Optimal Parameters for DEM Extraction from IKONOS Data: A Case Study of a Coastal Area

The gap between aerial and satellite photogrammetry is getting smaller as both systems have benefited from great technology improvements in the last years. However, the major advantage of earth observation satellites continues to be the possibility to acquire data virtually anywhere on the planet without considering border and logistical restrictions and over huge extensions. A pair of stereo images corresponding to a coastal area in the NW of Spain is the basis for this paper, which analyzes certain influential variables in the process of generating a Digital Elevation Model (DEM) from stereoscopic pairs of IKONOS images. The mathematical model, the number of Ground Control Points (GCPs) and their accuracies are analyzed through a sequence of experimental trials. Two main methods are applied for math modeling: a CCRS model (rigorous model) and a Rational Functions model. The influence of the GCPs’ positional quality is compared using two different information sources: points measured in 1:5,000 cartography and points surveyed via GPS. The number of GCPs tested varies between 0 and 20. Using different configurations of these variables, 17 models are generated. The best results are achieved with the rigorous model and 16 GCPs measured with GPS with an RMSE of 1.01 m (or an LE95 –Linear Error in Z at 95% confidence level- of 2 m), which is approximately the pixel size of the initial pair. The mathematical model was determined to be the variable with the most influence on accuracy. Moreover, the results suggest that the use of 10-16 GCPs is sufficient. Additional points do not improve the DEM accuracy or may even worsen it in certain cases. Although the study is carried out in a coastal zone, which restricts the GCPs’ distribution possibilities, the results are comparable with similar results from inland areas.This study has been carried out in the framework of the “Financial aid for the consolidation and structure of competitive units of investigation in the universities of the University Galician System (2016-18)” Ref. ED431B 2016/030. This work has been also supported in the same program by Ref. ED341D R2016/023S

A hybrid photogrammetry approach for archaeological sites: Block alignment issues in a case study (the Roman camp of A Cidadela)

This is the accepted manuscript of the following article: Arza-García, M., Gil-Docampo, M., & Ortiz-Sanz, J. (2019). A hybrid photogrammetry approach for archaeological sites: Block alignment issues in a case study (the Roman camp of A Cidadela). Journal Of Cultural Heritage. doi: 10.1016/j.culher.2019.01.001Photogrammetry is a cost-effective and versatile technique used for the threedimensional (3D) registration of archaeological heritage sites. Managing datasets of heterogeneous images in terms of camera type, elevation platform, position or acquisition time can now be addressed by structure from motion (SfM) software via bundle adjustment in a single block based on collinearity principles. This development enables new possibilities with regard to data completeness assurance for 3D documentation, even for complex sites with occlusive elements and hidden areas. However, hybrid photogrammetry in large datasets often requires multiple photogrammetric blocks that must be processed individually and subsequently aligned to obtain a unified point cloud. In this paper, we discuss the steps required to homogenize the information and the methods used to perform block alignment in these cases. A case study of low-altitude aerial photogrammetry with several cameras and platforms is presented for the Roman camp of A Cidadela in NW Spain as a representative example of an archaeological site that is difficult to survey using a single photogrammetric platform. The relatively large expanse of the area and the fact that it is partially covered by a protective structure constitute an ideal framework for the fusion of multiplatform imagery. The most accurate digital surface model (DSM) was obtained via point-based method fusion, during which subsets are aligned based on automatically extracted tie points (TPs) between the dense point clouds; however, point-based method fusion is very time consuming. When hardware capabilities allow, conducting the process in a single block is preferable, which is a noticeably more accurate procedure than independent block fusionThe study was supported by Xunta de Galicia under the "Financial aid for the consolidation and structure of competitive units of investigation in the universities of the University Galician System (2016-18)" grant Ref. ED431B 2016/030 and Ref. ED341D R2016/023. The authors thank all project partners and collaborators. We would especially like to thank Dr. Santiago Martínez, PhD, for the technical support and IRIS UAV Services S.L. for conducting the flightS

DEM shading method for the correction of pseudoscopic effect on multi-platform satellite imagery

This is an Accepted Manuscript of an article published by Taylor & Francis in GIScience & Remote Sensing on 2014, available online: http://www.tandfonline.com/10.1080/15481603.2014.988433The pseudoscopic effect in satellite imagery causes perception problems for rugged terrain. The topographic relief is perceived in reverse in images with southeast illumination because of the position of land shadows and the mechanisms of human vision and depth perception. This article presents a correction method for false topographic perception phenomena. Superposition of the orthoimage and the correctly shaded digital elevation model (DEM) provides the correct three-dimensional visualization of the relief. This study demonstrates the applicability of this processing technique for the correction of such effects to provide cartography with a more useful interpretation. The resolution of the DEM employed should be in accordance with the spatial resolution of each image. The opacity level proposed for the overlapping DEM is 50%, 30% and 45% for each image type. The selection of the most appropriate local incidence angle is determined by the level of terrain roughness in the work areaWe want to thank the Galician Territorial Information System (SITGA) for the images and the cartographic material provided for the realization of this workS

