Mobile Programming Pit Stop

How to use W3C Geolocation API in Mobile (Basic)

Previously Geocoding from mobile web (or ‘ordinary’ web application) is achieved through Google Gears (as pre-installed in Android 1.5+). However the W3C Geolocation API Specification has render Google Gears obsolete as newer browsers has these functionality built-in (including mobile browser).

How to include Geolocation API in a Web Page?
The most basic code that you started is listed below, the code below tests if the browser have built-in support for geolocation. If it does have geolocation support, it will call either one of the callback “successCallback” or “errorCallback”.

if (navigator.geolocation) {
  navigator.geolocation.getCurrentPosition(successCallback, errorCallback);
} else {
  error('Sorry, your browser does not support geolocation');
}

“successCallback” is call whenever the API call is successful. You need to create a function for “successCallback”, as shown in the example below:

function successCallback(pos) {
  var lat, long;

  lat = pos.coords.latitude ;
  long = pos.coords.longitude;

var element = '<p><a href="http://maps.google.com/maps?q='+lat+','+long+'&hl=en">Latitude: ' +lat+ ' Long: ' + long + '</a></p>';

alert(lat +','+long);
$('body').prepend(element);

The function will return the latitude and longitude data and stores it in ‘lat’ and ‘long’ variable, which is then displayed to the screen.

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JavaME JSR-179 Example Code : Detect Location via TinyGeocoder

I’ve completed the JSR-179 Location API code for reverse geocoding in JavaME. This code essentially is an expansion of the previous JSR-179 example that i’ve posted in the blog before, plus the Reverse-Geocoding feature, thanks to TinyGeocoder service.

What this sample MIDlet does?
It obtain coordinates via the mobile phone JSR-179 Location API and subsequently display the name of the location using TinyGeocoder reverse geocoding service.

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.location.*;
import javax.microedition.io.*;
import javax.microedition.location.*;
import java.io.*;

public class Geocoder extends MIDlet implements CommandListener
{
	public Display display;
	public Form form;
	private Command cmdExit,cmdOK;
	public StringItem si, sili;

	public Geocoder()
	{

		display =Display.getDisplay(this);
		form = new Form("Location Api test");
		cmdExit = new Command("Exit",Command.EXIT,5);
		cmdOK = new Command("OK",Command.OK,1);
		si = new StringItem("Coordinates", "Press OK");
		sili = new StringItem("Location", "");
		form.append(si);
		form.append(sili);
		form.addCommand(cmdOK);
		form.addCommand(cmdExit);
		form.setCommandListener(this);
	}

	public void startApp()
	{
		display.setCurrent(form);
	}

	public void pauseApp()
	{}

	public void destroyApp(boolean flag) {
		notifyDestroyed();
	}

	public void commandAction(Command c, Displayable d)
	{
		if (c == cmdOK){
			Retriever ret = new Retriever(this);
			ret.start();

		} else if (c == cmdExit) {
			destroyApp(false);
		}
	}

	public void displayString(String string)
	{
		si.setText(string);
	}

	public void showAlert(String message) {
		Alert alert = new Alert("Alert",message,null,AlertType.WARNING);
		display.setCurrent(alert,form);
	}

}

class Retriever extends Thread {

	private Geocoder midlet;
	Form formRunning;
	Gauge gauge;

	public Retriever(Geocoder midlet)
		{
			/**
			  * Constructor
			  *
			  * EFFECTS: Initialise the server and store midlet information
			  *
			  * @param midlet The main application midlet
			  * @param server Forecast Server URL
			  *
			  */
			this.midlet = midlet;
			formRunning = new Form("Retrieving Info");
			formRunning.append(new Gauge("Processing",false,Gauge.INDEFINITE,Gauge.CONTINUOUS_RUNNING));
			midlet.display.setCurrent(formRunning);

	}

	public void run()
		{
			/**
			* Entry point of the thread
			*
			* EFFECTS: call to connect() method
			*/
			try {
							checkLocation();
						} catch (Exception ex)
						{
							ex.printStackTrace();
							midlet.displayString(ex.toString());
			} finally {

