Departamento de Ingeniería Cartográfica, Geodésica y Fotogrametría

URI permanente para esta comunidadhttps://hdl.handle.net/10953/36

En esta Comunidad se recogen los documentos generados por el Departamento de Ingeniería Cartográfica, Geodésica y Fotogrametría y que cumplen los requisitos de Copyright para su difusión en acceso abierto.

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Method for an automatic alignment of imagery and vector data applied to cadastral information in Poland
(Taylor&Francis, 2017-10-20) Ruiz Lendínez, Juan José; Maćkiewicz, Barbara; Motek, Pavel; Stryjakiewicz, Tadeusz
Nowadays, an important problem in combining vector data and imagery is that they rarely align. This problem can become particularly acute in the case of cadastral systems. In this study, and as part of the partnership between the Universities of Jaén and Adam Mickiewicz (Poznań), we provide a methodological proposal to assess the conflation procedures between cadastral vector data and imagery, improving the alignment between both data sets. To do this, we use an automatic alignment algorithm which detects road intersections from both data sets as control points by using image texture characterisation. With this method, we first train the system on the imagery to learn the road texture distribution, then we can obtain its segmentation according to its texture, and finally the system locates road intersection points. The last step is to align vector data and imagery by using different techniques. This algorithm is based on an earlier one, detailed in [Ruiz, J.J., Rubio, T.J., and Ureña, M.A., 2011b. Automatic extraction of road intersections from images in conflation processes based on texture characterization. Survey review, 43 (321), 212–225.]. However, in the updated version we have solved the problem of not-well-defined intersection points, resulting in a substantial increase in the number of intersection points employed for the final adjustment to align both products and in a reduction of the computation time. On the other hand, the positional uncertainty assessment of parcel boundary lines both before and after applying our alignment procedure between them is provided. With regard to the experimental results, in the case of Polish cadastral data this procedure allows for significant improvement in the alignment between imagery and cadastral parcels boundaries.
Influence of Sample Size on Automatic Positional Accuracy Assessment Methods for Urban Areas
(MDPI, 2018) Ariza-López, Francisco Javier; Ruiz-Lendínez, Juan José; Ureña, Manuel Antonio
In recent years, new approaches aimed to increase the automation level of positional accuracy assessment processes for spatial data have been developed. However, in such cases, an aspect as significant as sample size has not yet been addressed. In this paper, we study the influence of sample size when estimating the planimetric positional accuracy of urban databases by means of an automatic assessment using polygon-based methodology. Our study is based on a simulation process, which extracts pairs of homologous polygons from the assessed and reference data sources and applies two buffer-based methods. The parameter used for determining the different sizes (which range from 5 km up to 100 km) has been the length of the polygons’ perimeter, and for each sample size 1000 simulations were run. After completing the simulation process, the comparisons between the estimated distribution functions for each sample and population distribution function were carried out by means of the Kolmogorov–Smirnov test. Results show a significant reduction in the variability of estimations when sample size increased from 5 km to 100 km.
A method for checking the quality of geographic metadata based on ISO 19157
(Taylor & Francis, 2018) Ureña, Manuel Antonio; Nogueras-Iso, Javier; Lacasta, Javier; Ariza-López, Francisco Javier
With recent advances in remote sensing, location-based services and other related technologies, the production of geospatial information has exponentially increased in the last decades. Furthermore, to facilitate discovery and efficient access to such information, spatial data infrastructures were promoted and standardized, with a consideration that metadata are essential to describing data and services. Standardization bodies such as the International Organization for Standardization have defined well-known metadata models such as ISO 19115. However, current metadata assets exhibit heterogeneous quality levels because they are created by different producers with different perspectives. To address quality-related concerns, several initiatives attempted to define a common framework and test the suitability of metadata through automatic controls. Nevertheless, these controls are focused on interoperability by testing the format of metadata and a set of controlled elements. In this paper, we propose a methodology of testing the quality of metadata by considering aspects other than interoperability. The proposal adapts ISO 19157 to the metadata case and has been applied to a corpus of the Spanish Spatial Data Infrastructure. The results demonstrate that our quality check helps determine different types of errors for all metadata elements and can be almost completely automated to enhance the significance of metadata.
