SensorEvent.java revision dbd77cd444f89d94ec5333223c1bc17dbe0c90cd
1/* 2 * Copyright (C) 2008 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package android.hardware; 18 19/** 20 * <p> 21 * This class represents a {@link android.hardware.Sensor Sensor} event and 22 * holds informations such as the sensor's type, the time-stamp, accuracy and of 23 * course the sensor's {@link SensorEvent#values data}. 24 * </p> 25 * 26 * <p> 27 * <u>Definition of the coordinate system used by the SensorEvent API.</u> 28 * </p> 29 * 30 * <p> 31 * The coordinate-system is defined relative to the screen of the phone in its 32 * default orientation. The axes are not swapped when the device's screen 33 * orientation changes. 34 * </p> 35 * 36 * <p> 37 * The X axis is horizontal and points to the right, the Y axis is vertical and 38 * points up and the Z axis points towards the outside of the front face of the 39 * screen. In this system, coordinates behind the screen have negative Z values. 40 * </p> 41 * 42 * <p> 43 * <center><img src="../../../images/axis_device.png" 44 * alt="Sensors coordinate-system diagram." border="0" /></center> 45 * </p> 46 * 47 * <p> 48 * <b>Note:</b> This coordinate system is different from the one used in the 49 * Android 2D APIs where the origin is in the top-left corner. 50 * </p> 51 * 52 * @see SensorManager 53 * @see SensorEvent 54 * @see Sensor 55 * 56 */ 57 58public class SensorEvent { 59 /** 60 * <p> 61 * The length and contents of the {@link #values values} array depends on 62 * which {@link android.hardware.Sensor sensor} type is being monitored (see 63 * also {@link SensorEvent} for a definition of the coordinate system used). 64 * </p> 65 * 66 * <h4>{@link android.hardware.Sensor#TYPE_ACCELEROMETER 67 * Sensor.TYPE_ACCELEROMETER}:</h4> All values are in SI units (m/s^2) 68 * 69 * <ul> 70 * <p> 71 * values[0]: Acceleration minus Gx on the x-axis 72 * </p> 73 * <p> 74 * values[1]: Acceleration minus Gy on the y-axis 75 * </p> 76 * <p> 77 * values[2]: Acceleration minus Gz on the z-axis 78 * </p> 79 * </ul> 80 * 81 * <p> 82 * A sensor of this type measures the acceleration applied to the device 83 * (<b>Ad</b>). Conceptually, it does so by measuring forces applied to the 84 * sensor itself (<b>Fs</b>) using the relation: 85 * </p> 86 * 87 * <b><center>Ad = - ∑Fs / mass</center></b> 88 * 89 * <p> 90 * In particular, the force of gravity is always influencing the measured 91 * acceleration: 92 * </p> 93 * 94 * <b><center>Ad = -g - ∑F / mass</center></b> 95 * 96 * <p> 97 * For this reason, when the device is sitting on a table (and obviously not 98 * accelerating), the accelerometer reads a magnitude of <b>g</b> = 9.81 99 * m/s^2 100 * </p> 101 * 102 * <p> 103 * Similarly, when the device is in free-fall and therefore dangerously 104 * accelerating towards to ground at 9.81 m/s^2, its accelerometer reads a 105 * magnitude of 0 m/s^2. 106 * </p> 107 * 108 * <p> 109 * It should be apparent that in order to measure the real acceleration of 110 * the device, the contribution of the force of gravity must be eliminated. 111 * This can be achieved by applying a <i>high-pass</i> filter. Conversely, a 112 * <i>low-pass</i> filter can be used to isolate the force of gravity. 113 * </p> 114 * <p> 115 * <u>Examples</u>: 116 * <ul> 117 * <li>When the device lies flat on a table and is pushed on its left side 118 * toward the right, the x acceleration value is positive.