Assessing the geometric accuracy of UAV-based orthophotos

2020

This paper attempts to research and investigate geometric quality of an Unmanned Aerial Orthophoto from DJI Phantom 4 Pro for map generation and compilation despite the fact that a fewer number of control points were used and this was then compared with same points as observed from a Hi Target V30 GNSS Receiver in Real Time Kinematic (RTK) mode. Two important criteria are pivotal to Geometric quality assessment of an Aerial photograph; Geometric accuracy and Object-definition property while this research focused on the geometric accuracy as compared to another method of terrestrial data acquisition using GNSS. In remote sensing and photogrammetric operations, the geometric quality of the imagery purely depends on the relation between pixel size and the map scale including contrast information, atmospheric condition, the sun elevation, the printing technology and the screen resolution. The Unmanned Aircraft System (UAS) deliverables which include the Orthophoto and the Digital Surfac...

The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2019

In the domain of land administration, UAV-based orthophotos are gaining in importance as base data to support the extraction of cadastral boundaries and further visual interpretation, manual digitization, or automated feature detection procedures. However, the fact that UAV-derived geographical information can support decision-making processes that involve people's land rights ultimately raises questions about the quality of the respective data. Especially geometric accuracy and radiometry can be negatively influenced by poor flight planning, densely populated areas, and adverse meteorological conditions. Thus, this paper takes a closer look at optimal workflows to minimize the need for ground truthing by presenting an experimental assessment of flight parameters and ground truth methods. More than 40 datasets entail the representative basis to investigate the impact on the absolute geometric accuracy of derived UAV-based orthomosaics. Results suggest that UAV data acquisition workflows can cover a wide range of data quality depending on UAV equipment, flight planning parameters and ground truthing strategies. Ultimately, this paper can help to determine the best approach to provide a high-quality data product that satisfies end user and supports the provision of reliable base data for automated or manual extraction of cadastral boundaries.

IOP Conference Series: Earth and Environmental Science, 2014

Unmanned Aerial Vehicle or UAV is extensively applied in various fields such as military applications, archaeology, agriculture and scientific research. This study focuses on topographic mapping and map updating. UAV is one of the alternative ways to ease the process of acquiring data with lower operating costs, low manufacturing and operational costs, plus it is easy to operate. Furthermore, UAV images will be integrated with QuickBird images that are used as base maps. The objective of this study is to make accuracy assessment and comparison between topographic mapping using UAV images integrated with aerial photograph and satellite image. The main purpose of using UAV image is as a replacement for cloud covered area which normally exists in aerial photograph and satellite image, and for updating topographic map. Meanwhile, spatial resolution, pixel size, scale, geometric accuracy and correction, image quality and information contents are important requirements needed for the generation of topographic map using these kinds of data. In this study, ground control points (GCPs) and check points (CPs) were established using real time kinematic Global Positioning System (RTK-GPS) technique. There are two types of analysis that are carried out in this study which are quantitative and qualitative assessments. Quantitative assessment is carried out by calculating root mean square error (RMSE). The outputs of this study include topographic map and orthophoto. From this study, the accuracy of UAV image is ± 0.460m. As conclusion, UAV image has the potential to be used for updating of topographic maps.

IEEE, 2019

Now a day's Unmanned Aerial Vehicle (UAV) replaces the aeroplane flown by a pilot, and a small high-resolution digital camera replaces the large metric camera, the combination of both are used as a platform for acquiring aerial images, so as called UAV photogrammetry. This study concentrates on the use and the capabilities of UAV photogrammetry for producing topographic maps, and to assess the accuracy of these maps. For that, a lightweight fixed-wing UAV eBee-Sensefly was used as a platform for acquiring aerial digital images of the study area. Before the flight mission, ground control points were established, Leica GS15 GPS determined their 3D coordinates in two sessions of static observations. The digital images were processed using Pix4Dmapper software for producing orthophotos and digital surface models. For accuracy assessment, the root mean square errors (RMSE) is used in which 2.0 cm in Easting, 2.1 cm in Northing and 7.5 cm in Elevation were obtained for orthomosaic and DTM respectively. Based on these assessments, the results showed that the accuracy achieved is following (ASPRS Accuracy Standards for Digital Geospatial Data) within the second and third classes of these standards for horizontal and vertical accuracies. In conclusion, this study shows that UAV photogrammetry can be applied for producing digital maps, orthophotos, contour lines, digital terrain model, digital surface model, and line maps all of them complies with international standards.

Journal on Geoinformatics, Nepal

This study aims to produce accurate geospatial 3D data from unmanned aerial vehicle (UAV) images. An image of approx. 1 km2 area of the Banepa-10, Kabhrepalanchok district was captured using a DJI Mavic Pro drone. Pix4dmapper programs were used to generate the solution. The horizontal and vertical accuracies of the obtained UAV solution were computed by comparing the coordinates of 5 Ground Control Points (GCPs) with coordinates measured using the static DGPS observation method. The root mean square error (RMSE) was calculated during geo-referencing of Orthomosaic and obtained a value of 0.006.Mainly, three comparisons were made for parcels digitized from the Orthomosaic image w.r.t to Total Station and Tape measurement ; Area, Perimeter and Centroid Position. Cadastral survey using Total station, UAV and Tape measurement were confirmed to be comparable in terms of accuracy, completeness, and expenditure of time. From the result of this study, the area as well perimeter of parcels o...

