A novel GIS method to determine an urban centrality index applied to the Barcelona metropolitan area

Events occurring in a city, such as car accidents, attacks on the security or activities locations are channelled in the urban network. The goal of this report is to provide a GIS tool able to compute densities and diversities in a network space rather than in the euclidean one. The network space created to support these calculations is a shortest path tree for a given bandwith. On the basis of this shortest path tree, three parameters are calculated: the density and the diversity of activities and the density of edges. The case study of this report is the city of Barcelona. The activities of this city were projected on the network. Indeed, activities like other events in the urban space tend to follow the network. The Human Space Lab (HSL) of the Politecnico di Milano (IT) has applied its Multiple Centrality Assessment to Barcelona's network. Thus, edges become a value of centrality. The network density of the edges presented in this report will take into account these attributes such as the value of population used in other available GIS density tools. The further idea, is to weigh the events (activities or edges) by their distances, as in a standard kernel density estimation. The network approach reveals a spatial distribution of the values sensitive to the favourite direction of the network. The diversity measured along the network make out particular area of the city as residential or commercial zones

Urban monitoring using NetKDE and VGI: network based kernel density estimation on volunteered geographic information applied to Baghdad, Iraq

This paper presents a methodology for urban monitoring using volunteered geographic information (VGI) and journalism data Iraq war logs with network based kernel density estimation (NetKDE). It investigates, using spatio-temporal analysis, the evolution of urban events in Baghdad between 2004 and 2009. The extracted street network is based on the data distributed by OpenStreetMap (OSM). A total of 21,876 logged events, 66,648 network segments, 22,644 gridpoints (200m resolution grid) and 362,304 gridpoints (50m resolution grid) are used for the analysis. The methodology combines and adapts these VGI data and is mainly based on open source and/or publicly available software. It handles very large datasets with multiscale, multi-resolution and temporal perspectives. Fuzzy-set map comparison (FMC) is used to identify level of changes between each period of time. The methodology is already used in other fields of research being biology, urban planning, criminology or economic evelopment. It should help stakeholders in respective domain to analyze the evolution of network constrained events in multiple contexts. This paper is divided in three parts. Firstly, conceptual background of VGI, NetKDE and FMC is presented. Secondly, the methodology is illustrated using data Iraq war logs, OSM data and grids with two different resolutions. Thirdly, spatio-temporal analysis results are presented and discussed.Peer Reviewe

Crowdsourcing the georeferencing of historical pictures

Countless organizations own archive pictures which are not used due to the difficulty of localizing them. Only the participation of volunteers can help to identify the image content. Through an accessible web interface called smapshot, citizens are able to georeference historical images without any prior specific competence. To avoid the volunteers to face the complexity of 3D digitization and navigation, we implemented a state of the art photogrammetry camera orientation algorithm in the platform. Currently several thousand images from all around Switzerland have been georeferenced by the crowd. At this time the tool is mainly used by the population for the visualization experience and the nostalgia behind it. The ambition is to support scientists to analyze landscape evolution

Challenges in VGI for scientific projects

Volunteered Geographic Information (VGI) is a recent trend that has been successfully used in order to collect and share geographic information. This method is of interest for scientists who are in need of data and who want to get people involved in their cause. In this paper we discuss the challenges and opportunities that scientists may face when using the concept. An initial challenge is to find users who are willing to contribute. Second scientist must get these users to interact with the application and with each other. The final goal is to end up with high quality data that can be used for scientific research

