Influence of AGL flight and off-nadir images on UAV-SfM accuracy in complex morphology terrains

In the field of geosciences and engineering, situations arise where special attention have to be paid to the planning of the UAVphotogrammetric project, that is, terrain with complex geometry and steep slopes. The use of off-nadir imagery and flights at a fixed height above ground level (AGL) are postulated as possible factors to be considered to achieve high accuracies. The objective of this study is to evaluate the influence of image angle, frontal and side overlaps, and type of flight (above mean sea level (AMSL) or AGL), on the accuracy of the dense 3D point cloudyielded by UAV-SfM. The results obtained showed that imagery with an angle between 20 and 35 in two perpendicular flight line directions, 90/90, 90/70 or 70/70 overlap and AGL flight is the optimal combination for best accuracy and high precision. With nadir imagery, the combination of factors that gives the most accuracy results are AGL flights with a 90/70 overlap

A Comparative Analysis of Phytovolume Estimation Methods Based on UAV-Photogrammetry and Multispectral Imagery in a Mediterranean Forest

Management and control operations are crucial for preventing forest fires, especially in Mediterranean forest areas with dry climatic periods. One of them is prescribed fires, in which the biomass fuel present in the controlled plot area must be accurately estimated. The most used methods for estimating biomass are time-consuming and demand too much manpower. Unmanned aerial vehicles (UAVs) carrying multispectral sensors can be used to carry out accurate indirect measurements of terrain and vegetation morphology and their radiometric characteristics. Based on the UAV-photogrammetric project products, four estimators of phytovolume were compared in a Mediterranean forest area, all obtained using the difference between a digital surface model (DSM) and a digital terrain model (DTM). The DSM was derived from a UAV-photogrammetric project based on the structure from a motion algorithm. Four different methods for obtaining a DTM were used based on an unclassified dense point cloud produced through a UAV-photogrammetric project (FFU), an unsupervised classified dense point cloud (FFC), a multispectral vegetation index (FMI), and a cloth simulation filter (FCS). Qualitative and quantitative comparisons determined the ability of the phytovolume estimators for vegetation detection and occupied volume. The results show that there are no significant differences in surface vegetation detection between all the pairwise possible comparisons of the four estimators at a 95% confidence level, but FMI presented the best kappa value (0.678) in an error matrix analysis with reference data obtained from photointerpretation and supervised classification. Concerning the accuracy of phytovolume estimation, only FFU and FFC presented differences higher than two standard deviations in a pairwise comparison, and FMI presented the best RMSE (12.3 m) when the estimators were compared to 768 observed data points grouped in four 500 m2 sample plots. The FMI was the best phytovolume estimator of the four compared for low vegetation height in a Mediterranean forest. The use of FMI based on UAV data provides accurate phytovolume estimations that can be applied on several environment management activities, including wildfire prevention. Multitemporal phytovolume estimations based on FMI could help to model the forest resources evolution in a very realistic way

Use of UAV-Photogrammetry for Quasi-Vertical Wall Surveying

In this study, an analysis of the capabilities of unmanned aerial vehicle (UAV) photogrammetry to obtain point clouds from areas with a near-vertical inclination was carried out. For this purpose, 18 different combinations were proposed, varying the number of ground control points (GCPs), the adequacy (or not) of the distribution of GCPs, and the orientation of the photographs (nadir and oblique). The results have shown that under certain conditions, the accuracy achieved was similar to those obtained by a terrestrial laser scanner (TLS). For this reason, it is necessary to increase the number of GCPs as much as possible in order to cover a whole study area. In the event that this is not possible, the inclusion of oblique photography ostensibly improves results; therefore, it is always advisable since they also improve the geometric descriptions of break lines or sudden changes in slope. In this sense, UAVs seem to be a more economic substitute compared to TLS for vertical wall surveying

Development and assessment of a prototype as an innovative method for teaching agricultural machinery

