maybeInitGroundOverlayVisibilityChangeHandlers();
groundOverlayVisibilityChangedHandlers.addHandler(handler, new BooleanCallback() {
@Override
public void callback(boolean visible) {
GroundOverlayVisibilityChangedEvent e = new GroundOverlayVisibilityChangedEvent(
GroundOverlay.this, visible);
handler.onVisibilityChanged(e);
}
});
}