Efficient Map Overlays in Android Google Map

Question

I want to do the following and am kind of stuck on these for a few days:

1. I was trying to draw polylines (I have encoded polylines, but have managed to decode those) that move when I move the map.
   The only solution that I found was for Geopoints to be transformed into screen coordinates... which won't move if I move the map.

2. I used HelloItemizedOverlay to add about 150 markers and it gets very very slow.
   Any idea what to do? I was thinking about threads (handler).

3. I was looking for some sort of a timer function that executes a given function periodically, say, every 1 minute or so.

4. I was also looking for ways to clear the Google map from all the markers/lines, etc.

Answer 1

Answers given below :

1) Here's a solution that I used :

/** Called when the activity is first created. */
private List<Overlay> mapOverlays;

private Projection projection;  

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    linearLayout = (LinearLayout) findViewById(R.id.zoomview);
    mapView = (MapView) findViewById(R.id.mapview);
    mapView.setBuiltInZoomControls(true);

    mapOverlays = mapView.getOverlays();        
    projection = mapView.getProjection();
    mapOverlays.add(new MyOverlay());        

}

@Override
protected boolean isRouteDisplayed() {
    return false;
}

class MyOverlay extends Overlay{

    public MyOverlay(){

    }   

    public void draw(Canvas canvas, MapView mapv, boolean shadow){
        super.draw(canvas, mapv, shadow);

    Paint   mPaint = new Paint();
        mPaint.setDither(true);
        mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(2);

        GeoPoint gP1 = new GeoPoint(19240000,-99120000);
        GeoPoint gP2 = new GeoPoint(37423157, -122085008);

        Point p1 = new Point();
        Point p2 = new Point();

    Path    path = new Path();

    Projection  projection.toPixels(gP1, p1);
        projection.toPixels(gP2, p2);

        path.moveTo(p2.x, p2.y);
        path.lineTo(p1.x,p1.y);

        canvas.drawPath(path, mPaint);
    }

courtesy: Drawing a line/path on Google Maps

2) Here's what worked for me :

createMarkers()
{ 
    for(elem:bigList)
    { 
        GeoPoint geoPoint = new GeoPoint((int)(elem.getLat()*1000000), (int) (elem.getLon()*1000000)); 
        OverlayItem overlayItem = new OverlayItem(geoPoint, elem.getName(), elem.getData()); 
        itemizedOverlay.addOverlay(overlayItem); 
    } 

    itemizedOverlay.populateNow(); 
    mapOverlays.add(itemizedOverlay); //outside of for loop 
} 

and in MyOverlay:

public void addOverlay(OverlayItem overlay) 
{ 
    m_overlays.add(overlay); 
} 

public void populateNow()
{
    populate(); 
}

courtesy: stackoverflow.com unknown link

3) The best way is to use a timer class. A very detailed description of the timer class and how to use it is given at this link :

http://life.csu.edu.au/java-tut/essential/threads/timer.html

4) I used this code :

if(!mapOverlays.isEmpty()) 
{ 
    mapOverlays.clear(); 
    mapView.invalidate(); 
} 

Hope these answers help atleast one other person. Thanks.

Answer 2

I have the same problem. We are developing an iphone app and an android app at the same time. I have 2500 + map overlays. No problem on iphone; a huge performance hit on android when calling populate() after adding all overlays. (Of course, my first try was to call populate() every time after adding an overlay; a typical mistake due to google's tutorial. Now I am calling populate() just once, after all 2500+ overlays have been added to the ItemizedOverlay.)

So the single populate() call takes over 40 seconds to complete on an htc hero device. I had to put in a busy indicator; no progress bar is possible because we cannot get any information about the progress of populate().

I tried another solution: not use ItemizedOverlay but add overlays by hand, subclassing Overlay. Result: indeed it is much faster to add all those overlays to the map; however, the map becomes unusable due to constant calling of the draw() method on each overlay. In my draw method, I tried to optimize as much as possible; I do not create a bitmap every time. My draw() method looks like this:

public void draw(android.graphics.Canvas canvas, MapView mapView, boolean shadow)  {
// our marker bitmap already includes shadow.
// centerPoint is the geopoint where we need to put the marker.
 if (!shadow) {
  Point point = new Point();  
  mapView.getProjection().toPixels(centerPoint, point);
  canvas.drawBitmap(markerBitmap, point.x, point.y, null);
 }

}

Here markerBitmap is precomputed. I don't know what else I could optimize. Is there some kind of populate() call required if we are not using ItemizedOverlay??? I could not find any good answers for that.

Right now I resort to caching the ItemizedOverlay once it has been created in a background thread. This way at least the user does not have to wait every time.

Answer 3

For #2, I don't think you solved anything there. Your hard-to-read code is showing how to put markers on overlay and then, how to add that overlay to the map. That's exactly how I do it. I have map with around 300 hotels and it takes around 5 seconds for Android on my Nexus One to create markers. The whole thing is running inside thread and I guess I will have to do some sort of progress bar to let user know what's going on.

I am working on app that already exists on iPhone and it seems iPhone doesn't have any issues to almost instantaneously draw these 300+ markers. I'll have hard time to explain existence of progress bar to my bosses.

If anybody have idea how to optimize this process... I will be grateful.

Here is my code:

    ...
        for (int m = 0; m < ArrList.size(); m++) {
            tName = ArrList.get(m).get("name").toString();
            tId = ArrList.get(m).get("id").toString();
            tLat = ArrList.get(m).get("lat").toString();;
            tLng = ArrList.get(m).get("lng").toString();;
            try {
                lat = Double.parseDouble(tLat);
                lng = Double.parseDouble(tLng);
                p1 = new GeoPoint(
                        (int) (lat * 1E6), 
                        (int) (lng * 1E6));
                OverlayItem overlayitem = new OverlayItem(p1, tName, tId);
                itemizedoverlay.addOverlay(overlayitem);
            } catch (NumberFormatException e) {
                Log.d(TAG, "NumberFormatException" + e);    
            }
        } 

I know I could save some time by avoiding this String > Double conversion, but I don't feel that would give me significant saving.. or it would?

Answer 4

For your 4th question.... simply use the mapOverlays.clear(); method and all the previous markers will be vanished.

code:

if(!mapOverlays.isEmpty()) { 
    mapOverlays.clear();
    mapView.invalidate();
}

Answer 5

Multiple number of drawable objects can be added to a single Overlay which can then be added to the map. Hence, drawing x number of overlay's for x number of objects wouldnt be necessary unless the objects are of different types. Code snippet.. .. Here, CustomPinPoint is my class which extends ItemizedOverlay<OverlayItem>

CustomPinPoint customPinPoint = new CustomPinPoint(drawable, Main.this);

OverlayItem tempOverLayItem = new OverlayItem(
    touchedPoint, "PinPoint", "PintPoint 2"); //Point One
customPinPoint.insertPinPoint(tempOverLayItem);
tempOverLayItem = new OverlayItem(new GeoPoint(
        (int)(-27.34498 * 1E6), (int)(153.00724 * 1E6)), "PinPoint",
    "PintPoint 2"); //Point Two
customPinPoint.insertPinPoint(tempOverLayItem);
overlayList.add(customPinPoint); //Overlay added only once