iPhone Geolocation Bookmarklets

Very few websites have implemented the new javascript GPS geolocation features that were intruduced with HTML 5. However, there are a few sites that use latitude and longitude directly in their URLs.

I first wanted a quick way to get my current latitude and longitude while looking at Heavens Above. It’s a great site that allows you to find visible satellites based upon your current location. Here’s the bookmarklet that I created:

javascript:navigator.geolocation.getCurrentPosition(function(g){c=g.coords;z=c.altitude;z=z?z:0;d=new Date(2009,0,1,0,0,0,0).toLocaleString().substr(-3,3);window.location="http://www.heavens-above.com/?lat="+c.latitude+"&lng="+c.longitude+"&alt="+z+"&loc=iPhone&tz="+d;},function(){alert("Permission denied.")});

Copy this to your bookmarks, and then when accessed on an iPhone, it will directly load the site with your current location entered!

I had to jump through several hoops here. When the altitude is not available (when only using cell-tower triangulation), the javascript code returns null. The website only supports numeric values, so z=z?z:0 replaces the null with a 0. Secondly, the website needs the local timezone, but unfortunately it only accepts a small subset of the three letter codes (and not the numeric offset from UTC). Even worse, the daylight savings version of the code (EDT/CDT/MDT/PDT) are unsupported – the site just assumes that you follow the trend (sorry Arizona). So I grab the code from January 1, 2009 (when daylight savings is not in effect), and parse the three letter code from that string.

For most sites, you’d only need something of the form (The NOAA’s weather forecast, for example):

javascript:navigator.geolocation.getCurrentPosition(function(g){c=g.coords;window.location="http://forecast.weather.gov/MapClick.php?lat="+c.latitude+"&lon="+c.longitude;},function(){alert("Permission denied.")});

Now if only I could find a way to save the javascript bookmark to the Home Screen, I’d be set!

Posted by Matt on Aug 06, 2009