European Journal of Remote Sensing

Geometric accuracy is an important attribute of cartographic products and UAV photogrammetry has been gaining market in topographic mapping thanks to high spatial and temporal resolution, however, they need proper evaluation following accuracy standards and protocols. Regarding this, this work evaluates products from digital photogrammetry from images acquired with a fixed-wing UAV (18Mpixel camera) in a 300-380m height flight over a Hydroelectric Power Plant (HPP) in Brazil. A dataset of 23 ground control points assessed with an RTK-GNSS (using natural targets) was validated with its homologous in the Digital Surface Model (DSM) and the orthomosaic, following a workflow in which the appropriate statistics were applied. Following parametric tests like the Students t-test and the Chi-square, we compared the results with the Brazilian Cartographic Standard for digital cartography, achieving minimum scale of 1: 20,000 (RMSE of 1.04 m) for the orthomosaic, and minimum scale of 1: 10,000 (RMSE of 1.31 m) for the elevation in the DSM, although, no special targets were used. As the 3D mapping generated using the photogrammetry still needs a protocol to evaluate the accuracy, this work applied a proposed workflow respecting the quality of the data to meet the requirements of the cartographic standard.

KnE Engineering, 2019

Orthophoto mosaic is assembled from aerial perspective images through a process called orthorectification, which eliminate photographic tilts and terrain relief effects. These orthorectified images have been resampled from the original ones that may have been prepared from a DTM which does not accurately model the surface. Meanwhile, some proprietary software such as Agisoft utilizes spatially dense 3D point clouds that are generated from a so called Structure from Motion technique to generate the orthophoto. The software provides a black-box method to regard these clouds as DSM, and it utilizes this surface model to project pixels from the original images. This paper investigates geometric accuracy of the produced orthophoto mosaic according to the American Society of Photogrammetry and Remote Sensing (ASPRS) standards. To minimize scale differences among images, a 35mm fixed-lens camera is mounted on a fixed-wing UAV platform. Flight missions are carried out at around 250m flying ...

IOP Conference Series: Earth and Environmental Science, 2014

Photogrammetry is the earliest technique used to collect data for topographic mapping. The recent development in aerial photogrammetry is the used of large format digital aerial camera for producing topographic map. The aerial photograph can be in the form of metric or non-metric imagery. The cost of mapping using aerial photogrammetry is very expensive. In certain application, there is a need to map small area with limited budget. Due to the development of technology, small format aerial photogrammetry technology has been introduced and offers many advantages. Currently, digital map can be extracted from digital aerial imagery of small format camera mounted on light weight platform such as unmanned aerial vehicle (UAV). This study utilizes UAV system for large scale stream mapping. The first objective of this study is to investigate the use of light weight rotary-wing UAV for stream mapping based on different flying height. Aerial photograph were acquired at 60% forward lap and 30% sidelap specifications. Ground control points and check points were established using Total Station technique. The digital camera attached to the UAV was calibrated and the recovered camera calibration parameters were then used in the digital images processing. The second objective is to determine the accuracy of the photogrammetric output. In this study, the photogrammetric output such as stereomodel in three dimensional (3D), contour lines, digital elevation model (DEM) and orthophoto were produced from a small stream of 200m long and 10m width. The research output is evaluated for planimetry and vertical accuracy using root mean square error (RMSE). Based on the finding, sub-meter accuracy is achieved and the RMSE value decreases as the flying height increases. The difference is relatively small. Finally, this study shows that UAV is very useful platform for obtaining aerial photograph and subsequently used for photogrammetric mapping and other applications.

Attempt has been made in this research to investigate suitability of an Unmanned Aerial Photograph from Trimble UX5 Aerial imaging solution for Map generation and Compilation. Two important criteria are pivotal to Geometric quality assessment of an Aerial photograph; Geometric accuracy and Objectdefinition property. In Remote Sensing and Photogrammetric operations, the Geometric quality of the imagery basically depends on the relation between pixel size and the map scale, contrast information, atmosphere and the sun elevation, the printing technology, screen resolution and the visual acuity. The Unmanned Aircraft System (UAS) deliverables which are the Orthophoto and the Digital Surface Model show that UAS (Trimble UX5) can be used for compilation of large scale maps based on the map accuracy analysis of the National Standard for Spatial Data Accuracy (NSSDA, 1998). The horizontal accuracy of 3.207m (RMSE: 1.85m) and vertical accuracy of 0.884m (RMSE: 0.45m) were obtained which falls within the allowable misclosure, the object definition properties of the products were also observed and found to be suitable for Cadastral Map compilation.

Reports on Geodesy and Geoinformatics

The main purpose of this work is to confirm the possibility of making largescale orthophotomaps applying unmanned aerial vehicle (UAV) Trimble- UX5. A planned altitude reference of the studying territory was carried out before to the aerial surveying. The studying territory has been marked with distinctive checkpoints in the form of triangles (0.5 × 0.5 × 0.2 m). The checkpoints used to precise the accuracy of orthophotomap have been marked with similar triangles. To determine marked reference point coordinates and check-points method of GNSS in real-time kinematics (RTK) measuring has been applied. Projecting of aerial surveying has been done with the help of installed Trimble Access Aerial Imaging, having been used to run out the UX5. Aerial survey out of the Trimble UX5 UAV has been done with the help of the digital camera SONY NEX-5R from 200m and 300 m altitude. These aerial surveying data have been calculated applying special photogrammetric software Pix 4D. The orthophotomap ...