Active3D: Active High-Fidelity 3D Reconstruction via Hierarchical Uncertainty Quantification

We present an active exploration framework for high-fidelity 3D reconstruction that incrementally builds a multi-level uncertainty space and selects next-best-views through an uncertainty-driven motion planner. We introduce a hybrid implicit-explicit representation that fuses neural fields with Gaussian primitives to jointly capture global structural priors and locally observed details. Based on this hybrid state, we derive a hierarchical uncertainty volume that quantifies both implicit global structure quality and explicit local sur- face confidence. To focus optimization on the most infor- mative regions, we propose an uncertainty-driven keyframe selection strategy that anchors high-entropy viewpoints as sparse attention nodes, coupled with a viewpoint-space slid- ing window for uncertainty-aware local refinement. The plan- ning module formulates next-best-view selection as an Ex- pected Hybrid Information Gain problem and incorporates a risk-sensitive path planner to ensure efficient and safe ex- ploration.