Figure 4: Architecture of the proposed localization system architecture. The robot scrolling along the riser generates a set of kinematic variables that is measured by the IMU. The accelerations are transformed to the global reference system, using IMU attitude outputs, and considered as the inputs of the KF. To compensate the drift caused by integrated sensor noise, the KF fuses the IMU with depth sensor data, that is, an absolute measurement. Before entering in the KF, the external measurements are processed by the method described in Section 6, using IMU attitude data.