Comparative Accuracy Assessment of UAV-Derived Orthophoto, DSM, and DTM Generated with and without Ground Control Points: A Case Study of the LMTC Premises, Nepal
Aug 2026· Journal of Land Management and Geomatics Education· Vol 8, pp. 50-60· 0 citations
Abstract
Unmanned Aerial Vehicle (UAV) photogrammetry is increasingly used for local-scale mapping because it enables rapid generation of high-resolution orthophotos and elevation products. However, the positional and vertical quality of these products depends strongly on the georeferencing strategy, particularly the use of Ground Control Points (GCPs). This study evaluates the effect of GCPs on the accuracy of UAV-derived orthophoto, Digital Surface Model (DSM), and Digital Terrain Model (DTM) at the premises of the Land Management Training Center (LMTC), Dhulikhel, Nepal. The same UAV image block of 334 images was processed under two workflows: one using only onboard image geolocation and another using five surveyed GCPs. Eight independent checkpoints were used for accuracy assessment. Orthophoto planimetric accuracy was evaluated using checkpoint coordinates, while vertical agreement of DSM and DTM was assessed using surveyed ground elevations. In addition, pairwise checkpoint-distance analysis and supplementary object-based comparison were used to examine relative geometric differences in the orthophotos. The with-GCP orthophoto achieved a horizontal RMSEH of 0.063 m, whereas the without-GCP orthophoto showed an RMSEH of 3.507 m. Similarly, the with-GCP DSM and DTM achieved RMSEZ values of 0.131 m and 0.143 m, respectively, compared with 15.385 m and 15.347 m in the without-GCP workflow. The without-GCP orthophoto also exhibited systematic westward and northward displacement and minor scale-related geometric differences. The results demonstrate that GCP-based processing remains essential for reliable campus-scale UAV photogrammetry when the outputs are intended for measurement, terrain representation, planning, and other applications requiring dependable absolute accuracy.
This study presents a UAV photogrammetry and GIS-based workflow for generating high-accuracy three-dimensional cadastral models in urban environments. The proposed framework integrates RTK-enabled UAV image acquisition, ground control point (GCP) surveying, photogrammetric reconstruction, GIS-based spatial data management, and accuracy assessment within a unified workflow. A total of 454 aerial images were acquired and processed to generate a dense point cloud, digital surface model, orthomosaic, and textured 3D urban model. Positional accuracy was evaluated using 15 independently surveyed RTK GNSS checkpoints distributed throughout the study area. The results demonstrated a relative accuracy of 1.7 cm and an absolute positional accuracy of 2.47 cm based on independent checkpoint validation, confirming the suitability of the proposed workflow for large-scale cadastral mapping applications. The generated 3D cadastral model enabled accurate extraction and visualization of parcel boundaries, building footprints, and urban spatial features. The findings indicate that UAV photogrammetry combined with GIS provides a cost-effective and reliable approach for developing high-precision three-dimensional cadastral datasets that support modern land administration, urban planning, and digital city management.
Salar Mirzapour, Z. Azizi, H. Zavar et al.· Scientific Reports· 0 citations
Unmanned aerial vehicles are a modern technology for collecting data for aerial surveying to produce high-resolution digital elevation models (DEMs). This accuracy is achieved using ground control points (GCPs), which are specific locations on the ground with known coordinates that help improve the precision of aerial data collection. Digital elevation models are used in many applications such as topographic mapping, land-use planning, and levelling. This study aims to identify the optimum number of GCPs to achieve high accuracy for digital elevation models and reduced fieldwork. 1 km2 was imaged with a commercial UAV named Matrice 300 at a height of 200 m above the ground, with 80% forward overlap and 70% side overlap. 25 ground control points and 5 check points were created using the GPS technique. The images were processed using Agisoft Metashape software by an adjustment process with an incremental number of GCPs starting with 4 and ending with 25. The remaining points were used as a checkpoint to determine the precision of the model at each trial. Root Mean Square Error (RMSE) was used as an accuracy measurement. The study demonstrates that horizontal accuracy (RMSE XY) stabilizes after 5 ground control points (GCPs), with a marginal enhancement from 1.2 cm to 1.1 cm after 13 GCPs. The vertical accuracy (RMSE Z) improves markedly from 3.1 cm to 2.1 cm with 18 GCPs, demonstrating that height precision is more responsive to the quantity of control points. The 3D accuracy (RMSE XYZ) enhances by 1 cm with the addition of ground control points (GCPs) up to 18 but becomes stable at 2.3 cm after that, which is consistent with the vertical accuracy measurements. A medium GCP density of 9–12 is recommended for general UAV-based digital elevation model (DEM) generation, balancing accuracy and efficiency.