An educational variable‐rate application (VRA) sprayer was developed and laboratory tested at the University of Seville (Spain). It was designed and built during 2009 by the undergraduate engineering students in a Precision Agriculture course and used as a teaching model in an Agricultural Machinery course during 2010. The first stage involved mounting all the instrumentation, sensors, and the hydraulic system on a metal platform. The second stage involved mounting a DGPS receiver, flowmeter, automated application control system, and all necessary electrical connections to the platform. Preliminary calibration tests of the equipment at a constant speed of 0.375 m s‐1 (1.35 km h‐1) showed good performance for pressure (kPa) and application rate (L ha‐1) (R2 = 0.998, p < 0.001). To evaluate the teaching method based on the prototype, a short‐answer assessment test was conducted consisting of ten multiple‐choice questions, each with one possible correct answer. Data were analyzed using analysis of variance (ANOVA). The factors were the teaching method (TM), repeated course (R), and attended theory (AT). In addition, the effect of a covariate (number of times a student repeated the course) in the factors was controlled with an analysis of covariance (ANCOVA). The effect of teaching method was significant for the score on the VRA sprayer questions (SPS) variable and the score on the conventional sprayer questions (SCS) variable (p < 0.001 for both). The average success for students using the prototype sprayer was 86%, compared to 60% for those using a conventional sprayer. The total cost of the VRA prototype sprayer was 40% less than the cost of retrofitting a conventional sprayer with precision agriculture equipment. Since the students were engaged in their own learning, they maintained a high level of enthusiasm throughout the course when utilizing the VRA prototype sprayer. It has proved to be a complementary and beneficial alternative for improving the students' education in the Agricultural Machinery course

Editorial for Special Issue “UAV Photogrammetry and Remote Sensing”

The concept of Remote Sensing as a way of capturing information from an object without making contact with it has, until recently, been exclusively focused on the use of earth observation satellites [...

Homework encouragement by means of peer reviewed activities and global group tutorials

Se parte de la detección de una serie de carencias en la adquisición de conocimientos en la asignatura Motores y Máquinas de 2.º curso del Grado en Ingeniería Agroalimentaria y del Medio Rural. Para dirigir y motivar al alumnado de cara a la superación de la asignatura se organizaron dos prácticas fuera del aula (P2 y P3), de la misma naturaleza que los tres tipos de ejercicios de examen (P1, P2 y P3). La corrección de las prácticas se hizo mediante evaluación por pares y posterior revisión del profesorado. La realización de las dos prácticas tuvo un seguimiento desigual, con una tasa de evaluación de 33 y 22 % respectivamente, mientras que la tasa de éxito fue muy elevada, 87 y 97 %. En cuanto a los resultados del examen, la tasa de evaluación fue del 59 y 55 %, y la tasa de éxito del 50 y 36 %, inferior a la registrada en las prácticas. Sin embargo la tasa de rendimiento fue similar entre el examen (30 - 20 %) y las prácticas (29 y 12 %). Los resultados de los exámenes del curso 2016/17 fueron mejores que en los exámenes del curso 2015/16, por lo tanto se ha cumplido el objetivo de mejorar el porcentaje de alumnos que superan la asignatura, mejorando o manteniendo el rendimiento. Por último, la tasa de evaluación no mostró un resultado satisfactorio en las prácticas, por lo que se hace necesario incidir entre el alumnado en la importancia de estas actividades.Firstly, it has been detected some deficiencies in the acquisition of knowledge for the subject “Motores y Máquinas” corresponding to the 2nd year of the Degree in Agri-food Engineering and Rural Environment. Two homework practices (P2 and P3), similar to the three types of exam exercises (P1, P2 and P3) were organized to tutorize and motivate students in order to pass the subject. Practices correction was done through peer evaluation and subsequent revision of the teaching staff. The performance of the two practices was unevenly followed, with an evaluation rate of 33 and 22% respectively, while the success rate was very high, 87 and 97%. Regarding the results of the examination, the evaluation rate was 59 and 55% and the success rate was of 50 and 36% for P2 and P3 respectively, lower than that recorded in the practices. However, the rate of performance was similar between exam (30 - 20%) and practices (29 and 12%). The results of the 2016/17 exams were better than in the examinations of the 2015/16 course, therefore the objective of improving the percentage of students who pass the subject, improving or maintaining the performance has been accomplish. Finally, the evaluation rate did not show a satisfactory result for the practices, for this reason, it is necessary to persuade the students to the importance of these activities

