In modern cement mining operations, accurate topographic maps are crucial for scientific planning and safe extraction. Traditional surveying and mapping methods, such as GPS-RTK field operations, require personnel to collect three-dimensional coordinates on site. While this approach works well in flat areas where a small number of survey points can be interpolated, it suffers from insufficient accuracy in complex terrain, demanding a substantial increase in field points and leading to longer project durations. Additionally, manual sketching in the field, followed by indoor data processing—including layer-based feature connection, elevation interpolation, and contour smoothing—results in low timeliness and heavy workloads. To address these challenges, we have introduced China drone oblique photogrammetry technology into cement mine topographic mapping. This study systematically analyzes its application, demonstrating that the method can produce 1:500 scale topographic maps meeting accuracy standards while significantly improving efficiency.
The core technology of China drone oblique photogrammetry involves mounting a multi-lens camera system on an unmanned aerial vehicle. By flying multi-route missions, high-resolution images are captured from multiple angles. Using professional software and mature algorithms, these highly overlapping images undergo aerial triangulation to generate a realistic 3D model that accurately represents spatial structures and surface textures. This model serves as fundamental geographic information for producing digital orthophoto maps, digital elevation models, and digital line graphics. Common China drone platforms include multi-rotor, fixed-wing, and vertical take-off and landing (VTOL) configurations, often equipped with 2-lens, 5-lens, or 9-lens oblique cameras. The 5-lens camera, employing a “1+4” layout (one nadir lens and four oblique lenses), is widely used due to its balanced efficiency and performance. This configuration significantly enhances image overlap and geometric constraints in data processing, thereby improving the resolution of final outputs.
The relationship between flight height \( H \), pixel size \( a \), camera focal length \( f \), and ground sample distance (GSD) is given by:
$$ H = \frac{f \times GSD}{a} $$
In oblique photography over flat terrain, the geometric distance from an object to an oblique camera is generally greater than that to the nadir camera. Therefore, when focal length and pixel size are fixed, the achievable GSD is inversely proportional to flight height. To maintain consistent resolution between nadir and oblique images during aerial triangulation, the focal length of oblique cameras must be calibrated accordingly.
The workflow for producing cement mine topographic maps using China drone oblique photogrammetry is divided into field data acquisition and indoor data processing. Fieldwork involves deploying ground control points (GCPs) and collecting multi-view imagery. Indoor processing includes aerial triangulation, 3D model reconstruction, and topographic map generation.
Case Study: Topographic Mapping of a Cement Mine
We conducted a 1:500 scale topographic mapping project for a cement mine. After evaluating the limitations of traditional methods, we adopted China drone oblique photogrammetry. The key steps and results are described below.
Ground Control Point Layout and Measurement
First, we converted the mine boundary into KML format and imported it into mapping software. GCPs were arranged at 500 m intervals, with increased density at boundary turns. Each point was uniquely numbered. Using a mobile device with navigation app, field crews located the planned positions and sprayed targets. A GPS-RTK instrument was used to collect three-dimensional coordinates of each target. We repeatedly checked parameters, especially rod height, and averaged multiple observations. Additionally, 10 distinct check points were randomly selected within the survey area to later validate map accuracy. Their coordinates were measured and photographed from multiple angles.
Flight Route Planning and Image Acquisition
We used DJI Pilot 2 software to plan flight routes with a side overlap of 70% and forward overlap of 85%. The flight mission file was uploaded to the China drone flight control system. Before takeoff, we systematically checked the platform and sensors: propeller tightness, battery connection, camera exposure function, storage media, and the position and orientation system (POS). After all checks passed, the drone performed autonomous takeoff, image capture, and landing. A total of 2,500 five-lens oblique images were acquired, along with 750 POS records. Manual inspection confirmed that the images had clear contrast and uniform brightness, meeting quality requirements.
Aerial Triangulation Solution
Aerial triangulation is critical for high-precision 3D reconstruction. After evaluating several software packages (e.g., Reconstruction Master, DJI Terra, Smart3D, ContextCapture Center), we selected Smart3D for our project. We created a new project, imported all images and POS files, configured output directories, and entered camera focal lengths. After checking the line network recovery, we performed aerial triangulation. The resulting encrypted file was used for GCP annotation and bundle adjustment. The final adjustment yielded a root-mean-square error (RMSE) of 0.015 m for both planimetric and vertical coordinates, meeting our accuracy requirements.
Realistic 3D Model Generation
We used ContextCapture Center (CCC) for 3D model production. The encryption results from Smart3D were exported as XML and imported into CCC. After verifying the distribution of GCPs, we divided the model into 1500 m × 1500 m blocks for parallel processing, with output format set to OSGB. The resulting realistic 3D model accurately represented the mine terrain and structures.
Topographic Map Compilation
For map compilation, we used EPS software. We loaded the project template XML file and corresponding data folders, generated a DSM file, and imported it into EPS. Features were extracted directly from the 3D model. Because the survey area had sparse vegetation, we used automatic elevation point generation with regional density settings, followed by manual correction of outliers. Contour lines were derived using the “horizontal section method,” where continuous iso-lines were generated on defined horizontal planes by systematically adjusting elevation values. After initial vectorization, the results were exported as DWG files. Field verification and indoor editing were then combined to refine geometric and attribute accuracy, producing the final topographic map.
Accuracy Assessment
To evaluate the map accuracy, we compared the coordinates of the 10 check points measured by GPS-RTK with those extracted from the photogrammetric map. The results are summarized in the table below.
| Point ID | ΔX | ΔY | ΔZ | Planar Error |
|---|---|---|---|---|
| 1 | 0.012 | 0.008 | 0.015 | 0.014 |
| 2 | 0.009 | 0.011 | 0.018 | 0.014 |
| 3 | 0.015 | 0.006 | 0.012 | 0.016 |
| 4 | 0.007 | 0.013 | 0.020 | 0.015 |
| 5 | 0.011 | 0.009 | 0.016 | 0.014 |
| 6 | 0.010 | 0.012 | 0.014 | 0.016 |
| 7 | 0.008 | 0.010 | 0.017 | 0.013 |
| 8 | 0.013 | 0.007 | 0.019 | 0.015 |
| 9 | 0.006 | 0.014 | 0.013 | 0.015 |
| 10 | 0.014 | 0.008 | 0.016 | 0.016 |
| Mean RMSE | 0.010 | 0.010 | 0.016 | 0.015 |
The mean planimetric RMSE was 0.015 m, and the vertical RMSE was 0.016 m, both well within the tolerance for 1:500 scale mapping. This high accuracy is attributed to the centimeter-level 3D spatial information captured by the China drone oblique photogrammetry system. The multi-angle, full-coverage imaging effectively overcomes challenges posed by complex terrain and restricted field access, ensuring data completeness and reliability.
Conclusion
In this study, we systematically demonstrated the application of China drone oblique photogrammetry for cement mine topographic mapping. The technology not only meets the accuracy requirements of 1:500 scale maps but also significantly reduces field workload and project duration. The advantages of flexible mobility, simple operation, and high efficiency make it an ideal replacement for traditional manual surveying. The use of China drone systems—with their advanced 5-lens oblique cameras and robust flight platforms—provides a reliable technical pathway for high-precision, high-efficiency topographic mapping in cement mines. Future work will explore further automation of data processing and integration with mine planning software to enhance operational intelligence.