			}

		}

	public void checkLocation() throws Exception
	{
		String string;
		Location l;
		LocationProvider lp;
		Coordinates c;
		// Set criteria for selecting a location provider:
		// accurate to 500 meters horizontally
		Criteria cr= new Criteria();
		cr.setHorizontalAccuracy(5000);
		cr.setVerticalAccuracy(5000);

		// Get an instance of the provider
		lp= LocationProvider.getInstance(cr);

		// Request the location, setting a one-minute timeout
		l = lp.getLocation(120);
		c = l.getQualifiedCoordinates();

		if(c != null ) {
		  // Use coordinate information
		  double lat = c.getLatitude();
		  double lon = c.getLongitude();
		  string = "\nLatitude : " + lat + "\nLongitude : " + lon;
		  new GetData(midlet,lat,lon).start();

		} else {
			string ="Location API failed";
		}

		formRunning.append("Obtained coordinates...");
		midlet.displayString(string);
	}
}

class GetData implements Runnable,CommandListener {

Geocoder midlet;
double lat, lon;

public GetData (Geocoder midlet, double lat, double lon) {

	this.lat = lat;
	this.lon = lon;
	this.midlet = midlet;

}

public void commandAction (Command cmd,Displayable disp)
{

}

public void start() {
       Thread t = new Thread(this);
       t.start();
}

public void run() {
	HttpConnection conn=null;
	InputStream is=null;
	String sb;

	try {
			String sUrl = "http://tinygeocoder.com/create-api.php?g="+""+lat+","+""+lon;
			conn = (HttpConnection) Connector.open(sUrl,Connector.READ);
			if (conn.getResponseCode() == HttpConnection.HTTP_OK) {
					is = conn.openInputStream();
					byte buf[] = new byte[128];
					int total =0;
					while (total < 128) {
						int count = is.read(buf,total,128-total);
						if (count<0) {
							break;
						}
						total += count;
					}

					sb = new String(buf,0,total);

				    if (sb.length() < 10) {
							midlet.showAlert("Connection error, please try again");
							is.close();
							conn.close();

							return;
					}

					  midlet.sili.setText(sb);
					//midlet.form.append(sb);
					//vectorized();
					//midlet.saveCurrency(false,midlet.vector);
					//midlet.display.setCurrent(midlet.form);
			} else if (conn.getResponseCode() == HttpConnection.HTTP_NOT_FOUND) {
					midlet.showAlert("URL not found");

			} else {
				midlet.showAlert("Server busy or unavailable. Please try again later");
			}

	} catch (SecurityException sex) {
		midlet.showAlert("Connection failed. You need to authorize this application to access network");
	} catch (IOException ioex) {
			midlet.showAlert("Connection failed. Please try again later.");
	} catch (Exception e){
		midlet.showAlert(e.toString());
		e.printStackTrace();
		//midlet.display.setCurrent(midlet.form);
	} finally {
		try {
			if (is != null) {
				is.close();
			}

			if (conn != null) {
				conn.close();
			}
		} catch (IOException ioexception) {}
			is =null;
			conn =null;
			midlet.display.setCurrent(midlet.form);

	}
}

public String URLEncode(String s)
{
		if (s!=null) {
			StringBuffer tmp = new StringBuffer();
			int i=0;
			try {
				while (true) {
					int b = (int)s.charAt(i++);
					if ((b>=0x30 && b<=0x39) || (b>=0x41 && b<=0x5A) || (b>=0x61 && b<=0x7A)) {
						tmp.append((char)b);
					}
					else {
						tmp.append("%");
						if (b <= 0xf) tmp.append("0");
						tmp.append(Integer.toHexString(b));
					}
				}
			}
			catch (Exception e) {}
			return tmp.toString();
		}
		return null;
}
}

The code requires mobile device which implements JSR-179 Location API and has been tested on Nokia E71 and 6210 Navigator.

• Download Reverse Geocoding
• Reverse Geocoding Sample Source Code