Virtual Globes for UAV-based data integration: Sputnik GIS and Google Earth™ applications

“This is an Accepted Manuscript of an article published by Taylor & Francis in International Journal of Digital Earth on 03 May 2018, available online: https://www.tandfonline.com/doi/abs/10.1080/17538947.2018.1470205"The integration of local measurements and monitoring via global-scale Earth observations has become a new challenge in digital Earth science. The increasing accessibility and ease of use of virtual globes (VGs) represent primary advantages of this integration, and the digital Earth scientific community has adopted this technology as one of the main methods for disseminating the results of scientific studies. In this study, the best VG software for the dissemination and analysis of high-resolution UAV (Unmanned Aerial Vehicle) data is identified for global and continuous geographic scope support. The VGs Google Earth and Sputnik Geographic Information System (GIS) are selected and compared for this purpose. Google Earth is a free platform and one of the most widely used VGs, and one of its best features its ability to provide users with quality visual results. The proprietary software Sputnik GIS more closely approximates the analytical capacity of a traditional GIS and provides outstanding advantages, such as DEM overlapping and visualization for its disseminationThis work was supported by Xunta de Galicia under the Grant “Financial aid for the consolidation and structure of competitive units of investigation in the universities of the University Galician System (2016-18)” (Ref. ED431B 2016/030 and Ref. ED341D R2016/023). The authors also acknowledge support provided by “Realización de vuelos virtuales en las parcelas del proyecto Green deserts LIFE09 / ENV/ES / 000447”S

IR Thermography from UAVs to Monitor Thermal Anomalies in the Envelopes of Traditional Wine Cellars: Field Test

Infrared thermography (IRT) techniques for building inspection are currently becoming increasingly popular as non-destructive methods that provide valuable information about surface temperature (ST) and ST contrast (delta-T). With the advent of unmanned aerial vehicle (UAV)-mounted thermal cameras, IRT technology is now endowed with improved flexibility from an aerial perspective for the study of building envelopes. A case study cellar in Northwest (NW) Spain is used to assess the capability and reliability of low-altitude passive IRT in evaluating a typical semi-buried building. The study comparatively assesses the use of a pole-mounted FLIR B335 camera and a drone-mounted FLIR Vue Pro R camera for this purpose. Both tested IRT systems demonstrate good e ectiveness in detecting thermal anomalies (e.g., thermal bridges, air leakages, constructive singularities, and moisture in the walls of the cellar) but pose some di culties in performing accurate ST measurements under real operating conditions. Working with UAVs gives great flexibility for the inspection, but the angle of view strongly influences the radiometric data captured and must be taken into account to avoid disturbances due to specular reflections.This work was supported by the Spanish Ministry of Science, Innovation and Universities under the National Programme for Research Aimed at the Challenges of Society grant for the project “Bioclimatic Design Strategies in Wine Cellars as Nearly Zero-Energy Building Models” [BIA2014-54291-R]S

The Future Professionals in Geomatics

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A World Wide Web-Based Practice That Disseminates Photogrammetry. Inspiring secondary students to pursue geomatics careers

This is the accepted version of a manuscript published in IEEE Geoscience and Remote Sensing Magazine. ISSN: 2168-6831. https://doi.org/10.1109/MGRS.2018.2876565The D3MOBILE Metrology World League was established in 2013 with the aim of encouraging curiosity and interest in science, and particularly geoscience, in the secondary students of grades ISCED 1 and 2. Presented as an international championship, D3MOBILE introduces students to the discipline of photogrammetry through the e-learning methodology concept. The use of well-known technologies by the pupils, such as their own mobile devices (smartphones or tablets), allows us to develop educational procedures that are attractive and challenging for them. All the work that we propose for the participants is presented in a scientific, technical, and professional language but in a more interactive format than traditional textbooks or theoretical classes. The proposed challenges provide students with the opportunity to establish their own learning objectives, work as a team and take responsibility for their work. This paper addresses the experience, from an educational perspective, carried out by our research group CIGEO (Civil Engineering and Geomatics) during the organization of the first five editions of this international “concept submission competition”. During this period, we tried to create and improve a project-based learning (PBL) methodology that can be adapted to e-learning and daily classwork at the high school level, which can be easily implemented regardless of the number of participants and can be implemented anywhere in the world. The obtained results demonstrate the potential of alternative teaching methods combined with new technologies to engage students in science learning and improve the perception of the geosciences as a job opportunityWe thankfully acknowledge the financial support from FECYT—Ministerio de Economía y Competitividad (FCT 12-3495; FCT 13-5961; FCT 14-8038; FCT 15-9481); and Xunta de Galicia (ED431B22016/030; ED341DR2016/023). We would also like to thank our large number of sponsors and collaborators: Universia, BQ, Autodesk, National Geographic Institute (IGN), City Council of Lugo, Provincial Council of Lugo, Spanish Center of Metrology (CEM), Fundación Vodafone, CEAPA, City Council of La Coruña, Fundación Barrié, ANPE, CSI-F, Fundación Comforp, PCE, Univ. Tecnológica Nacional (Argentina), Fundacion Mujeres, EDUCACION 3.0. and likely even more entities. Finally, we would like to thank the schoolteachers and students whose work and dedication allowed this project to achieve its objectivesS