Displacements Study of an Earth Fill Dam Based on High Precision Geodetic Monitoring and Numerical Modeling
(MDPI, 2018-04-27) Acosta, Luis Enrique; de Lacy, Maria Clara; Ramos-Galán, Maria Isabel; Cano, Juan Pedro; Herrera-Olmo, Antonio Manuel; Avilés-Moreno, Manuel; Gil-Cruz, Antonio J.
The aim of this paper is to study the behavior of an earth fill dam, analyzing the deformations determined by high precision geodetic techniques and those obtained by the Finite Element Method (FEM). A large number of control points were established around the area of the dam, and the measurements of their displacements took place during several periods. In this study, high-precision leveling and GNSS (Global Navigation Satellite System) techniques were used to monitor vertical and horizontal displacements respectively. Seven surveys were carried out: February and July 2008, March and July 2013, August 2014, September 2015 and September 2016. Deformations were predicted, taking into account the general characteristics of an earth fill dam. A comparative evaluation of the results derived from predicted (FEM) and observed deformations shows the differences on average being 20 cm for vertical displacements, and 6 cm for horizontal displacements at the crest. These differences are probably due to the simplifications assumed during the FEM modeling process: critical sections are considered homogeneous along their longitude, and the properties of the materials were established according to the general characteristics of an earth fill dam. These characteristics were taken from the normative and similar studies in the country. This could also be due to the geodetic control points being anchored in the superficial layer of the slope when the construction of the dam was finished.
Assessing the accuracy of NRTK altimetric positioning for precision agriculture: test results in an olive grove environment in Southeast Spain
(Springer, 2018-07-24) Garrido-Carretero, María Selmira; de-Lacy, María Clara; Ramos-Galán, Maria Isabel; Borque, María Jesús; Susi, M
Soil erosion modeling in olive groves requires precise and accurate spatial data for the representation of topography associated with each time epoch considered. The precision and accuracy of altimetric values affect the quality of the digital elevation model (DEM) and therefore these requirements must be added to the necessity to generate high resolution DEMs. The increase of quality implies: 1. Improving the quality of the instrumentation and methodology applied in the field data collection and 2. Minimizing errors from the interpolation algorithm used to generate the digital terrain model. Currently, RTK networks are an indispensable complement to global navigation satellite systems (GNSS) precise positioning. The availability of highly accurate three-dimensional real time positioning has opened the door to new applications, making network-based real time kinematic (NRTK) positioning an attractive spatial data source for modeling soil erosion in small areas. This paper analyzes the quality of NRTK altimetric positioning supported by a local active network and its application in a test olive grove in SE Spain for soil erosion modeling. An evaluation procedure was implemented at several test sites distributed throughout an olive grove environment with special emphasis on filtering and checking the NRTK solutions in the vertical component. The precision in this component revealed a mean value of 15 mm and the vertical accuracy reached maximum values of 30 mm. In order to generate high resolution and accuracy DEM from the NRTK data, cross sections on the test olive grove were surveyed. The average altimetric quality value (CQ1D) of points surveyed was 0.017 m, according to the standard deviation estimated at test points. Based on the quality results, NRTK positioning is an accurate and reliable methodology for monitoring the erosion processes of small areas in an olive grove environment.
