Create a Radius Around a Point in Google Map

Question : How do I create a 9000 meters buffer radius from a point and display placemarks that intersect that buffer.
Answer : Google Map API for android has a class that reads and draw your current location in the map.
That class is "MyLocationOverlay". The class has a "draw" method that will be called everytime user pan or zoom on the map.
So to draw a circle radius of your current location, we need to extends this class and override its draw method.

	package com.tukangandroid.tutorial;
	import android.content.Context;
	import android.graphics.Canvas;
	import android.graphics.Paint;
	import android.graphics.Point;
	import android.graphics.Paint.Style;
	import android.graphics.drawable.Drawable;
	import com.google.android.maps.GeoPoint;
	import com.google.android.maps.MapView;
	import com.google.android.maps.MyLocationOverlay;
	import com.google.android.maps.Projection;
	public class MyOwnLocationOverlay extends MyLocationOverlay{
	private MapView mapView;
	private Paint circlePainter;
	private Point screenCurrentPoint;
	private GeoPoint geoCurrentPoint;
	private int meters;
	public MyOwnLocationOverlay(Context context, MapView mapView) {
	super(context, mapView);
	this.mapView = mapView;
	}
	// This method is used to get user submitted radius from our application
	public void setMeters(int meters) {
	this.meters = meters;
	}
	@Override
	public synchronized boolean draw(Canvas canvas, MapView mapView,
	boolean shadow, long when) {
	// Set the painter to paint our circle. setColor = blue, setAlpha = 70 so the background
	// can still be seen. Feel free to change these settings
	circlePainter = new Paint();
	circlePainter.setAntiAlias(true);
	circlePainter.setStrokeWidth(2.0f);
	circlePainter.setColor(0xff6666ff);
	circlePainter.setStyle(Style.FILL_AND_STROKE);
	circlePainter.setAlpha(70);
	// Get projection from the mapView.
	Projection projection = mapView.getProjection();
	// Get current location
	geoCurrentPoint = getMyLocation();
	screenCurrentPoint = new Point();
	// Project the gps coordinate to screen coordinate
	projection.toPixels(geoCurrentPoint, screenCurrentPoint);
	int radius = metersToRadius(geoCurrentPoint.getLatitudeE6() /1000000);
	// draw the blue circle
	canvas.drawCircle(screenCurrentPoint.x, screenCurrentPoint.y, radius, circlePainter);
	return super.draw(canvas, mapView, shadow, when);
	}
	// hack to get more accurate radius, because the accuracy is changing as the location
	// getting further away from the equator
	public int metersToRadius(double latitude) {
	return (int) (mapView.getProjection().metersToEquatorPixels(meters) * (1/ Math.cos(Math.toRadians(latitude))));
	}
	}

view raw MyOwnLocationOverlay.java hosted with ❤ by GitHub

Then, we create our view, one map view, one textbox and one button

	<?xml version="1.0" encoding="utf-8"?>
	<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
	android:layout_width="fill_parent"
	android:layout_height="fill_parent"
	android:stretchColumns="1">
	<TableRow>
	<EditText
	android:id="@+id/txtRadius"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:hint="Radius"
	/>
	<Button android:id="@+id/btnSearch"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:text="Search" />
	</TableRow>
	<TableRow>
	<com.google.android.maps.MapView
	android:layout_span="2"
	android:id="@+id/mapview"
	android:layout_width="fill_parent"
	android:layout_height="fill_parent"
	android:clickable="true"
	android:apiKey="your_api_key_here"
	/>
	</TableRow>
	</TableLayout>

