'NOTE: This cannot be called until after this has been added
to an Axes, otherwise unit conversion will fail. This
maxes it very important to call the accessor method and
not directly access the transformation member variable.'

def _recompute_transform(self):

    assert (self._patch_type == u'circle')
    center = (self.convert_xunits(self._center[0]), self.convert_yunits(self._center[1]))
    width = self.convert_xunits(self._width)
    height = self.convert_yunits(self._height)
    self._patch_transform = mtransforms.Affine2D().scale((width * 0.5), (height * 0.5)).rotate_deg(self._angle).translate(*center)