Low-cost GNSS receiver in RTK positioning under the standard ISO-17123-8: A feasible option in geomatics
(Elsevier, 2019) Garrido-Carretero, María Selmira; de-Lacy, María Clara; Borque, María Jesús; Ruiz-Armenteros, Antonio Miguel; Moreno-Guerrero, Rubén; Gil-Cruz, Antonio José
GNSS positioning is nowadays applied for surveying and other geomatic applications. Although dualfrequency GNSS receivers are widely used, low-cost single-frequency receivers have been relegated to navigation applications. However, their advantages make them optimum candidates for positioning applications in many scientific areas. To know the precision limits of these measuring systems, the evaluation of the uncertainty of measurement results obtained by them is required. For that, it is recommended to apply standard operating procedures (SOP). The International Organization for Standardization (ISO) published the standard ISO 17123-8 aimed at specifying field procedures to be adopted when determining and evaluating the precision of GNSS field measuring systems in real-time kinematic (RTK). Using this standard, we evaluate the positioning performance of two GNSS receivers, the geodetic dual-frequency Leica GS10 with AS10 antenna using a network RTK solution, and the low-cost single-frequency u-blox NEO-M8P using a single-base RTK solution. Considering the different sources of uncertainty and their influence quantities, the combined uncertainty budget for the dualfrequency receiver gives combined standard uncertainties on the horizontal position at the order of ±2.5 mm and close to ±4.5 mm for the vertical coordinate. In the case of the low-cost receiver, the combined standard uncertainties are close to ±5.5 mm for the horizontal position and ±11 mm for heights. The results indicate that just as the geodetic receiver satisfies the horizontal and vertical subcentimetric precision limits established for high precision applications, the low-cost receiver can achieve a competitive positioning performance to survey-grade receivers in real-time positioning for short baselines.
Dataset of three-dimensional traces of roads
(Nature Research, 2019) Ariza-López, Francisco Javier; Mozas, Antonio Tomás; Ureña, Manuel Antonio; Gil-de-la-Vega, Paula
We present a dataset consisting of three-dimensional traces, captured by Global Navigation Satellite System techniques with three-dimensional coordinates. It offers 138 traces (69 going and 69 returning), in addition to the actual mean axis of the road determined by precise surveying techniques to be used as ground truth for research activities. These data may serve as a test bed for research on data mining applications related to Global Navigation Satellite System multitraces, particularly the development and testing of algorithms intended for mining mean axis data from road multitraces. The data are suitable for the statistical analysis of both single-trace and multitrace datasets (e.g., outliers and biases).
Study of NSSDA Variability by Means of Automatic Positional Accuracy Assessment Methods
(MDPI, 2019) Ruiz-Lendínez, Juan José; Ariza-López, Francisco Javier; Ureña, Manuel Antonio
Point-based standard methodologies (PBSM) suggest using ‘at least 20’ check points in order to assess the positional accuracy of a certain spatial dataset. However, the reason for decreasing the number of checkpoints to 20 is not elaborated upon in the original documents provided by the mapping agencies which develop these methodologies. By means of theoretical analysis and experimental tests, several authors and studies have demonstrated that this limited number of points is clearly insufficient. Using the point-based methodology for the automatic positional accuracy assessment of spatial data developed in our previous study Ruiz-Lendínez, et al (2017) and specifically, a subset of check points obtained from the application of this methodology to two urban spatial datasets, the variability of National Standard for Spatial Data Accuracy (NSSDA) estimations has been analyzed according to sample size. The results show that the variability of NSSDA estimations decreases when the number of check points increases, and also that these estimations have a tendency to underestimate accuracy. Finally, the graphical representation of the results can be employed in order to give some guidance on the recommended sample size when PBSMs are used.
Analysing the positional accuracy of GNSS multi-tracks obtained from VGI sources to generate improved 3D mean axes
(Taylor & Francis, 2019) Mozas-Calvache, Antonio T.
The sharing of Global Navigation Satellite System (GNSS) tracks on the Internet is increasing enormously. Every day a great number of users capture routes using different devices and share these data. Individually these tracks present a poor positional accuracy because these devices obtain positions with accuracy of about 5-10 metres. In addition, they are usually captured for navigation and not for surveying. However, we can take advantage of the great quantity of tracks of the same linear element in order to obtain a more accurate solution. This study analyses this possibility using a wide set of tracks obtained in known conditions. We emulated those tracks obtained by Volunteered Geographic Information (VGI) users and we compared the mean axis obtained using all tracks with others obtained from a more accurate source. Additionally, we analyse the displacement of other axes obtained by varying several parameters such as the number of tracks and their length or by dividing the route into sections in function of sinuosity, etc. The results have shown an improved 3D mean axis and the viability of the method proposed in this study in order to use axes obtained from several tracks in maps at certain scales.
