An apparatus for measuring a deformation distribution of an object having a longitudinal dimension comprises a structure for supporting the object. A sensor unit comprises a base, a contact member having a body connected to the base by a rotational joint such rotational degrees of freedom are provided between the base and the contact member, an end of the body configured to contact and move along the object, and at least one sensor for determining an orientation of the body relative to the base. A displacement module enables relative movement between the sensor unit and the structure for the sensor unit to relatively move along the object in the longitudinal dimension. A method and system for measuring a rigidity distribution of an object having a longitudinal dimension are also provided.