view raw main.xml hosted with ❤ by GitHub

After that, we need to create our main class. TukangAndroidApp.java

	package com.tukangandroid.tutorial;
	import java.util.List;
	import android.os.Bundle;
	import android.view.View;
	import android.widget.Button;
	import android.widget.TextView;
	import com.google.android.maps.GeoPoint;
	import com.google.android.maps.MapActivity;
	import com.google.android.maps.MapController;
	import com.google.android.maps.MapView;
	import com.google.android.maps.Overlay;
	public class TukangAndroidApp extends MapActivity{
	private MapView mapView;
	private List<Overlay> mapOverlays;
	private MyOwnLocationOverlay myLocationOverlay;
	private MapController mapController;
	private TextView txtRadius;
	private Button btnSearch;
	@Override
	public void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.main);
	mapView = (MapView) findViewById(R.id.mapview);
	mapView.setBuiltInZoomControls(true);
	mapController = mapView.getController();
	btnSearch = (Button) findViewById(R.id.btnSearch);
	btnSearch.setOnClickListener(new SearchListener());
	txtRadius = (TextView) findViewById(R.id.txtRadius);
	}
	private class SearchListener implements android.view.View.OnClickListener {
	@Override
	public void onClick(View v) {
	mapView.getOverlays().clear();
	mapOverlays = mapView.getOverlays();
	myLocationOverlay = new MyOwnLocationOverlay(TukangAndroidApp.this, mapView);
	myLocationOverlay.setMeters(Integer.parseInt(txtRadius.getText().toString()));
	myLocationOverlay.enableCompass();
	myLocationOverlay.enableMyLocation();
	myLocationOverlay.runOnFirstFix(new Runnable() {
	public void run() {
	mapController.animateTo(myLocationOverlay.getMyLocation());
	}
	});
	mapView.getOverlays().add(myLocationOverlay);
	displayResults();
	}
	}
	private void displayResults() {
	}
	@Override
	protected boolean isRouteDisplayed() {
	return false;
	}
	}

view raw TukangAndroidApp.java hosted with ❤ by GitHub

Dont forget to edit AndroidManifest.xml to add permissions and google map library

	<?xml version="1.0" encoding="utf-8"?>
	<manifest xmlns:android="http://schemas.android.com/apk/res/android"
	package="com.tukangandroid.tutorial"
	android:versionCode="1"
	android:versionName="1.0">
	<application android:icon="@drawable/icon" android:label="@string/app_name">
	<uses-library android:name="com.google.android.maps" />
	<activity android:name=".TukangAndroidApp"
	android:label="@string/app_name">
	<intent-filter>
	<action android:name="android.intent.action.MAIN" />
	<category android:name="android.intent.category.LAUNCHER" />
	</intent-filter>
	</activity>
	</application>
	<uses-permission android:name="android.permission.INTERNET" />
	<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
	<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
	</manifest>

view raw AndroidManifest.xml hosted with ❤ by GitHub

Run your application.
Tips : Set the GPS location from the DDMS first before you press Search, otherwise you will encounter NullPointerException
If all goes well, your application will be like this

Notice in TukangAndroidApp.java, our displayResult method didnt do anything, so we will implement the method to return some placemarks that intersect our buffer.
First, we should extends ItemizedOverlay class to create our placemark

	package com.tukangandroid.tutorial;
	import java.util.ArrayList;
	import android.graphics.drawable.Drawable;
	import com.google.android.maps.ItemizedOverlay;
	import com.google.android.maps.OverlayItem;
	public class HelloItemizedOverlay extends ItemizedOverlay<OverlayItem> {
	private ArrayList<OverlayItem> mOverlays = new ArrayList<OverlayItem>();
	public HelloItemizedOverlay(Drawable defaultMarker) {
	super(boundCenterBottom(defaultMarker));
	}
	@Override
	protected OverlayItem createItem(int i) {
	return mOverlays.get(i);
	}
	@Override
	public int size() {
	return mOverlays.size();
	}
	public void addOverlay(OverlayItem overlay) {
	mOverlays.add(overlay);
	populate();
	}
	}

view raw HelloItemizedOverlay.java hosted with ❤ by GitHub

Next, we will implement the displayResult method.
Our last TukangAndroidApp.java should look like this

