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.