Kamal M. Gamal, A. Elshrkawy, Osama M. Moussa et al.· IOP Conference Series: Earth...· 0 citations
This study evaluates the metric reliability of nadir and hybrid RTK-UAV photogrammetric models for surface detail extraction on a two-story building without using Ground Control Points (GCPs). Two photogrammetric models were generated: a standard model based only on nadir images and a hybrid model combining nadir, oblique, and manual façade-oriented images. Both models were assessed using terrestrial reference data obtained from GNSS and reflector less total station measurements. The evaluation was performed at three levels: point-based, length-based, and surface-based comparisons. The point-based results indicate that the nadir model allowed 21 of the 35 reference points to be reconstructed, whereas the hybrid model allowed the 3D positions of all. The hybrid model also substantially improved vertical and overall 3D accuracy, reducing the ΔZ MAE from 0.355 m to 0.029 m and the 3D RMSE from 0.454 m to 0.046 m. In the length-based analysis, the nadir model was included where both endpoints of a selected linear element could be clearly identified. The nadir model allowed only 4 of the 14 selected length pairs to be measured, whereas the hybrid model allowed all 14 length pairs to be evaluated. On the other hand, the hybrid model had close agreement with the reference lengths, with a MAE of 0.012 m and RMSE of 0.016 m. Also, there is no statistically significant difference observed between reference and model lengths. In the surface-based comparison, the nadir model could represent only 4 of 7 reference surfaces, a limited number of reference surfaces, whereas the hybrid model enabled all selected surfaces to be evaluated, including upper-floor and under-eave regions. Although the nadir model produced lower average errors on some reconstructed surfaces, its limited surface coverage reduced its practical applicability. Overall, the findings demonstrate that hybrid RTK-UAV image acquisition provides a more robust and reliable solution than nadir-only acquisition for building surface documentation, particularly in façade areas with restricted visibility.
M. N. Alkan· International Journal of Geo...· 0 citations
The spatial distribution of ground control points (GCPs) is a critical factor affecting the accuracy of UAV photogrammetry in hilly terrain. In existing studies on GCP distribution, researchers have largely focused on planar uniformity metrics in flat terrain or on the effects of flight parameters in mountainous areas, with limited attention to the distinct roles of horizontal and vertical placement. In this study, we utilized a consumer-grade RTK-equipped UAV to acquire aerial imagery in a typical hilly area, with 27 high-precision GCPs deployed as a reference dataset. Four comparative experiments combining random/uniform distributions in both horizontal and vertical dimensions were designed to quantitatively analyze the impact of different distribution patterns on aerial triangulation and mapping accuracy. Our results demonstrate that the dual-uniform distribution strategy (i.e., uniform in both planimetric layout and elevation stratification) achieves the highest accuracy among the four tested configurations, with horizontal RMSE of 0.045 m and vertical RMSE of 0.039 m. Furthermore, we propose the Spatial Distribution Balance Index (SDBI), which integrates the Planar Uniformity Index (PUI) and Vertical Uniformity Index (VUI) with a terrain-adaptive weighting mechanism. The VUI weight, exemplified as β = 0.714 for this study area via a Sigmoid nonlinear amplification function (k = 15, x0 = 0.15), enables the SDBI to adaptively reflect terrain sensitivity to vertical control. The enhanced SDBI exhibits a correlation coefficient of r = −0.93 with final accuracy, validating its effectiveness as a GCP layout evaluation tool. In this study, we establish the SDBI as a diagnostic metric that quantitatively links GCP distribution characteristics to photogrammetric accuracy outcomes, providing both theoretical insights into anisotropic error propagation and practical guidance for deployment design in hilly regions.
Fei Jiang, Chengshuai Liu, Xiao-Feng Liu et al.· Applied Sciences· 0 citations
High-resolution spatial data is crucial for riverine modeling and flood mitigation. Traditional data often lacks necessary resolution or flexibility, making Unmanned Aerial Vehicles (UAVs) a transformative solution for generating precise Digital Elevation Models (DEMs). This systematic review analyzes 65 peer-reviewed studies published between 2014 and 2025. Following PRISMA guidelines, studies were selected based on specific inclusion and exclusion criteria focusing on riverine hydraulic applications to evaluate data acquisition methods, spatial accuracy, and operational challenges. The synthesis reveals a standard workflow using multirotor platforms, Structure from Motion (SfM) photogrammetry, and Ground Control Points (GCPs) to feed hydrodynamic models like HEC-RAS. While the literature consistently reports centimeter-level vertical accuracy—ideal for mapping flood inundation—critical challenges persist regarding the optical penetration of dense vegetation and submerged bathymetry. Ultimately, while UAV photogrammetry is a robust spatial analysis tool, advancing high-fidelity riverine analytics requires hybrid approaches integrating technologies like UAV-borne LiDAR and sonar. Creating these seamless topobathymetric models is essential for improving reliable flood risk management and informing effective environmental policy.
Nabil Muhamad, Yassir Arafat, A. Yunar· Journal of Geospatial Scienc...· 1 citation
Abstract. UAS photogrammetry has become an efficient solution for acquiring high-resolution geospatial data for urban mapping, environmental monitoring, and 3D modelling. However, mission planning still involves a trade-off between data quality and operational efficiency, particularly regarding flight altitude, which directly affects ground sample distance (GSD), point cloud density, and positional accuracy. This study evaluates the influence of flight altitude through a controlled comparison of two urban photogrammetric surveys: a low-altitude flight at 61.2 m (GSD = 1.56 cm/pix, 420 images) and a higher-altitude flight at 121 m (GSD = 3.11 cm/pix, 116 images). Both surveys used RGB cameras with equivalent image resolution mounted on different platforms, which constitutes an experimental limitation, while overlap and processing parameters were kept constant. The results show that the lower-altitude flight produced denser data and better geometric performance, with lower reprojection error and lower check point RMSE. In contrast, the higher-altitude flight provided greater operational efficiency, covering a larger area with fewer images and lower computational demand. These findings indicate that both strategies are technically viable but suited to different objectives: lower altitudes favour geometric detail and positional accuracy, whereas higher altitudes improve productivity and area coverage. Therefore, flight altitude should be selected according to project requirements, balancing geometric quality and operational efficiency.
Emanuel Amorim, Diogo Inojosa, Jailson Rodrigues et al.· The International Archives o...· 0 citations
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