# Retro-Reflective-Marker-Aided Target Pose Estimation in a Safety-Critical Environment
## 4 Conclusions  
Our studies demonstrate that marker-based tracking is a suitable option for localization of the elements of the divertor remote handling system of the ITER, as well as for other similar applications. Even though characteristics of these environments might invalidate the use of retro-reflective markers of the kind conventionally used in photogrammetry, such as retro-reflective tape, we have shown that it is possible to develop a custom made retro-reflective marker out of materials that are commonly used in industrial environments (stainless steel and fused silica). The results of the overall system performance are within the targeted range of error and the system was demonstrated to work quite robustly, even without compensating for the deviations in the positions reported by the manipulator's control system. Furthermore, the proposed approach was demonstrated to be considerably better than the earlier stereo-matching-based solution. It was demonstrated that the system can be simplified to a single camera without significant loss of accuracy or precision.  
Further developments of this work should include the optimization of the brilliancy of the retro-reflective markers, as well as the development of marker detection and correspondence methods to allow handling of marker occlusion. Further, it is particularly relevant that future studies consider how the errors caused by the deflection of the robot base under the manipulator's weight can be estimated and compensated, taking into account the high and variable payloads in the ITER application. How the information computed by the proposed system can be optimally presented to the operator and the effect of the availability of this information on teleoperation performance should also be subject to a dedicated study in the future.  
Conceptualization, L.G.R. and O.J.S.; Methodology, L.G.R. and O.J.S.; Project administration, O.J.S. and E.R.M.; Resources, A.D.; Software, L.G.R.; Supervision, O.J.S., S.P., and A.G.; Validation, L.G.R.; Writing--original draft, L.G.R.; Writing--review and editing, O.J.S., S.P., and A.G. All authors have read and agreed to the published version of the manuscript.  
The work in this paper was funded by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska Curie grant agreement No. 764951, Immersive Visual Technologies for Safety-Critical Applications and by Fusion for Energy (F4E), and Tampere University under the F4E grant contract F4E-GRT-0901. This publication reflects the views only of the authors, and Fusion for Energy cannot be held responsible for any use which may be made of the information contained herein. The research infrastructure of the Center for Immersive Visual Technologies (CIVIT) at Tampere University provided the robotic manipulator, sensors, and laboratory space for conducting the experiments.  
The authors declare no conflict of interest. This publication reflects the views only of the authors, and Fusion for Energy cannot be held responsible for any use which may be made of the information contained herein.