_rect = _mainImageDisplay.getVisibleArea();
Point2D.Double p = new Point2D.Double(_rect.getX(), _rect.getY());
Point2D.Double d = new Point2D.Double(_rect.getWidth(), _rect.getHeight());
CoordinateConverter cc = _imageDisplay.getCoordinateConverter();
cc.userToScreenCoords(p, false);
cc.userToScreenCoords(d, true);
_rect.setRect(p.getX(), p.getY(), d.getX(), d.getY());
}
/**
* Update the rect object with the coordinates of the visible area