The present application is directed to a medical instrument system, comprising: an elongate instrument； a first optical sensor coupled to the elongate instrument； a second optical sensor coupled to the elongate instrument in a known geometric relationship to the first optical sensor； and a controller operatively coupled to the first and second optical sensors and configured to conduct an error analysis by comparing signals received from the first and second optical sensors. Further, the present application is directed to a corresponding method for determining shape and/or position data of an elongate instrument, comprising: coupling a first optical sensor to the elongate instrument； coupling a second optical sensor to the elongate instrument in a known geometric relationship to the first optical sensor； coupling the first and second optical sensors to a controller； and conducting, using the controller, an error analysis by comparing signals received from the first and second optical sensors.
