# Voxel-Based Navigation: A Systematic Review of Techniques, Applications, and Challenges
## 5 Voxel-Based Navigation
### Indoor Navigation  
The complexity and the diversity of indoor environments pose numerous challenges for indoor navigation, including intricate spatial layouts and multi-layered building structures. At the same time, the need for emergency evacuation is also critical. In such scenarios, traditional 2D maps often fail to provide sufficient information. With their detailed representation in 3D space and support for multi-story structures, voxel models have become a key tool in solving these problems. Indoor environments typically feature complex layouts, including rooms, corridors, and furniture. These complex structures require navigation systems capable of handling various spatial relationships, particularly in navigating effectively among numerous obstacles and details. Ref. [20] focuses on developing a strategy that allows drones to navigate using voxel models in known indoor environments. They designed a method to generate three-dimensional buffer zones around obstacles through an algorithm based on distance propagation, enabling drones to plot general paths that ensure safe navigation in complex indoor spaces by avoiding obstacles (see Figure 9). The rich geometric and semantic information in BIM models provides prior knowledge for indoor navigation. Ref. [88] combines \begin{table}
\begin{tabular}{l l l} \hline \hline
**Application Scenarios** & **Focus Areas** & **Example** \\ \hline \multirow{3}{*}{Indoor navigation} & Obstacle handling & [PERSON] et al. [20], [PERSON] et al. [88], [PERSON] et al. [89], [PERSON] et al. [90], \\  & Hierarchical structure recognition & [PERSON] et al. [91], [PERSON] et al. [92] \\  & [PERSON] et al. [81], [PERSON] et al. [93], [PERSON] [94], [PERSON] et al. [27] \\  & Emergency evacuation & [PERSON] et al. [32], [PERSON] et al. [95], [PERSON] et al. [96], [PERSON] et al. [97], \\  & [PERSON] et al. [98] \\ \hline \multirow{3}{*}{Outdoor navigation} & Unknown environments & [PERSON] [99], [PERSON] et al. [100], [PERSON] et al. [101], [PERSON] et al. [102], \\  & Known environments & [PERSON] et al. [103] \\ \cline{1-1}  & Autonomous driving scenarios & [PERSON] et al. [104], [PERSON] et al. [105], [PERSON] and [PERSON] [106] \\ \cline{1-1}  & & [PERSON] et al. [52], [PERSON] et al. [107], [PERSON] et al. [108], \\ \cline{1-1}  & & [PERSON] et al. [109], [PERSON] et al. [110], [PERSON] et al. [111] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Overview of voxel-based navigation from selected papers. voxel models with BIM, designing the BIM-based Indoor 3D Map model (BI3 DM) that achieves indoor routing, laying the foundation for automated indoor navigation. In indoor navigation, multi-story building structures present unique challenges. Multi-story buildings typically include vertical connections between different floors, such as stairs, elevators, and ramps, making applying traditional 2D navigation methods difficult. Ref. [27] developed a method based on octree processing of 3D indoor point clouds, generating multi-level navigation maps suitable for multi-story path planning in complex indoor environments, considering the walkable spaces necessary for floor connections. Additionally, ref. [89] simulated different movement behaviors (such as walking, rolling, and flying) in an octree-based indoor building model and integrated these behaviors into the path-planning algorithm. This method provides accurate 3D path navigation for users with different mobility needs, such as pedestrians, wheelchair users, and drones. Emergency evacuation is of paramount importance in indoor navigation. In emergencies, such as fires, earthquakes, and other critical situations, effective evacuation planning not only improves escape efficiency but also reduces the risks associated with chaos and panic. Voxel models can analyze the passability of the interior of a building, identifying the most suitable evacuation paths and avoiding congestion and hazardous areas. Ref.