Sensors 9
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The document discusses different types of sensors available on smartphones and how to access sensor data on iOS and Android platforms. It covers motion sensors like accelerometers and gyroscopes, environmental sensors like temperature and pressure sensors, and position sensors like magnetometers. It provides code examples of accessing the accelerometer sensor and using filters to isolate the force of gravity on iOS and Android. It also explains how to use the Android sensor framework to determine available sensors and get sensor events.
![LOW PASS FILTER APPLIED
public void onSensorChanged(SensorEvent event){
// In this example, alpha is calculated as t / (t + dT),
// where t is the low-pass filter's time-constant and
// dT is the event delivery rate.
final float alpha = 0.8;
// Isolate the force of gravity with the low-pass filter.
gravity[0] = alpha * gravity[0] + (1 - alpha) * event.values[0];
gravity[1] = alpha * gravity[1] + (1 - alpha) * event.values[1];
gravity[2] = alpha * gravity[2] + (1 - alpha) * event.values[2];
// Remove the gravity contribution with the high-pass filter.
linear_acceleration[0] = event.values[0] - gravity[0];
linear_acceleration[1] = event.values[1] - gravity[1];
linear_acceleration[2] = event.values[2] - gravity[2];
}](https://image.slidesharecdn.com/ycw7pjjlqgydiav4x7zh-signature-55e8d63eea27c6fc2d1657acf7cc783e72e866b220d2e16aeb4912c683ae8ee7-poli-150719231810-lva1-app6892/85/Sensors-9-34-320.jpg)
Sensors 9
- 1. SENSORS CPE 490/590 – Smartphone Development by: Michael T. Shrove
- 2. IOS
- 3. CMMOTIONMANAGER • A CMMotionManager object is the gateway to the motion services provided by iOS. • These services provide an app with accelerometer data, rotation-rate data, magnetometer data, and other device-motion data such as attitude. • These types of data originate with a device’s accelerometers and (on some models) its magnetometer and gyroscope.
- 4. TYPES OF MOTION SENSORS • Accelerometer • Gyroscope • Magnetometer • Device Motion (Combines all three)
- 14. ANDROID
- 15. OVERVIEW • Android Sensors Overview • Types of Sensors • Motion Sensors • Environmental Sensors • Position Sensors • Introduction to Sensor Framework
- 16. SENSORS OVERVIEW • Most Android-powered devices have built-in sensors that measure motion, orientation, and various environmental conditions. • These sensors are capable of providing raw data with high precision and accuracy, and are useful if you want to monitor three-dimensional device movement or positioning, or you want to monitor changes in the ambient environment near a device.
- 17. SENSOR EXAMPLES • For example, a game might track readings from a device's gravity sensor to infer complex user gestures and motions, such as tilt, shake, rotation, or swing. • Likewise, a weather application might use a device's temperature sensor and humidity sensor to calculate and report the dewpoint, or a travel application might use the geomagnetic field sensor and accelerometer to report a compass bearing.
- 18. TYPES OF SENSORS • Motion Sensors • Environmental Sensors • Position Sensors
- 19. MOTION SENSORS • These sensors measure acceleration forces and rotational forces along three axes. • This category includes accelerometers, gravity sensors, gyroscopes, and rotational vector sensors.
- 20. ENVIRONMENT SENSORS • These sensors measure various environmental parameters, such as ambient air temperature and pressure, illumination, and humidity. • This category includes barometers, photometers, and thermometers.
- 21. POSITION SENSORS • These sensors measure the physical position of a device. • This category includes orientation sensors and magnetometers.
- 22. SENSORS • You can access sensors available on the device and acquire raw sensor data by using the Android sensor framework. • For example, you can use the sensor framework to do the following: • Determine which sensors are available on a device. • Determine an individual sensor's capabilities, such as its maximum range, manufacturer, power requirements, and resolution. • Acquire raw sensor data and define the minimum rate at which you acquire sensor data. • Register and unregister sensor event listeners that monitor sensor changes.
- 23. INTRODUCTION TO SENSOR FRAMEWORK • The Android sensor framework lets you access many types of sensors. Some of these sensors are hardware-based and some are software-based. • Hardware-based sensors are physical components built into a handset or tablet device. They derive their data by directly measuring specific environmental properties, such as acceleration, geomagnetic field strength, or angular change. • Software-based sensors are not physical devices, although they mimic hardware-based sensors. Software-based sensors derive their data from one or more of the hardware-based sensors and are sometimes called virtual sensors or synthetic sensors. • The linear acceleration sensor and the gravity sensor are examples of software-based sensors.
- 24. SENSOR MANAGER • You can use this class to create an instance of the sensor service. • This class provides various methods for accessing and listing sensors, registering and unregistering sensor event listeners, and acquiring orientation information. • This class also provides several sensor constants that are used to report sensor accuracy, set data acquisition rates, and calibrate sensors.
- 25. SENSOR • You can use this class to create an instance of a specific sensor. • This class provides various methods that let you determine a sensor's capabilities.
- 26. SENSOR EVENT • The system uses this class to create a sensor event object, which provides information about a sensor event. • A sensor event object includes the following information: • the raw sensor data • the type of sensor that generated the event • the accuracy of the data • the timestamp for the event.
- 27. SENSOR EVENTLISTENER • You can use this interface to create two callback methods that receive notifications (sensor events)z; • sensor values change • sensor accuracy changes.
- 28. DEVICES • Few Android-powered devices have every type of sensor. • For example, most handset devices and tablets have an accelerometer and a magnetometer, but fewer devices have barometers or thermometers. • Also, a device can have more than one sensor of a given type. • For example, a device can have two gravity sensors, each one having a different range.