Above-ground biomass estimation of arable crops using UAV-based SfM photogrammetry

This is an Accepted Manuscript of an article published by Taylor & Francis in Geocarto International on 3 dec 2018, available online: http://www.tandfonline.com/10.1080/10106049.2018.1552322Methods of estimating the total amount of above-ground biomass (AGB) in crop fields are generally based on labourious, random, and destructive in situ sampling. This study proposes a methodology for estimating herbaceous crop biomass using conventional optical cameras and structure from motion (SfM) photogrammetry. The proposed method is based on the determination of volumes according to the difference between a digital terrain model (DTM) and digital surface model (DSM) of vegetative cover. A density factor was calibrated based on a subset of destructive random samples to relate the volume and biomass and efficiently quantify the total AGB. In all cases, RMSE Z values less than 0.23 m were obtained for the DTMDSM coupling. Biomass field data confirmed the goodness of fit of the yieldbiomass estimation (R2=0,88 and 1,12 kg/ha) mainly in plots with uniform vegetation coverage. Furthermore, the method was demonstrated to be scalable to multiple platform types and sensorsThis work was supported by the life project “Operation CO2: Integrated Agroforestry Practices and Nature Conservation Against Climate Change - LIFE+ 11 ENV/ES/535” and by Xunta de Galicia under the grant “Financial aid for the consolidation and structure of competitive units of investigation in the universities of the University Galician System (2016-18)” Ref. ED431B 2016/030 and Ref. ED341D R2016/023.S

Plant survival monitoring with UAVs and multispectral data in difficult access afforested areas

This is an Accepted Manuscript of an article published by Taylor & Francis in Geocarto International on 02 Oct 2018, available online: http://www.tandfonline.com/10.1080/10106049.2018.1508312Water supply devices enable afforestation in dry climates and on poor lands with generally high success rates. Previous survival analyses have been based on the direct observation of each individual plant in the field, which entails considerable effort and costs. This study provides a low-cost method to discriminate between live and dead plants in afforestations that can efficiently replace traditional field inspections through the use of UAVs equipped with RGB and NIR sensors. The method combines the use of a conventional camera with an identical camera modified to record the NIR channel. Survival analysis was performed with digital image processing techniques based on calculated indices associated with plant vigour and PCA-based decorrelation. The method yielded results with high global accuracy rates (~96.2%) with a minimum percentage of doubtful plants, even in young plantations (seedlings < 30 cm tall). The procedure could be particularly useful in hazardous areasThis work was supported by the Xunta de Galicia under the Grant “Financial aid for the consolidation and structure of competitive units of investigation in the universities of the University Galician System (2016-18)” [ED431B 2016/030, ED341D R2016/023] and the European Program Life+ [LIFE/ENV/ES/000447] “The Green Deserts: New planting techniques for tree cultivation in desertified environments to face Climate Change”.S

A PBeL for training non-experts in mobile-based photogrammetry and accurate 3-D recording of small-size/non-complex objects

The high level of automation, user-friendliness and cost-effectiveness of photogrammetry have contributed significantly to its popularisation among amateur users in recent years. Paradoxically, this situation poses challenges when relying on the accuracy of the derived 3-D products requiring control procedures to be implemented. In this context, we present a case study of the D3Mobile project: a fully online competition for participants worldwide funded by the International Society of Photogrammetry and Remote Sensing (ISPRS). The aim is for participants to obtain reality-based 3-D models using their own mobile phones and to critically examine the metric accuracy that hides behind the beguiling realism of photogrammetry. The relative precision of the former participants’ models reached values around 1:2,000, proportionally to the object size. These results provide an idea of the current level of development of photogrammetry and the potential it offers for any kind of user after proper capacity building and trainingS