Friday, April 06, 2012

5 Cool Things you can do with HTML5 (p3)

Location, location, location, it's all about location...


Probably one of the most frequently used HTML5 features is geoLocation. Why? Because it is very easy to use and cool too!
You can check the corresponding example page on http://apex.oracle.com/pls/apex/f?p=22115:GEOLOCATION.
So how does that work?
In fact it is just a few lines of code. First include the Google Javascript API (<script type="text/javascript" src="http://maps.googleapis.com/maps/api/js?sensor=false"></script>).
The next step (on Page Load) is to actually get the current position of the browser device by
if (navigator.geolocation) {
  navigator.geolocation.getCurrentPosition(showLocation, handleError);
} else {
  error('GeoLocation is not supported in this browser');
}
Where  showLocation specifies the callback method that retrieves the location information. This method is called asynchronously with an object corresponding to the Position object which stores the returned location information. So you can use this function to actually draw the map and place the marker. And ErrorHandler is an optional parameter that specifies the callback method that is invoked when an error occurs in processing the asynchronous call. This method is called with the PositionError object that stores the returned error information. So when somethings goes wrong you can show an alert with your own message.
Depending on the security settings of the browser, your user might see a message like "apex.oracle.com wants to track your physical location". The user has to accept or deny access to this information. In the privacy settings of your browser you can see what sites have access to your location.

And for actually determining your position, Google uses either your IP-address - so that might be quite inadequate when you use proxies - or the GPS in your (mobile) device. For the latter type of device you can also use navigator.geolocation.watchPosition(showLocation, handleError);. Then that function will be called every time the Geo of your device changes. So you can draw a map of where the user of your app has been during the period the app is active (like Runkeeper does).

You can see the full W3C API description here.
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