-(UIImage *)addCircle:(UIImage *)img radius:(CGFloat)radius latCon:(CGFloat)lat lonCon:(CGFloat)lon{

    int w = img.size.width;

    int h = img.size.height; 

    lon = h - lon;

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);

//draw the circle

CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);

CGRect leftOval = {lat- radius/2, lon - radius/2, radius, radius};

CGContextSetRGBFillColor(context, 0.0, 0.0, 1.0, 0.3);

CGContextAddEllipseInRect(context, leftOval);

CGContextFillPath(context);

    CGImageRef imageMasked = CGBitmapContextCreateImage(context);

    CGContextRelease(context);

    CGColorSpaceRelease(colorSpace);

    return [UIImage imageWithCGImage:imageMasked];

}