-axis (-180 to 180), with positive
     * values when the z-axis moves <b>toward</b> the y-axis.
     * </p>
     *
     * <p>
     * values[2]: Roll, rotation around y-axis (-90 to 90), with positive values
     * when the x-axis moves <b>toward</b> the z-axis.
     * </p>
     * </ul>
     *
     * <p>
     * <b>Note:</b> This definition is different from <b>yaw, pitch and roll</b>
     * used in aviation where the X axis is along the long side of the plane
     * (tail to nose).
     * </p>
     *
     * <p>
     * <b>Note:</b> This sensor type exists for legacy reasons, please use
     * {@link android.hardware.SensorManager#getRotationMatrix
     * getRotationMatrix()} in conjunction with
     * {@link android.hardware.SensorManager#remapCoordinateSystem
     * remapCoordinateSystem()} and
     * {@link android.hardware.SensorManager#getOrientation getOrientation()} to
     * compute these values instead.
     * </p>
     *
     * <p>
     * <b>Important note:</b> For historical reasons the roll angle is positive
     * in the clockwise direction (mathematically speaking, it should be
     * positive in the counter-clockwise direction).
     * </p>
     *
     * @see SensorEvent
     * @see GeomagneticField
     */
    public final float[] values;

    /**
     * The sensor that generated this event. See
     * {@link android.hardware.SensorManager SensorManager} for details.
     */
   public Sensor sensor;

    /**
     * The accuracy of this event. See {@link android.hardware.SensorManager
     * SensorManager} for details.
     */
    public int accuracy;


    /**
     * The time in nanosecond at which the event happened
     */
    public long timestamp;


    SensorEvent(int size) {
        values = new float[size];
    }
}