Conservation-oriented comparison of non-contact robotic survey systems for immovable cultural heritage in constrained environments

Non-contact survey of immovable cultural heritage in complex and constrained environments faces challenges from limited accessibility, structural occlusion, GNSS denial, fragile materials, and strict deployment requirements. This review synthesizes evidence on aerial robots, ground mobile robots, special-purpose systems, including cable-driven robots and manipulators, and heterogeneous collaborative systems. Existing studies remain fragmented across individual platforms, algorithms, and application scenarios, limiting conservation-oriented cross-platform comparison. Through systematic literature screening, evidence-role classification, cross-platform coding, and technology-readiness assessment, platforms are evaluated in terms of conservation safety, task effectiveness, and deployment maturity. Results show that suitability depends on material sensitivity, spatial configuration, survey requirements, and deployment conditions. Current research emphasizes localization, path planning, and control, while giving less attention to embodiment and deployment design, despite their importance for accessibility, observation effectiveness, and field deployability. Accordingly, a design-first paradigm is proposed, integrating platform selection, embodiment design, low-disturbance deployment, and field validation for heritage-oriented robotics.