Can I use Javascript to get the compass heading for iOS and Android?

Question

Can I use Javascript in a cross-platform way to get the compass heading in iOS and Android (with Chrome), without using something like PhoneGap? I know iOS has DeviceOrienta

Answer 1

Yes you can! Unfortunately the alpha doesn't work on iPhones/iPads. With Mobile Safari, alpha is based on the direction the device was pointing when device orientation was first requested. The included webkit offers you the compass heading. To make it work for all other browsers (which all supports alpha as compassheading) you can use the following Javascript code:

if (window.DeviceOrientationEvent) {
  // Listen for the deviceorientation event and handle the raw data
  window.addEventListener('deviceorientation', function(eventData) {
    var compassdir;

    if(event.webkitCompassHeading) {
      // Apple works only with this, alpha doesn't work
      compassdir = event.webkitCompassHeading;  
    }
    else compassdir = event.alpha;
  });
}

Android also supports Webkit, so would also use event.webkitCompassHeading, but that's OK.

BTW: "oncompassneedscalibration" is also not supported for iPhones and iPads.

Answer 2

As a primer you should review this previous related StackOverflow answer and be familiar with the general practical considerations for using DeviceOrientation Events in web applications.

The simple solution I provided in my previous related StackOverflow answer only applies to browsers that implement absolute deviceorientation events (i.e. browsers where the deviceorientation alpha property is compass-oriented). That means the solution provided there currently only works in Android browsers and not iOS-based browsers or any other browser that does not provide absolute-based deviceorientation event data.

To reliably obtain the current compass heading across both Android and iOS browsers today you need to handle both absolute and non-absolute implementations that provide the additional webkitCompassHeading property and make sure to account for any current screen orientation changes as part of that. AFAIK the only library that currently does this is Full Tilt JS (disclaimer: I am the author of this library).

The following code will give you the same correct compass heading across both iOS and Android browsers, taking account of the differences in device orientation implementations and applying any necessary runtime screen orientation transforms too:

<!-- Include the Full Tilt JS library from https://github.com/richtr/Full-Tilt-JS -->
<script src="fulltilt-min.js"></script>

<script>

  // Obtain a new *world-oriented* Full Tilt JS DeviceOrientation Promise
  var promise = FULLTILT.getDeviceOrientation({ 'type': 'world' });

  // Wait for Promise result
  promise.then(function(deviceOrientation) { // Device Orientation Events are supported

    // Register a callback to run every time a new 
    // deviceorientation event is fired by the browser.
    deviceOrientation.listen(function() {

      // Get the current *screen-adjusted* device orientation angles
      var currentOrientation = deviceOrientation.getScreenAdjustedEuler();

      // Calculate the current compass heading that the user is 'looking at' (in degrees)
      var compassHeading = 360 - currentOrientation.alpha;

      // Do something with `compassHeading` here...

    });

  }).catch(function(errorMessage) { // Device Orientation Events are not supported

    console.log(errorMessage);

    // Implement some fallback controls here...

  });

</script>

Here is a demo that demonstrates this technique to obtain the compass heading the user is facing. It should work well on both iOS and Android browsers.

The implementation of the code in that demo is as shown above and can be viewed on Github at ./scripts/compass.js:L268-L272.

Answer 3

I believe you can use the "heading" field of the location object, from navigator.geolocation, please see here:

https://developer.mozilla.org/en-US/docs/WebAPI/Using_geolocation

I know no other way.

Hope it helps, A.