In geomorphology, PhotoScan is a software that is used to produce Digital Surface Models (DSMs). It constructs 3D environments from 2D imagery (often taken by Unmanned Aerial Vehicles (UAV)) based on Structure-from-Motion (SfM) and Multi-View Stereo (MVS) principles. However, unpublished computer-vision algorithms used, contain random elements which can affect the accuracy of the outputs. For this letter, ten model runs with identical inputs were performed on UAV imagery of a rock glacier to analyse the magnitude of the variation between the different model outputs. This variation was quantified calculating the standard deviation of each cell value in the respective DSMs and derivatives (curvature). Places with steep slope gradients have considerably more DSM variation (up to 10 cm) but stay within the range of the model's accuracy (10 vertical cm) for 88-96% of the area. The edges of the model also show a larger variability (0.10-3 m), related to a lower number of overlapping images. These results should be accounted for when performing a geomorphological research at centimetre scale using PhotoScan, especially in areas with a complex relief. Using medium-quality runs, additional oblique viewpoints and respecting a minimum of five overlapping images can minimize the software's variations.

Abstract. The goal of this research is to design, use and evaluate a set of weblectures, specifically tailored to the needs of students in higher education who follow GIS-related courses. Since education in GIS includes theoretical concepts and practical experience, these teaching strategies will both be implemented in the weblectures. The User Centered Design approach is used in the design process to increase the acceptance of the weblectures and the motivation to use them: perceived usefulness and ease of use. The results show that the students appreciate the initial set of weblectures, but that they need to be motivated more to use them (especially when theoretical topics are covered). Students still value the 'traditional' face-to-face lectures and see the weblectures as an ideal complement.

Abstract. The destructive nature of archaeological excavations and the spatial character of archaeological finds make 3D models valuable contributions to the documentation of archaeological information. Laser scanning allows highly accurate 3D reconstructions, but involves considerable costs and expert knowledge. Therefore, photo modelling could be considered as a useful alternative. In this paper, we will demonstrate on the one hand the costefficiency and the consequent time-efficiency of the technique and on the other hand its (sub-decimeter) accuracy. Furthermore, the possibilities and advantages of motorized unmanned aerial vehicles (UAV) and helium balloons as airborne platform for image acquisition are shown. For this purpose, a case study is performed at the Mayan archaeological site of Edzna (Mexico). Using the Structure from Motion (SfM) and Multi-View Stereo (MVS) algorithm, terrestrial and aerial photographic recordings are processed into the final 3D models. For the quality assessment the photographic recordings are supplemented with topographic measurements.

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Urban polycentricity has become a key concept in urban and regional studies and is increasingly adopted as an organizational framework for conducting empirical research. Within this literature, polycentric urban regions are commonly defined as territories that have multiple, proximately located (sub)centers and are characterized by balanced urban development. However, analytical‐operational frameworks to identify and classify PURs are often ad hoc efforts to answer a specific research question and underlying work is often shelved rather than shared and/or made accessible. As a result, challenges associated with generalizability, reproducibility, and replicability clearly loom large in the urban polycentricity literature. Against this backdrop, this article describes the discrepancy between a rich debate on polycentricity and the paucity of tools enabling the disambiguation and reproducibility of results claimed by various authors around this polysemic concept. We present an online and open tool—PURban—that brings together the major analytical‐operational frameworks and data sets in urban polycentricity research and allows parametrizing key operational choices. To illustrate the tool, we demonstrate how it facilitates the identification, mapping and analysis of degrees of morphological polycentricity in European urban systems. We conclude by reflecting on how this tool can act as a catalyst for future research on urban polycentricity.