Sensors CS 4720 Mobile Application Development CS 4720 Sensor - - PowerPoint PPT Presentation

CS 4720

Sensors

CS 4720 – Mobile Application Development

CS 4720

Sensor Categories

• Android sensors as separated into one of three

broad categories:

– Motion sensors – measure force and rotation – Environmental sensors – measure parameters such as illumination air temperature and pressure – Position sensors – measure physical positioning of the device

2

CS 4720

Hardware vs. Software

• Although it might be natural to think of all

sensors as hardware, that isn’t the case

• A sensor in the case of Android is any

component that provides information about the outside world

• So, some “sensors” are actually software

components that take data from hardware sensors to generate different kinds of data

• These are called “virtual sensors”

3

CS 4720

Sensors? What sensors?

• Sensors aren’t guaranteed!
• There is no Android spec for required sensors!
• So, you have to check for the sensor first
• Android registers sensors into particular

categories defined by a global final variable

• You can ask for the default sensor of any

category to get the currently active one (yes, you can have more than one!)

• Also, different capabilities and drivers!

4

CS 4720

Getting Data

• Sensors work somewhat similarly to a service
• In a sense, they are always running in the

background

• You can allocate a sensor event listener to

monitor a sensor for changes to:

– Data – Availability – Precision / Resolution – Power Consumption

5

CS 4720

SensorEventListener

• To access the data from a sensor, you need a

SensorEventListener

• You can implement this class from your Activity
• Inside onCreate, you can ask the sensor service

to provide the current default sensor for any given category

6

CS 4720

SensorEvent

• At regular intervals, a sensor reports a

SensorEvent to all registered listeners

• A SensorEvent has an array associated with it

called values

• For each sensor, the data in each slot in the

array represents different data

7

CS 4720

SensorEvent - Accelerometer

• values[0] – acceleration force on x axis
• values[1] – acceleration force on y axis
• values[2] – acceleration force on z axis

8

CS 4720

Difficulty of Using Analog Data

• How do you read “user intent”?
• Did they mean to do something, or did they

drop the device?

• How could “shake to shuffle” mess things up

for runners?

• Also, it’s a LOT of data coming really fast!
• How do you not overwhelm your program?

9

CS 4720

Advanced Sensors

• Location
• Camera
• Microphone / Audio

10

CS 4720

Location Services

• Location services come in two flavors:

– The location service that directly provides the GPS coordinate information – Google Maps API

11

CS 4720

Location Services

• Location services is by far the easier of the two

methods to get a simple location

• Works similarly to other sensors
• See old example code for this!

12

CS 4720

Google Play Services

• Google Play Services encompass all of the

potential cloud features that Google provides through their Play store

• Has to be manually added into your manifest

so it can be compiled into your app

• API keys might be required for a given service

so that Google can track usage (and charge as needed)

13

CS 4720

Some Google Play Services

• Google+
• Google Account Login
• Google Analytics
• Google Messaging
• Google Drive
• Google Maps
• Google Ads
• Google Play Game services

14

CS 4720

Connecting to Google Play Services

• To utilize many of these, you instantiate an

instance of the GoogleApiClient class in your app

• When instantiated, you connect to a particular

service

• You then override

– onConnected() – onConnectionSuspended() – onConnectionFailed()

15

CS 4720

Authorization

• In some cases, your app needs to be

authorized in some way before it can access the service

• For instance, in order to do good public/private

key authentication for Google Sign-In, your app needs to have an API key digitally signed by a hash of your signing certificate

16

CS 4720

Camera

• Two ways to get an image

– Send an intent to the default camera program – Write your own camera

17

CS 4720

Sending an Intent (aka Easy Way)

// create Intent to take a picture and return control to the // calling application Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE); // create a file to save the image fileUri = getOutputMediaFileUri(MEDIA_TYPE_IMAGE); // set the image file name intent.putExtra(MediaStore.EXTRA_OUTPUT, fileUri); // start the image capture Intent startActivityForResult(intent,CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE);

Also works for video!

18

CS 4720

Writing a Camera (aka Hard Way)

• Verify there IS a camera
• Use the Camera class
• Create a CameraPreview class to show what

the Camera sees (the viewfinder)

• Add all buttons necessary to zoom, capture,

etc.

• Write code to grab current pixel set and write

to file

• Let’s not talk about video…

19

CS 4720

Microphone / Audio

• Actually, a bit different

mRecorder = new MediaRecorder(); mRecorder.setAudioSource(MediaRecorder.AudioSource.MIC); mRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP); mRecorder.setOutputFile(mFileName); mRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB); try { mRecorder.prepare(); } catch (IOException e) { Log.e(LOG_TAG, "prepare() failed"); } mRecorder.start(); 20

CS 4720

CoreMotion and CoreLocation

• First, let’s do the “how to do these”
• CoreMotion controls access to the

accelerometer and gyroscope

• CoreLocation controls access to the GPS

21

CS 4720

CoreLocation

22 func createLocationManager(startImmediately startImmediately: Bool){ locationManager = CLLocationManager() if let manager = locationManager{ print("Successfully created the location manager") manager.delegate = self if startImmediately{ manager.startUpdatingLocation() } } }

CS 4720

CoreLocation

23 func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) { if locations.count == 0{ //handle error here return } let newLocation = locations[0] print("Latitude = \(newLocation.coordinate.latitude)") print("Longitude = \(newLocation.coordinate.longitude)") lat.text = String(newLocation.coordinate.latitude) lon.text = String(newLocation.coordinate.longitude) }

CS 4720

CoreLocation

24 /* Are location services available on this device? */ if CLLocationManager.locationServicesEnabled(){ /* Do we have authorization to access location services? */ switch CLLocationManager.authorizationStatus(){ case .AuthorizedAlways: /* Yes, always */ createLocationManager(startImmediately: true) case .AuthorizedWhenInUse: /* Yes, only when our app is in use */ createLocationManager(startImmediately: true) case .Denied: /* No */ displayAlertWithTitle("Not Determined", message: "Location services are not allowed for this app")

CS 4720

CoreMotion - Shake

25 // function to allow for detecting a shake

• verride func motionEnded(motion: UIEventSubtype,

withEvent event: UIEvent?) { if motion == .MotionShake{ let controller = UIAlertController(title: "Shake", message: "The device is shaken", preferredStyle: .Alert) controller.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil)) presentViewController(controller, animated: true, completion: nil) } }

CS 4720

CoreMotion - Accelerometer

26 @IBAction func startAccel(sender: UIButton) { if motionManager.accelerometerAvailable{ let queue = NSOperationQueue() motionManager.startAccelerometerUpdatesToQueue(queue, withHandler: {data, error in guard let data = data else{ return } print("X = \(data.acceleration.x)") print("Y = \(data.acceleration.y)") print("Z = \(data.acceleration.z)")} ) } else { print("Accelerometer is not available") } }