Drawable Rotating around its center Android

I am getting strange results with the following code:

iv = (ImageView) findViewById(R.id.iv);
        iv.setImageResource(R.drawable.spinner_white_76);

        Animation a = new RotateAnimation(0.0f, 360.0f,
                Animation.RELATIVE_TO_SELF, iv.getDrawable()
                        .getIntrinsicWidth() / 2, Animation.RELATIVE_TO_SELF,
                iv.getDrawable().getIntrinsicHeight() / 2);
        a.setRepeatCount(-1);
        a.setDuration(1000);

        iv.startAnimation(a);

Whats the right way to specify the axis point (center of the drawable)?