Surveying of Inaccessible Topographical Area at Remote Location by UAV

Abstract

Surveying remote and inaccessible terrains using conventional methods is difficult due to terrain complexity, safety risks, time consumption, and high costs. This study demonstrates the use of an Unmanned Aerial Vehicle (UAV) for efficient and accurate topographical surveying. A multirotor UAV equipped with a high-resolution camera and GNSS module was used to capture aerial images following a planned grid pattern with 75% forward and 65% lateral overlap. Ground Control Points (GCPs) were established using RTK GNSS for accurate georeferencing. The collected images were processed using Open Drone Map (ODM) to generate orthophotos, Digital Elevation Models (DEM), and 3D point clouds, which were further analyzed in QGIS. Results showed a Ground Sample Distance (GSD) of 3.2 cm/pixel, horizontal accuracy of 0.032 m, and vertical accuracy of 0.048 m. Compared to traditional methods, UAV surveying reduced field time from 3–5 days to under 4 hours and significantly lowered costs. This study confirms that UAV-based surveying is a reliable, cost-effective, and efficient solution for mapping inaccessible terrain.

Introduction

The text explains a UAV-based topographical surveying system as an alternative to traditional ground surveying methods for mapping difficult or hazardous terrain.

Core idea

Conventional surveying methods like total stations and GNSS are accurate but require physical access to all survey points, making them slow, expensive, and unsafe in inaccessible areas such as forests, hills, and flood-prone regions. UAVs (drones) provide a modern solution by enabling aerial data collection and efficient terrain mapping.

Limitations of traditional methods

• Require manual access to all locations
• Time-consuming and labor-intensive
• Unsafe in hazardous terrain
• Produce low-density (point-based) data
• High operational cost

UAV-based solution

UAVs improve surveying by:

• Capturing high-resolution aerial images
• Generating dense 3D terrain models
• Reducing cost, time, and safety risks
• Providing better coverage of inaccessible areas

Methodology

The study uses a structured UAV workflow:

• UAV system: quadcopter with 12 MP camera and GNSS module
• Flight planning: 80 m altitude, high image overlap, grid flight path
• Ground Control Points (GCPs): 12 RTK-measured points for accuracy (9 for processing, 3 for validation)
• Data collection: automated flights under stable weather conditions
• Processing: OpenDroneMap (ODM) used for feature detection, image matching, 3D point cloud generation, DEM, and orthophoto creation
• GIS analysis: QGIS used for contour maps, slope, hillshade, and volume estimation

Key findings from literature

• UAV photogrammetry can achieve very high accuracy (<5 cm)
• Structure-from-Motion (SfM) enables detailed 3D reconstruction
• At least 5–6 GCPs are needed for reliable accuracy
• High image overlap (>60%) is essential
• UAV surveys are faster, safer, and often comparable to LiDAR

Conclusion

The project successfully demonstrated UAV-based topographical surveying. The method provides: • High accuracy • Fast data collection • Low cost • High safety UAV surveying is a practical alternative to conventional methods, especially in inaccessible areas.

References

[1] Neitzel & Klonowski (2011) [2] Colomina & Molina (2014) [3] Westoby et al. (2012) [4] Hugenholtz et al. (2013) [5] Agüera-Vega et al. (2017) [6] Open Drone Map (2015–2024) [7] DGCA Drone Rules (2021)

Copyright

Copyright © 2026 Banoth Praveen, Banothu Rakesh, Sriram Nikhil, Mr. B. Narsimha, Mr. M. Harish Kumar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.