def qrqz2xy(self, qr, qz):
"""calls the C-code in RQconv
need to deal with the special situation when the (qr, qz) is not visible on the detector
use the smallest allowable qr at the same qz instead
this is done in RQconv, with the last argument in RQconv.qrqz2xy set to 1
"""
ret = RQconv.qrqz2xy(self.data.astype(np.int32), self.exp, qr, qz, 1)
return ret.x, ret.y