</li> 119 * 120 * <li>When the device lies flat on a table, the acceleration value is 121 * +9.81, which correspond to the acceleration of the device (0 m/s^2) minus 122 * the force of gravity (-9.81 m/s^2).</li> 123 * 124 * <li>When the device lies flat on a table and is pushed toward the sky 125 * with an acceleration of A m/s^2, the acceleration value is equal to 126 * A+9.81 which correspond to the acceleration of the device (+A m/s^2) 127 * minus the force of gravity (-9.81 m/s^2).</li> 128 * </ul> 129 * 130 * 131 * <h4>{@link android.hardware.Sensor#TYPE_MAGNETIC_FIELD 132 * Sensor.TYPE_MAGNETIC_FIELD}:</h4> 133 * All values are in micro-Tesla (uT) and measure the ambient magnetic field 134 * in the X, Y and Z axis. 135 * 136 * <h4>{@link android.hardware.Sensor#TYPE_LIGHT Sensor.TYPE_LIGHT}:</h4> 137 * 138 * <ul> 139 * <p> 140 * values[0]: Ambient light level in SI lux units 141 * </ul> 142 * 143 * <h4>{@link android.hardware.Sensor#TYPE_PROXIMITY Sensor.TYPE_PROXIMITY}: 144 * </h4> 145 * 146 * <ul> 147 * <p> 148 * values[0]: Proximity sensor distance measured in centimeters 149 * </ul> 150 * 151 * <p> 152 * <b>Note:</b> Some proximity sensors only support a binary <i>near</i> or 153 * <i>far</i> measurement. In this case, the sensor should report its 154 * {@link android.hardware.Sensor#getMaximumRange() maximum range} value in 155 * the <i>far</i> state and a lesser value in the <i>near</i> state. 156 * </p> 157 * 158 * <h4>{@link android.hardware.Sensor#TYPE_ORIENTATION 159 * Sensor.TYPE_ORIENTATION}:</h4> All values are angles in degrees. 160 * 161 * <ul> 162 * <p> 163 * values[0]: Azimuth, angle between the magnetic north direction and the 164 * y-axis, around the z-axis (0 to 359). 0=North, 90=East, 180=South, 165 * 270=West 166 * </p> 167 * 168 * <p> 169 * values[1]: Pitch, rotation around x-axis (-180 to 180), with positive 170 * values when the z-axis moves <b>toward</b> the y-axis. 171 * </p> 172 * 173 * <p> 174 * values[2]: Roll, rotation around y-axis (-90 to 90), with positive values 175 * when the x-axis moves <b>toward</b> the z-axis. 176 * </p> 177 * </ul> 178 * 179 * <p> 180 * <b>Note:</b> This definition is different from <b>yaw, pitch and roll</b> 181 * used in aviation where the X axis is along the long side of the plane 182 * (tail to nose). 183 * </p> 184 * 185 * <p> 186 * <b>Note:</b> This sensor type exists for legacy reasons, please use 187 * {@link android.hardware.SensorManager#getRotationMatrix 188 * getRotationMatrix()} in conjunction with 189 * {@link android.hardware.SensorManager#remapCoordinateSystem 190 * remapCoordinateSystem()} and 191 * {@link android.hardware.SensorManager#getOrientation getOrientation()} to 192 * compute these values instead. 193 * </p> 194 * 195 * <p> 196 * <b>Important note:</b> For historical reasons the roll angle is positive 197 * in the clockwise direction (mathematically speaking, it should be 198 * positive in the counter-clockwise direction). 199 * </p> 200 * 201 * @see SensorEvent 202 * @see GeomagneticField 203 */ 204 public final float[] values; 205 206 /** 207 * The sensor that generated this event. See 208 * {@link android.hardware.SensorManager SensorManager} for details. 209 */ 210 public Sensor sensor; 211 212 /** 213 * The accuracy of this event. See {@link android.hardware.SensorManager 214 * SensorManager} for details. 215 */ 216 public int accuracy; 217 218 219 /** 220 * The time in nanosecond at which the event happened 221 */ 222 public long timestamp; 223 224 225 SensorEvent(int size) { 226 values = new float[size]; 227 } 228} 229
