Practical Integration of UAV Photogrammetry and Handheld LiDAR for 3D Reconstruction in a Hillside Civil Engineering Community

Introduction:
Three-dimensional reconstruction is increasingly important in civil engineering for site documentation, terrain interpretation, facility inspection, and digital model development. However, a single data-acquisition platform often cannot simultaneously achieve broad spatial coverage and high-detail capture in complex built environments. UAV photogrammetry is efficient for roofs, slopes, and open outdoor areas, whereas handheld LiDAR is more suitable for indoor spaces and close-range structural details. This study proposes a practical integration workflow for combining these two data sources in a community-scale civil engineering survey.

Methods:
The study area was located in the Banyan Tree Community, Tongmen Village, Xiulin Township, Hualien County, Taiwan. UAV data were collected for building exteriors, roofs, and surrounding terrain, while handheld LiDAR was used for indoor spaces and near-range facade details. The workflow included mission planning, control point deployment, UAV photogrammetric reconstruction, handheld SLAM-based point-cloud generation, coordinate unification, coarse alignment, and fine registration using iterative closest point (ICP).

Results:
The integrated model successfully combined aerial coverage and ground-level detail into a more complete three-dimensional representation than either single-platform dataset. Based on 12 control/check points, the integrated point cloud achieved an average registration error of approximately ±2.8 cm and a maximum error of ±4.5 cm. The fused dataset improved geometric continuity in roof-to-facade transitions, reduced blind spots in occluded areas, and enhanced the practical usability of the model for civil engineering survey and documentation tasks.

Conclusions:
The results demonstrate that integrating UAV photogrammetry and handheld LiDAR is an effective and operationally feasible approach for 3D reconstruction in mixed indoor-outdoor civil environments. The proposed workflow improves completeness, registration quality, and engineering applicability, and is suitable for poster presentation as an applied civil engineering case study.