Monday, November 16, 2009

Cross Browser Geolocation

You might have heard that Joe Hewitt has given Apple the finger, and is moving on (or more accurately moving back to) mobile web development. You can do a lot on mobile web browsers -- more than you can do on desktop browsers. This can seem counterintuitive at first. However, flavors of WebKit have a huge share of mobile web use, and it supports a lot of features that you can't count on in the IE-dominated world of desktop browsers. One of those coveted features is geolocation. However, geolocation support is far from standardized even among the high end WebKit based browsers.

Geolocation on Mobile Safari is nice, or more accurately it is "standardized." It follows the W3C standard. All you have to do is access the navigator.geolocation object. Here is a super simple example:
var gps = navigator.geolocation;
    if (gps){
        gps.getCurrentPosition(successHandler);
    } 
}

function successHandler(position){
  var lat = position.coords.latitude;
  var long = position.coords.longitude;
  doSomethingUseful(lat, long);
}
Pretty easy, huh? This will work on Mobile Safari running on iPhone OS 3+. As mentioned, it is standard. It will also work on newer versions of Firefox, which presumably includes Mobile Firefox, a.k.a. Fennec. However, that is the limit of the portability of this code. It will not work in Android's browser.
Android's flavor of WebKit, does not support the standard. However, it does support geolocation via Google Gears. That's right, instead of supporting the open standard, it implements the same feature using a proprietary technology. Shocking, I know. So if you are going to run JS that should access geolocation on both the iPhone and one of the zillion Android phones out there, you will need to include the gears_init.js bootstrap file. Then you can re-write the above like this:
function load(){
    var gps = navigator.geolocation;
    if (gps){
        gps.getCurrentPosition(successHandler);
    } else {
        if (window.google && google.gears){
            gps = google.gears.factory.create('beta.geolocation');
            gps.getCurrentPosition(function (position){
               successHandler({coords : position});
            }) ;
        }
    }
}

function successHandler(position){
  var lat = position.coords.latitude;
  var long = position.coords.longitude;
  doSomethingUseful(lat, long);
}
So this is pretty close to the standard, but not quite. The Gears variant also supports the getCurrentPosition API. However, the object that it passes to the success function is different. It is a flatter structure. So in the above example, we wrap it inside another object so that we can reuse the same handler.
I haven't tried the webOS browser, yet or the Nokia WebKit variant yet. Here's hoping they are close to the standard used by Safari.

4 comments:

Anonymous said...

I think Nokia and Palm don't implement a geolocation api yet. Blackberry has its own api "blackberry.location".

Anonymous said...

I understand that geolocation using browser api is hard to standardize.

Maybe they can consider using the XML based server side query like IP geolocation.

For example, http://www.fraudlabs.com/ip2location.aspx

Tony said...

I've run into a problem with geolocation on android 2.0.1 - hoped you'd take a look at the writeup on Stack Overflow.

Thanks either way, this post was interesting and informative to me.

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