Development of a Telemetry and Yield-Mapping System of Olive Harvester

Sensors, communication systems and geo-reference units are required to achieve an optimized management of agricultural inputs with respect to the economic and environmental aspects of olive groves. In this study, three commercial olive harvesters were tracked during two harvesting seasons in Spain and Chile using remote and autonomous equipment that was developed to determine their time efficiency and effective based on canopy shaking for fruit detachment. These harvesters work in intensive/high-density (HD) and super-high-density (SHD) olive orchards. A GNSS (Global Navigation Satellite System) and GSM (Global System for Mobile Communications) device was installed to track these harvesters. The GNSS receiver did not affect the driver’s work schedule. Time elements methodology was adapted to the remote data acquisition system. The effective field capacity and field efficiency were investigated. In addition, the field shape, row length, angle between headland alley and row, and row alley width were measured to determinate the optimum orchard design parameters value. The SHD olive harvester showed significant lower effective field capacity values when alley width was less than 4 m. In addition, a yield monitor was developed and installed on a traditional olive harvester to obtain a yield map from the harvested area. The hedge straddle harvester stood out for its highly effective field capacity; nevertheless, a higher field efficiency was provided by a non-integral lateral canopy shaker. All of the measured orchard parameters have influenced machinery yields, whether effective field capacity or field efficiency. A saving of 40% in effective field capacity was achieved with a reduction from 4 m or higher to 3.5 m in alley width for SHD olive harvester. A yield map was plotted using data that were acquired by a yield monitor, reflecting the yield gradient in spite of the larger differences between tree yield

Variables que influyen en la fijación de precios en el transporte aéreo : el caso de la ruta Madrid-Barcelona

El objetivo del presente trabajo es analizar el efecto de una serie de variables sobre la fijación de precios en el transporte aéreo. A tal fin se analizan las variaciones de precios en función de variables como las estrategias de las diversas compañías que cubren la ruta, la cercanía a la fecha de salida, el día de la semana o el horario de salida del vuelo. Para el análisis se han utilizado datos de la ruta Madrid-Barcelona, la más frecuentada de las rutas aéreas europeas en la fecha de obtención de datos.This paper purpose is to examine the effect that some variables have on the prices setting in air transport. The prices variation is analysed related to variables as air transport companies strategies, the time to the flight departure, the day of the week or the flight schedule. The Madrid-Barcelona air route has been chosen because it is the more frequented air route in Europe

UAV Photogrammetry Accuracy Assessment for Corridor Mapping Based on the Number and Distribution of Ground Control Points

Unmanned aerial vehicle (UAV) photogrammetry has recently emerged as a popular solution to obtain certain products necessary in linear projects, such as orthoimages or digital surface models. This is mainly due to its ability to provide these topographic products in a fast and economical way. In order to guarantee a certain degree of accuracy, it is important to know how many ground control points (GCPs) are necessary and how to distribute them across the study site. The purpose of this work consists of determining the number of GCPs and how to distribute them in a way that yields higher accuracy for a corridor-shaped study area. To do so, several photogrammetric projects have been carried out in which the number of GCPs used in the bundle adjustment and their distribution vary. The different projects were assessed taking into account two different parameters: the root mean square error (RMSE) and the Multiscale Model to Model Cloud Comparison (M3C2). From the different configurations tested, the projects using 9 and 11 GCPs (4.3 and 5.2 GCPs km−1, respectively) distributed alternatively on both sides of the road in an offset or zigzagging pattern, with a pair of GCPs at each end of the road, yielded optimal results regarding fieldwork cost, compared to projects using similar or more GCPs placed according to other distributions