- 29. MOTION SENSORS • The Android platform provides several sensors that let you monitor the motion of a device. • Two of these sensors are always hardware-based (the accelerometer and gyroscope), and three of these sensors can be either hardware-based or software- based (the gravity, linear acceleration, and rotation vector sensors).
- 30. MOTION SENSORS • Accelerometer • Gravity • Gyroscope • Linear acceleration • Rotation Vector • http://developer.android.com/ guide/topics/sensors/sensors _motion.html
- 31. USING THE ACCELEROMETER • An acceleration sensor measures the acceleration applied to the device, including the force of gravity. • The following code shows you how to get an instance of the default acceleration sensor: private SensorManager mSensorManager; private Sensor mSensor; ... mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE); mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
- 32. ACCELEROMETER++ • Conceptually, an acceleration sensor determines the acceleration that is applied to a device (Ad) by measuring the forces that are applied to the sensor itself (Fs) using the following relationship: • Ad = - ∑Fs / mass • However, the force of gravity is always influencing the measured acceleration according to the following relationship: • Ad = -g - ∑F / mass
- 33. ACCELEROMETER += 1 • For this reason, when the device is sitting on a table (and not accelerating), the accelerometer reads a magnitude of g = 9.81 m/s2. • Similarly, when the device is in free fall and therefore rapidly accelerating toward the ground at 9.81 m/s2, its accelerometer reads a magnitude of g = 0 m/s2. • Therefore, to measure the real acceleration of the device, the contribution of the force of gravity must be removed from the accelerometer data. • This can be achieved by applying a high-pass filter. • Conversely, a low-pass filter can be used to isolate the force of gravity.
- 34. LOW PASS FILTER APPLIED public void onSensorChanged(SensorEvent event){ // In this example, alpha is calculated as t / (t + dT), // where t is the low-pass filter's time-constant and // dT is the event delivery rate. final float alpha = 0.8; // Isolate the force of gravity with the low-pass filter. gravity[0] = alpha * gravity[0] + (1 - alpha) * event.values[0]; gravity[1] = alpha * gravity[1] + (1 - alpha) * event.values[1]; gravity[2] = alpha * gravity[2] + (1 - alpha) * event.values[2]; // Remove the gravity contribution with the high-pass filter. linear_acceleration[0] = event.values[0] - gravity[0]; linear_acceleration[1] = event.values[1] - gravity[1]; linear_acceleration[2] = event.values[2] - gravity[2]; }
- 35. ENVIRONMENTAL SENSORS • The Android platform provides four sensors that let you monitor various environmental properties. • You can use these sensors to monitor relative ambient humidity, illuminance, ambient pressure, and ambient temperature near an Android-powered device. • All four environment sensors are hardware-based and are available only if a device manufacturer has built them into a device. With the exception of the light sensor, which most device manufacturers use to control screen brightness, environment sensors are not always available on devices. • Because of this, it's particularly important that you verify at runtime whether an environment sensor exists before you attempt to acquire data from it
- 36. ENVIRONMENTAL SENSORS • Ambient Temperature • Light • Pressure • Relative Humidity • Temperature • http://developer.android.com/ guide/topics/sensors/sensors _environment.html
- 37. HOW DOES ENVIRONMENTAL SENSORS DIFFER? • Unlike most motion sensors and position sensors, which return a multi-dimensional array of sensor values for each SensorEvent, environment sensors return a single sensor value for each data event. • For example, the temperature in °C or the pressure in hPa. • Also, unlike motion sensors and position sensors, which often require high-pass or low-pass filtering, environment sensors do not typically require any data filtering or data processing.
- 38. POSITION SENSORS • The Android platform provides two sensors that let you determine the position of a device: the geomagnetic field sensor and the orientation sensor. • The Android platform also provides a sensor that lets you determine how close the face of a device is to an object (known as the proximity sensor). • The geomagnetic field sensor and the proximity sensor are hardware- based. • Most handset and tablet manufacturers include a geomagnetic field sensor. • Likewise, handset manufacturers usually include a proximity sensor to determine when a handset is being held close to a user's face (for example, during a phone call). • The orientation sensor is software-based and derives its data from the accelerometer and the geomagnetic field sensor.
- 39. POSITION SENSORS • Magnetic Field • Orientation • Proximity • http://developer.android. com/guide/topics/sensor s/sensors_position.html
- 40. POSITION SENSORS++ • Position sensors are useful for determining a device's physical position in the world's frame of reference. • For example, you can use the geomagnetic field sensor in combination with the accelerometer to determine a device's position relative to the magnetic North Pole. • You can also use the orientation sensor (or similar sensor-based orientation methods) to determine a device's position in your application's frame of reference. • Position sensors are not typically used to monitor device movement or motion, such as shake, tilt, or thrust
- 41. EXAMPLES
- 43. GET A LIST OF ALL SENSORS
- 44. GET DEFAULT SENSOR FOR THE TYPE
- 45. MONITORING SENSOR EVENTS To monitor raw sensor data you need to implement two callback methods that are exposed through the SensorEventListener interface: • onAccuracyChanged() • onSensorChanged()
- 46. MONITOR SENSOR EVENTS • A sensor's accuracy changes • In this case the system invokes the onAccuracyChanged() method, providing you with a reference to the Sensor object that changed and the new accuracy of the sensor. • A sensor reports a new value • In this case the system invokes the onSensorChanged() method, providing you with a SensorEvent object. A SensorEvent object contains information about the new sensor data, including: the accuracy of the data, the sensor that generated the data, the timestamp at which the data was generated, and the new data that the sensor recorded.
- 47. EXAMPLE
- 48. QUESTIONS????