Registration of single landscape photographs with 3D landscape models

Terrestrial imagery found in public databases is an alternative and complementary data source for environmental studies. Compared to usual data source, such as airborne images, terrestrial pictures may have higher temporal and spatial resolutions. They are especially valuable in studying the past, when airborne acquisitions were more rare or inexistent. Nevertheless, terrestrial image databases are typically imperfectly georeferenced, if at all. Hence, it is difficult to retrieve images of interest in a database. Moreover, georeferencing processes proposed for these images are either totally manual or rely on the existence of a collection of similar and overlapping images. The first is time-consuming and the second is appropriate only for particular sets of images. An alternative and more general georeferencing procedure is the registration of a picture with a landscape model. In this thesis, we propose to use as the reference a 3D virtual globe and our aim is to retrieve the orientation and the location of the camera. The location and orientation of a picture can be computed with correspondences that a user recognizes and clicks in a picture and in an orthoimage. However, these two distinct types of images are difficult to match because of the distortions resulting from the different viewpoints. Hence, we provide a navigation tool to scroll through a 3D model to ease this task. Indeed, to find the orientation of a picture, users typically exploit the skyline which appears only in a 3D view. In imitation, we develop a novel skyline-matching technique, based on Dynamic Time Warping, to compute the fine orientation of a picture. In a second phase, we assess whether the similarities between a 3D synthetic image and real images can be used to compute the orientation of a picture. The matching of real images with a model is challenging. We show how images shared on the web can be inserted in the landscape model to ease the georeferencing. Finally, all of the presented pose estimation schemes assume that every location of the map is as likely to be a shooting spot. However, we show that geographic indicators related to accessibility and morphology are correlated with a database of picture locations. Exploiting these relations, our last contribution is a map of the attractiveness. In this thesis, we observed that pose estimation from the automatic registration of a real image with a landscape model cannot compete with the accuracy reached by an operator or a standard photogrammetric workflow. However, the proposed methods can greatly reduce the operator workload for the manual georeferencing by finding automatically correspondences with a 3D landscape model. Second, they are a valid alternative if the required conditions for Structure-from-Motion are not respected. Finally, the accuracy obtained is sufficient to explore image databases with spatial queries and to add geographic information in the pictures. Registration of landscape images with landscape models has previously received limited attention. The tools developed in this thesis can ease the work of archivists (in the management and provision of efficient image databases), environmental scientists (for the extraction of georeferenced information from pictures) and the general public (to browse collections of augmented images inserted in a virtual globe)

sMapShot ::Georeferenzierung historischer Landschaftsbilder durch Crowdsourcing

Historische Landschaftsbilder haben einen hohen historischen und geografischen Wert. Sie enthalten genaue Informationen über Landschaftsveränderungen und sind eine wertvolle Informationsquelle für Raum- und Stadtplaner, Geographen und Historiker. Grosse Mengen von historischen Landschaftschaftsbildern sammeln derzeit Staub in vielen Archiven der Schweiz. Des weiteren fehlen effiziente Suchmaschinen in Bildarchiven, welche schon Landschaftsbilder digitalisiert haben. Ein Grund dafür ist, dass die Bilder nicht georeferenziert sind oder nur grob nach einem Ortsnamen, der in den Metadaten des Bildes vorkommt, katalogisiert sind. In unserem Projekt wollen wir das geographische Wissen von freiwilligen Teilnehmern nutzen, um die genaue 3D-Georeferenzierung von historischen Bildern herauszufinden. Diese Georeferenzierung wird dann verwendet, um einen virtuellen Globus der Vergangenheit aufzubauen und um die genauen Ortsnamen zu berechnen, die im Bild sichtbar ist

3D georeferencing of historical photos by volunteers ::selected papers of the 21st AGILE Conference on Geographic Information Science

Historical photographs are a very rich source of information that can be useful in a variety of different contexts such as environmental analyses, land planning and illustration of landscape evolution. However to reach this goal the images must be accurately georeferenced. In this paper we propose to use the crowd to perform the 3D georeferencing of collections of historical images. To this goal we implemented a web 3D georeferencer that offers volunteers the possibility to semiautomatically identify 1. the location of the point from where a picture has been taken, 2. the three angles: tilt, roll and yaw and 3. the field of view. A virtual webbased globe is the central element in this tool that allows both for the georeferencing in three dimensions by volunteers and for the visualization of georeferenced images to assess the landscape variation through time. In this paper we evaluate the method and the georeferencer and give suggestions for further developments and exploitation of the database

A semi-automatic tool to georeference historical landscape images

Smapshot is a web-based participatory virtual globe where users can georeference historical images of the landscape by clicking a minimum of six well identifiable correspondence points between the image and a 3D virtual globe. The images database is expected to grow exponentially. In a near future, the work of the web users will no longer be enough. To tackle this issue, we developed a semi-automatic process to georeference images. The volunteers will be shown only images having a maximum number of neighbour images in the matching graph. These neighbour images are the ones with which they share some overlay. This overlap is detected using the SIFT algorithm in a pairewise matching process. For an image pair made of a reference image with a known pose and a query image we want to georeference, we extracted the 3D world coordinates of the tie points from a digital elevation model. Then, by running a perspective-n-point algorithm after having geometrically tested the resulting homography between the two images, we compute the 6 degree of freedom pose, i.e. the position (X,Y,Z) and orientation (azimuth, tilt and roll angles) of the query image. The query image then becomes a reference and the georeference computation can be propagated more deeply in the graph structure