Measurement of Road Surface Deformation Using Images Captured from UAVs
(MDPI, 2019) Cardenal, J.; Fernández, T.; Pérez-García, J.L.; Gómez-Lopez, J.M.
This paper presents a methodology for measuring road surface deformation due to terrain instability processes. The methodology is based on ultra-high resolution images acquired from unmanned aerial vehicles (UAVs). Flights are georeferenced by means of Structure from Motion (SfM) techniques. Dense point clouds, obtained using the multiple-view stereo (MVS) approach, are used to generate digital surface models (DSM) and high resolution orthophotographs (0.02 m GSD). The methodology has been applied to an unstable area located in La Guardia (Jaen, Southern Spain), where an active landslide was identified. This landslide affected some roads and accesses to a highway at the landslide foot. The detailed road deformation was monitored between 2012 and 2015 by means of eleven UAV flights of ultrahigh resolution covering an area of about 260 m × 90 m. The accuracy of the analysis has been established in 0.02 ± 0.01 m in XY and 0.04 ± 0.02 m in Z. Large deformations in the order of two meters were registered in the total period analyzed that resulted in maximum average rates of 0.62 m/month in the unstable area. Some boundary conditions were considered because of the low required flying height (<50 m above ground level) in order to achieve a suitable image GSD, the fast landslide dynamic, continuous maintenance works on the affected roads and dramatic seasonal vegetation changes throughout the monitoring period. Finally, we have analyzed the relation of displacements to rainfalls in the area, finding a significant correlation between the two variables, as well as two different reactivation episodes.
Thematic Accuracy Quality Control by Means of a Set of Multinomials
(MDPI, 2019) Ariza-López, Francisco Javier; Rodríguez-Avi, José; Alba-Fernández, María Virtudes; García-Balboa, José Luis
The error matrix has been adopted as both the “de facto” and the “de jure” standard way to report on the thematic accuracy assessment of any remotely sensed data product. This perspective assumes that the error matrix can be considered as a set of values following a unique multinomial distribution. However, the assumption of the underlying statistical model falls down when true reference data are available for quality control. To overcome this problem, a new method for thematic accuracy quality control is proposed, which uses a multinomial approach for each category and is called QCCS (quality control column set). The main advantage is that it allows us to state a set of quality specifications for each class and to test if they are fulfilled. These requirements can be related to the percentage of correctness in the classification for a particular class but also to the percentage of possible misclassifications or confusions between classes. In order to test whether such specifications are achieved or not, an exact multinomial test is proposed for each category. Furthermore, if a global hypothesis test is desired, the Bonferroni correction is proposed. All these new approaches allow a more flexible way of understanding and testing thematic accuracy quality control compared with the classical methods based on the confusion matrix. For a better understanding, a practical example of an application is included for classification with four categories.
Prediction of the increase in health services demand based on the analysis of reasons of calls received by a customer relationship management
(Wiley, 2019-03-15) Ramos, Mª Isabel; Cubillas, Juan José; Jurado, Juan Manuel; Lopez, Wilfredo; Feito, Francisco R.; Quero, Manuel; Gonzalez, José María
Currently, customer relationship management (CRM) tools are very important in our society because they provide a comunication channel to the healthcare system for patients. Salud Responde is a CRM that provides many health services for the entire population of Andalusia, in southern Spain. The number and frequenzy of phone calls received change along the year. They depend on many factors, such as weekdays, seasons, vaccination campaigns, environmental factors, pandemic periods, etc. All these are the main reasons number of health calls changes along the year. This variability makes that the current management of resources for offering emergency services based on historical data is inefficient. The factors, which influence the phone calls along the year, are different from one period to another. Therefore, it is clear to demand an improved in the current management system. In this context, the main goal for this research is to develop an expert system able to identify and analyze, using different data mining algorithms, the most relevant factors to predict the variability of health service demand. Thus, here, it is proposed a methodology in which using reasons calls received in the CRM as input data, it is possible to predict in advance the healthcare resources demand.
