Tag Archives: geolocation

Google Latitude History

I thought about this service as soon as Google released the Google Latitude service : “It would be great if they could save data so that we could see where we were at a specific time.” And I very quickly published some code to get my position (you could be tracking me right now with it). I thought they would never release the history saving feature as people would have feared for their privacy and things like that. But they did it.

http://www.google.com/latitude/apps/history

I don’t know if it’s just me but I find it somehow related to what does foursquare in the way that it both help you to connect to your friends and you become rich of the location data you give them. In foursquare you have the possibility to become the mayor of nearly anything. In Google Maps, well, you possess your own tracking data.
Which basically means that the more you track, the more you create content. Couldn’t it be one of the key motivational factors ?

Google knows my mails, my contacts, my web search history, my favorites (using chrome sync), my discussions (on google talk even though I’m progressively switching to Skype), my photos, my credit card number, some friends on orkut and now my position. If you think they’re an evil big brother, you should just create better products, I’ll switch to your instantly.

Access your Google Latitude position from a .Net app

When I saw that Google Latitude now enables you to access your data by a JSON feed, I decided to make it communicate with a little GPS tracking project of mine.

I’m really found of all these ways we now have to make anything communicate with anything. You can build interfaces from any system to any other system really easily.

This code enables you to automatically get your GPS position (or the position of a friend) from your JSON Latitude feed. To be able to do that, you have to enable your KML/JSON feed.
It requires .Net 3.5’s System.Web.Extensions

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using System;
using System.Collections.Generic;
using System.Text;
using System.Web.Script.Serialization;
using System.Net;
using System.IO;
 
namespace LatitudeReader {
	class Program {
		static void Main() {
 
			Console.WriteLine( "What is your user id ?" );
 
			var userId = Console.ReadLine();
 
			if ( userId == String.Empty )
				userId = "5616045291659744796";
 
			// Url of the JSON Latitude feed
			var url = String.Format( "http://www.google.com/latitude/apps/badge/api?user={0}&type=json", userId );
 
			// We download the file
			var ms = new MemoryStream();
			Download( url, ms );
 
			// JSON in text format
			var textContent = UTF8Encoding.UTF8.GetString( ms.ToArray() );
 
			// We convert the JSON text file to an object
			// It returns 
			var jss = new JavaScriptSerializer();
			var jsonContent = jss.DeserializeObject( textContent ) as Dictionary<String, Object>;
 
			// We get the data
			var features = ( jsonContent[ "features" ] as object[] )[ 0 ] as Dictionary<string, object>;
			var geometry = features[ "geometry" ] as Dictionary<string, object>;
			var coordinates = geometry[ "coordinates" ] as object[];
			var lon = coordinates[ 0 ] as decimal?;
			var lat = coordinates[ 1 ] as decimal?;
 
			// And then the timestamp
			var properties = features[ "properties" ] as Dictionary<string, object>;
			var date = ConvertFromUnixTimestamp( (double) (int) properties[ "timeStamp" ] );
 
			// We convert the UTC date to local time
			date = date.ToLocalTime();
 
			Console.WriteLine( "{0} : {1} x {2}", date, lat, lon );
		}
 
		public static DateTime ConvertFromUnixTimestamp( double timestamp ) {
			DateTime origin = new DateTime( 1970, 1, 1, 0, 0, 0, 0 );
			return origin.AddSeconds( timestamp );
		}
 
		private const int BUFFER_SIZE = 1024;
 
		private static void Download( string url, Stream writeStream ) {
			var request = (HttpWebRequest) WebRequest.Create( url );
			var response = request.GetResponse();
 
			var readStream = response.GetResponseStream();
 
			var data = new Byte[ BUFFER_SIZE ];
 
			int n;
			do {
				n = readStream.Read( data, 0, BUFFER_SIZE );
				writeStream.Write( data, 0, n );
			} while ( n > 0 );
 
			writeStream.Flush();
			readStream.Close();
		}
	}
}

The only references you need are : System and System.Web.Extensions