def find_backward(self, s):
        return self.total_text.rfind(s, 0, self.start)
take tilted ellipse geometry and get Xr,Yr,Rr in ring coordinates
dataset/ETHPy150Open zoofIO/flexx/translate_to_legacy.py/Token.find_backward--crossover with--dataset/ETHPy150Open mkenworthy/exorings/exorings.py/sky_to_ring