How Much Nubia‐Eurasia Convergence Is Accommodated by the NE End of the Eastern Betic Shear Zone (SE Spain)? Constraints From GPS Velocities
(American Geophysical Union, 2019-04-29) Borque, María Jesús; Sánchez-Alzola, Alberto; Martín-Rojas, Iván; Alfaro, Pedro; Molina-Palacios, Sergio; Rosa-Cintas, Sergio; Rodríguez-Caderot, Gracia; de-Lacy, María Clara; García-Armenteros, Juan Antonio; Avilés-Moreno, Manuel; Herrera-Olmo, Antonio Manuel; García-Tortosa, Francisco Juan; Estévez-Rubio, Antonio; Gil-Cruz, Antonio José
We present the first GPS-derived geodetic observations from the NE end of the Eastern Betic Shear Zone obtained from the Bajo Segura GPS network (SE Spain). The network has 11 GPS sites and was sampled four times between 1999 and 2013. Despite the low signal-to-noise ratio of the residual velocities obtained, the velocities are nonzero at 95% confidence level. We postulate that the GPS data point to the partitioning of deformation into the NNW–SSE shortening and a N70E left-lateral component. The maximum deformation rates are located along the two main active faults in the study area. The maximum shortening rates (north component) in the southern region of the Bajo Segura Basin vary from west to east, ranging from 0.2 to 0.7 mm/year along the Bajo Segura Fault Zone. On the northern border of the basin, along the Crevillente Fault Zone, left-lateral displacement varies between 0.4 and 0.7 mm/year in the E-W direction. The GPS-based regional geodynamic models of the Western Mediterranean indicate that the residual shortening of the Eurasia-Nubia plate convergence is accommodated in the eastern part of the Iberian Peninsula and the Algero-Balearic Basin. Our results indicate that part of this residual deformation occurs at the NE end of the Eastern Betic Shear Zone, but significant deformation must be accommodated also to the north (External Betics) and to the south (Cartagena Basin and offshore area). We postulate that Eurasia-Nubia plate convergence is transferred to the Eastern Betics because of the thin and rigid (potentially oceanic) crust of the Algero-Balearic Basin, which acts as an indenter.
Study of NSSDA Variability by Means of Automatic Positional Accuracy Assessment Methods
(MDPI, 2019-12-02) Ruiz-Lendínez, Juan José; Ariza-López, Francisco Javier; Ureña, Manuel Antonio
Point-based standard methodologies (PBSM) suggest using ‘at least 20’ check points in order to assess the positional accuracy of a certain spatial dataset. However, the reason for decreasing the number of checkpoints to 20 is not elaborated upon in the original documents provided by the mapping agencies which develop these methodologies. By means of theoretical analysis and experimental tests, several authors and studies have demonstrated that this limited number of points is clearly insu cient. Using the point-based methodology for the automatic positional accuracy assessment of spatial data developed in our previous study Ruiz-Lendínez, et al (2017) and specifically, a subset of check points obtained from the application of this methodology to two urban spatial datasets, the variability of National Standard for Spatial Data Accuracy (NSSDA) estimations has been analyzed according to sample size. The results show that the variability of NSSDA estimations decreases when the number of check points increases, and also that these estimations have a tendency to underestimate accuracy. Finally, the graphical representation of the results can be employed in order to give some guidance on the recommended sample size when PBSMs are used.
Multitemporal analysis of gully erosion in olive groves by means of digital elevation models obtained with aerial photogrammetric and LiDAR data
(MDPI, 2020) Fernández, T.; Perez-García, J.L.; Gómez-López, J.M; Cardenal, J; Calero, J.; Sánchez-Gómez, M.; Delgado, J.; Tovar-Pescador, J.
