Abstract:In this paper we present a stereo feature-based method using SIFT (Scale-invariant feature transform) descriptors. We use automatic feature extractors, matching algorithms between images and techniques of robust estimation to produce a DTM (Digital Terrain Model) using convergent shots of a rock glacier.The geomorphologic structure observed in this study is the Veleta rock glacier (Sierra Nevada, Granada, Spain). This rock glacier is of high scientific interest because it is the southernmost active rock glacier in Europe and it has been analyzed every year since 2001. The research on the Veleta rock glacier is devoted to the study of its displacement and cartography through geodetic and photogrammetric techniques.

At present there is a wide variety of geomatic techniques available to determine the dynamics of glaciers, rock glaciers and ice patches. Between 1991 and 2012, different geomatic techniques – total station, global positioning system, close‐range photogrammetry and terrestrial laser scanner – were applied to monitor the movement of cryosphere landforms in the high mountains of the Iberian Peninsula. The applied techniques must be adapted to the dynamic conditions of cryospheric environments, and so there is no ideal general technique, and depending on the characteristics of the geomorphological structure to be studied, different geomatic techniques can be used. However, there are situations in which certain instruments cannot be used: global positioning system–real time kinematics shows difficulties when the presence of vertical walls cause a ‘multipath’ effect. The technique that provides the best results in each case must be chosen, although they can all give good results in measuring and monitoring geomorphological processes. This paper analyses the techniques used and results on vertical and horizontal changes of glaciers, rock glaciers and ice patches in the Sierra Nevada, Pyrenees and Picos de Europa, and differences among them by location and topoclimatic setting. All glaciers and rock glaciers show a thinning tendency and annual variations in the flow velocity. In addition to the specific dynamic analysis, the geomatic techniques can be used to detail scale and volume changes and perimeter of the analysed landforms.

ABSTRACT:The conservation of built heritage is becoming increasingly important, and may even be an obligation for future generations. Techniques must therefore be developed to help document heritage and thus improve knowledge and conservation. The terrestrial laser scanning technique allows a massive capture of points of an object. Among its main applications are to obtain geometries of historic buildings and monuments, allowing the documentation of their heritage. But this technique also facilitates other very important information for the conservation of the monument in question from the same data set: the damage it presents. We can, therefore, also document the geometry of the object by making a survey of the damage it presents at the moment of data collection. The cracks and their layout and trajectory can be observed, allowing measurements to be made to assess necessary conservation measures. Given that the apertures of the same crack at different points in historical structures often vary by several centimeters, it is also important to know the extent of the damage along its entire path, and whether there is any relative motion between the two sides of the crack. This communication presents the application of laser scanning in the Alcántara Bridge and Coria Cathedral, both in the province of Cáceres (Spain). It outlines the criteria used for scanning both monuments: selection of placements, recording technique, errors between placements and the elimination of residual points. Once the mesh had been obtained, the information on the damage presented by these monuments was analysed, describing, characterizing and contrasting them with data taken in the field. * Corresponding author. This is useful to know for communication with the appropriate person in cases with more than one author.

En este trabajo se evalúan los métodos de foto-reconstrucción automatizada basados en el uso conjunto de las técnicas Structure from Motion (SfM) y Multi-View Stereo (MVS) para medir, monitorizar y cuantificar la dinámica de tres formas geomorfológicas: i) el glaciar rocoso del Corral del Veleta (Granada, España), ii) un paisaje de cárcavas de tipo calanchi (Sicilia, Italia) y ii) cinco pequeñas cabeceras de cárcava (Cáceres, España). Se incluyen en este trabajo los resultados sobre la precisión, utilidad y aplicabilidad de estas técnicas. Para la cuantificación de la precisión se utilizan el error cuadrático medio (RMSE) de los puntos de control que se emplean en la georreferenciación y las distancias medias absolutas entre cada nube de puntos y una nube de puntos de referencia calculadas con los métodos cloud-to-cloud y multiscale model-to-model cloud comparison. Para los casos i) y iii) las nubes de referencia se capturaron utilizando un escáner láser terrestre, mientras que para el caso ii) se empleó un modelo digital de elevaciones obtenido mediante fotogrametría clásica aplicada a fotogramas aéreos capturados con un vehículo aéreo no tripulado. Los resultados de estos análisis mostraron precisiones de rango centimétrico con distancias medias a los modelos de referencia que oscilaron entre 0,01 m y 0,42 m. Las precisiones estimadas indican que los modelos obtenidos podrían utilizarse para calcular el volumen de cambio geomorfológico, tan sólo en el caso de las cabeceras. En el caso del glaciar y del calanchi los modelos podrían emplearse para elaborar cartografía precisa o estimar parámetros morfológicos, pero no para registrar cambios a escala anual.