def down(self, point):
        self._vdown = arcball_map_to_sphere(point, self._center, self._radius)
        self._qdown = self._qpre = self._qnow
        if self._constrain and self._axes is not None:
            self._axis = arcball_nearest_axis(self._vdown, self._axes)
            self._vdown = arcball_constrain_to_axis(self._vdown, self._axis)
        else:
            self._axis = None
Returns a string that can be evaluated to a lambda function.
dataset/ETHPy150Open IEEERobotics/bot/bot/hardware/complex_hardware/transformations.py/Arcball.down--crossover with--dataset/ETHPy150Open sympy/sympy/sympy/utilities/lambdify.py/lambdastr