La erosión en cárcavas es uno de los principales procesos de degradación del suelo y representa entre el 50% y el 90% de la erosión total a escala de cuenca. Por tanto, su caracterización precisa ha recibido una atención creciente en los últimos años. Las técnicas geomáticas, principalmente fotogrametría y LiDAR, pueden apoyar el análisis cuantitativo en la formación y el desarrollo de cárcavas. Este artículo aborda la aplicación de estas técnicas utilizando fotografías aéreas y datos LiDAR aéreos, disponibles en servidores de bases de datos públicos, para identificar y cuantificar la erosión de cárcavas a lo largo de un período bastante prolongado (1980-2016) en un área de 7,5 km2 de olivar. Se orientaron varios vuelos históricos (1980, 1996, 2001, 2005, 2009, 2011, 2013 y 2016) en un sistema de referencia de coordenadas común con la nube de puntos LiDAR, cuya calidad fue previamente testeada con puntos medidos con GNSS sobre el terreno. A partir de los vuelos orientados, se obtuvieron modelos digitales de superficie (MDS) y ortofotografías. A continuación, el análisis del MDS de diferencias permitió la identificación de cárcavas, el cálculo de las áreas afectadas, así como la estimación de diferencias de altura y volúmenes entre modelos, considerando una incertidumbre estimada de ± 1 m. Estos análisis dan como resultado una incisión promedio de 0,50 m y una pérdida de volumen de 85000 m3 en el área de la cárcava, con algunos períodos (2009-2011 y 2011-2013) mostrando tasas de 10000 a 20000 m3/año (20 a 40 t/ha* año). Estos periodos correspondieron a años donde se produjeron episodios lluviosos destacados en la región, lo que condujo a una mayor actividad erosiva. En el periodo 2009-2011 destacó fundamentalmente un proceso de incisión, mientras que a partir de 2011-2013 el mecanismo fue de ensanchamiento de la cárcava. La edición manual de MDS para la obtención de modelos digitales de elevación (MDT) de un sector de detalle ha permitido analizar la influencia de esta operación en los cálculos de erosión, encontrando que no es significativa salvo en zonas de cárcavas con forma muy pronunciada.
Accuracy Assessment of Digital Elevation Models (DEMs): A Critical Review of Practices of the Past Three Decades
(MDPI, 2020) Mesa-Mingorance, José Luis; Ariza-López, Francisco Javier
An analysis of almost 200 references has been carried out in order to obtain knowledge about the DEM (Digital Elevation Model) accuracy assessment methods applied in the last three decades. With regard to grid DEMs, 14 aspects related to the accuracy assessment processes have been analysed (DEM data source, data model, reference source for the evaluation, extension of the evaluation, applied models, etc.). In the references analysed, except in rare cases where an accuracy assessment standard has been followed, accuracy criteria and methods are usually established according to the premises established by the authors. Visual analyses and 3D analyses are few in number. The great majority of cases assess accuracy by means of point-type control elements, with the use of linear and surface elements very rare. Most cases still consider the normal model for errors (discrepancies), but analysis based on the data itself is making headway. Sample size and clear criteria for segmentation are still open issues. Almost 21% of cases analyse the accuracy in some derived parameter(s) or output, but no standardization exists for this purpose. Thus, there has been an improvement in accuracy assessment methods, but there are still many aspects that require the attention of researchers and professional associations or standardization bodies such as a common vocabulary, standardized assessment methods, methods for meta-quality assessment, and indices with an applied quality perspective, among others.
Effects on the Double Bounce Detection in Urban Areas Based on SAR Polarimetric Characteristics
(MDPI, 2020) Delgado Blasco, José Manuel; Fitrzyk, Magdalena; Patruno, Jolanda; Ruiz-Armenteros, Antonio M.; Marconcini, Mattia
Abandoned Farmland Location in Areas A ected by Rapid Urbanization Using Textural Characterization of High Resolution Aerial Imagery
(MDPI, 2020-03-25) Ruiz Lendínez, Juan José
Several studies have demonstrated that farmland abandonment occurs not only in rural areas, but is also closely interlinked with urbanization processes. Therefore, the location of abandoned land and the registration of the spatial information referring to it play important roles in urban land management. However, mapping abandoned land or land in the process of abandonment is not an easy task because the limits between the di erent land uses are not clear and precise. It is therefore necessary to develop methods that allow estimating and mapping this type of land as accurately as possible. As an alternative to other geomatics methods such as satellite remote sensing, our approach proposes a framework for automatically locating abandoned farmland in urban landscapes using the textural characterization and segmentation of aerial imagery. Using the city of Pozna´n (Poland) as a case study, results demonstrated the feasibility of applying our approach, reducing processing time and workforce resources. Specifically and by comparing the results obtained with the data provided by CORINE Land Cover, 2275 ha (40.3%) of arable land within the city limits were abandoned, and the area of abandoned arable land was almost 9.2% of the city’s area. Finally, the reliability of the proposed methodology was assessed from two di erent focuses: (i) the accuracy of the segmentation results (from a positional point of view) and (ii) the e ciency of locating abandoned land (as a specific type of land use) in urban areas particularly a ected by rapid urbanization.
