Can “overlay” size be zoomed together with the google map on android?

Question

I have been able to use "MapActivity" and "ItemizedOverlay" to draw overlays on google maps on android with Eclipse. But when the map is zooming in and out, the overlay does not change size.

I want the overlay to be "fixed" on the map, and zoom in and out along with the map. How can this be done?

I can't find the tutorial to define a boundary (e.g. with GPS coordinates as corners for the overlay image). Please provide links if you know some.

and any other ways of doing it?

Many thanks.

Answer 1

Yes, there is. I had the same issue with my application. Here's an example and it works perfectly. The circle drawn here scales as you zoom in and out of the map.

In your Overlay class:

public class ImpactOverlay extends Overlay {

private static int CIRCLERADIUS = 0;
private GeoPoint geopoint;

public ImpactOverlay(GeoPoint point, int myRadius) {
    geopoint = point;
    CIRCLERADIUS = myRadius;
}

@Override
public void draw(Canvas canvas, MapView mapView, boolean shadow) {
    // Transfrom geoposition to Point on canvas
    Projection projection = mapView.getProjection();
    Point point = new Point();
    projection.toPixels(geopoint, point);

    // the circle to mark the spot
    Paint circle = new Paint();
    circle.setColor(Color.BLACK);
    int myCircleRadius = metersToRadius(CIRCLERADIUS, mapView, (double)geopoint.getLatitudeE6()/1000000);
    canvas.drawCircle(point.x, point.y, myCircleRadius, circle);
}

public static int metersToRadius(float meters, MapView map, double latitude) {
    return (int) (map.getProjection().metersToEquatorPixels(meters) * (1/ Math.cos(Math.toRadians(latitude))));         
}
}

As your overlay re-draws from zoom, the marker will resize with it based on the metersToRadius scale. Hope it helps.

Answer 2

After a bit of looking around, I came up with the following answer (I used code from this blog to do the resizing).

I overrode the same method used above, with some differences:

• Instead of the drawCircle method I used the drawBitmap method
• I didn't use the Paint object
• I cycled over the overlay items to resize the markers

It ends up like this:

 for(OverlayItem currentPoint:mOverlays){
        geopoint =currentPoint.getPoint();
        Point point = new Point();
        projection.toPixels(geopoint, point);                       
        BitmapDrawable bitDraw= ((BitmapDrawable)currentPoint.getMarker(0));
        Drawable currentMarker = currentPoint.getMarker(0);
        /*if (currentMarker!=null){

            if (currentWidthRatio<.6f) {                
                currentWidthRatio = .6f;                    
            }
            else if (currentWidthRatio>1.5f) {
                currentWidthRatio = 1.5f;
            }
        }*/

        if (bitDraw!=null){         
        Bitmap bitmap = getResizedBitmap(bitDraw.getBitmap(),(int)(currentMarker.getIntrinsicHeight() * currentWidthRatio),
                (int)(currentMarker.getIntrinsicWidth()*currentWidthRatio));

        canvas.drawBitmap(bitmap,
                point.x - bitmap.getHeight()/2,
                point.y - bitmap.getWidth()/2, null);
        }else{
            Log.println(Log.DEBUG,"non-existent point", "");
        }
  }

Careful, though! The currentPoint.getMarker(0) method gets, as its name implies, the current marker's data. That means you have its original size, not the way it has grown (or shrunk) since. You have to have some method to:

• store the original size of the map
• verify how it has changed since (ratio)

The code I commented out handles the maximum and minimum resizing I want to allow (so the markers can be seen without overlapping / remain legible to the human eye).

I hope this helps!