I have been away on a brief vacation.
You can measure the position with that encoder. You just cannot measure with the same resolution as the motor steps. You could do a hybrid position calculation. Read the encoder. That gives you 22.5 degrees per pulse or 11.25 degrees at each transition of the encoder output. Then add the number of steps multiplied by the 1.8 degrees per step for each step taken between encoder transitions. Just remember that the motor and the encoder will not in general be exactly synchronized, so there will be some jitter each time an encoder edge is detected.
Generally counting steps is considered adequate for position determination after homing or some other reference position is detected, the same as with incremental encoders. If your mechanical system is such that the load exceeds the torque capability of the motor, then counting steps is not valid. That is not the normal design operating mode for a stepper motor.
Lynn