The Impact of Canopy Reflectance on the 3D Structure of Individual Trees in a Mediterranean Forest
(MDPI, 2020-05-01) Jurado, J; Ramos, M.I; Enríquez, C; Feito, F
The characterization of 3D vegetation structures is an important topic, which has been addressed by recent research in remote sensing. The forest inventory requires the proper extraction of accurate structural and functional features of individual trees. This paper presents a novel methodology to study the impact of the canopy reflectance on the 3D tree structure. A heterogeneous natural environment in a Mediterranean forest, in which various tree species (pine, oak and eucalyptus) coexist, was covered using a high-resolution digital camera and a multispectral sensor. These devices were mounted on an Unmanned Aerial Vehicle (UAV) in order to observe the tree architecture and the spectral reflectance at the same time. The Structure from Motion (SfM) method was applied to model the 3D structures using RGB images from the high-resolution camera. The geometric accuracy of the resulting point cloud was validated by georeferencing the study area through multiple ground control points (GCPs). Then, the point cloud was enriched with the reflected light in four narrow-bands (green, near-infrared, red and red-edge). Furthermore, the Normalized Difference Vegetation Index (NDVI) was calculated in order to measure the tree vigor. A comprehensive analysis based on structural and spectral features of individual trees was proposed. A spatial segmentation was developed to detect single-trees in a forest and for each one to identify the crown and trunk. Consequently, structural parameters were extracted, such as the tree height, the diameter at breast height (DBH) and the crown volume. The validation of these measurements was performed by field data, which were taken using a Total Station (TS). In addition, these characteristics were correlated with the mean reflectance in the tree canopy. Regarding the observed tree species, a statistical analysis was carried out to study the impact of reflectance on the 3D tree structure. By applying our method, a more detailed knowledge of forest dynamics can be gained and the impact of available solar irradiance on single-trees can be analyzed.
The UAS-Based 3D Image Characterization of Mozarabic Church Ruins in Bobastro (Malaga), Spain
(MDPI, 2020-07-24) Enríquez, Carlos; Jurado-Rodríguez, Juan Manuel; Bailey, Alexandro; Callén, Danilo; Collado, María José; Espina, Gabriel; Marroquín, Pablo; Oliva, Erick; Osla, Edgar; Ramos-Galán, Maria Isabel; Sarceño, Scarlett; Feito, Francisco Ramón
In recent years, the application of geomatics tools in archaeology has proved to be very useful to obtain meaningful knowledge of the 3D reconstruction of archaeological remains and semantic classification of the 3D surface. These techniques have proven to be an effective solution for the 3D modeling and the extraction of many spatial features on an archaeological site. However, novel methodologies as well as new data exploitation strategies are required to exploit these geospatial data for natural and cultural heritage documentation, monitoring, and preservation. In this paper, we have studied unique archaeological ruins, a Mozarab church in Al-Andalus, using high-resolution RGB images, which was taken by a drone. Thus, a 3D reconstruction of the ruins and the surrounding environment is carried out in order to characterize it on a dense point cloud. Then, a digital elevation model (DEM) was calculated in order to identify critical slope lines, which are significant to determine where the structure of the church was built. Our results can be used for the development of an architectural project and thus a virtual recreation of these archaeological ruins was performed

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