	package com.tukangandroid.tutorial;
	import java.util.ArrayList;
	import java.util.List;
	import android.graphics.drawable.Drawable;
	import android.location.Location;
	import android.os.Bundle;
	import android.view.View;
	import android.widget.Button;
	import android.widget.TextView;
	import com.google.android.maps.GeoPoint;
	import com.google.android.maps.MapActivity;
	import com.google.android.maps.MapController;
	import com.google.android.maps.MapView;
	import com.google.android.maps.Overlay;
	import com.google.android.maps.OverlayItem;
	public class TukangAndroidApp extends MapActivity{
	private MapView mapView;
	private List<Overlay> mapOverlays;
	private MyOwnLocationOverlay myLocationOverlay;
	private MapController mapController;
	private TextView txtRadius;
	private Button btnSearch;
	private boolean isFound;
	@Override
	public void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.main);
	mapView = (MapView) findViewById(R.id.mapview);
	mapView.setBuiltInZoomControls(true);
	mapController = mapView.getController();
	btnSearch = (Button) findViewById(R.id.btnSearch);
	btnSearch.setOnClickListener(new SearchListener());
	txtRadius = (TextView) findViewById(R.id.txtRadius);
	}
	private class SearchListener implements android.view.View.OnClickListener {
	@Override
	public void onClick(View v) {
	mapView.getOverlays().clear();
	mapOverlays = mapView.getOverlays();
	myLocationOverlay = new MyOwnLocationOverlay(TukangAndroidApp.this, mapView);
	myLocationOverlay.setMeters(Integer.parseInt(txtRadius.getText().toString()));
	myLocationOverlay.enableCompass();
	myLocationOverlay.enableMyLocation();
	myLocationOverlay.runOnFirstFix(new Runnable() {
	public void run() {
	mapController.animateTo(myLocationOverlay.getMyLocation());
	}
	});
	mapView.getOverlays().add(myLocationOverlay);
	displayResults();
	}
	}
	private void displayResults() {
	// Create dummy list of GeoPoint
	GeoPoint point1 = new GeoPoint(35100000, 129100000);
	GeoPoint point2 = new GeoPoint(35110000, 129110000);
	GeoPoint point3 = new GeoPoint(35120000, 129120000);
	List<GeoPoint> points = new ArrayList<GeoPoint>();
	points.add(point1);
	points.add(point2);
	points.add(point3);
	mapOverlays = mapView.getOverlays();
	Drawable drawable = getResources().getDrawable(R.drawable.icon);
	HelloItemizedOverlay itemizedOverlay = new HelloItemizedOverlay(drawable);
	for(GeoPoint point : points) {
	// Create a location because Location has a distanceTo method that we can
	// use for buffering. Notice that distanceTo calculate distance in meter
	Location gpsLocation = new Location("current location");
	// Get our current gps point and use it to create a location
	GeoPoint currentLocation = myLocationOverlay.getMyLocation();
	double lat = (double) (currentLocation.getLatitudeE6() / 1000000.0);
	double lng = (double) (currentLocation.getLongitudeE6() / 1000000.0);
	gpsLocation.setLatitude(lat);
	gpsLocation.setLongitude(lng);
	Location pointLocation = new Location("point");
	pointLocation.setLatitude(point.getLatitudeE6() / 1000000.0);
	pointLocation.setLongitude(point.getLongitudeE6() / 1000000.0);
	// Calculate the distance between current location and point location
	if(gpsLocation.distanceTo(pointLocation) < Float.parseFloat(txtRadius.getText().toString())) {
	isFound = true;
	OverlayItem overlayitem = new OverlayItem(point, "", "");
	itemizedOverlay.addOverlay(overlayitem);
	}
	}
	// If any location found, draw the placemark
	if(isFound)
	mapOverlays.add(itemizedOverlay);
	}
	@Override
	protected boolean isRouteDisplayed() {
	return false;
	}
	}

view raw TukangAndroidApp.java hosted with ❤ by GitHub

Run the application, and you can see that our application will work well.

Have fun!