Classification of airborne laser scanning point clouds based on binomial logistic regression analysis

This article presents a newly developed procedure for the classification of airborne laser scanning (ALS) point clouds, based on binomial logistic regression analysis. By using a feature space containing a large number of adaptable geometrical parameters, this new procedure can be applied to point clouds covering different types of topography and variable point densities. Besides, the procedure can be adapted to different user requirements. A binomial logistic model is estimated for all a priori defined classes, using a training set of manually classified points. For each point, a value is calculated defining the probability that this point belongs to a certain class. The class with the highest probability will be used for the final point classification. Besides, the use of statistical methods enables a thorough model evaluation by the implementation of well-founded inference criteria. If necessary, the interpretation of these inference analyses also enables the possible definition of more sub-classes. The use of a large number of geometrical parameters is an important advantage of this procedure in comparison with current classification algorithms. It allows more user modifications for the large variety of types of ALS point clouds, while still achieving comparable classification results. It is indeed possible to evaluate parameters as degrees of freedom and remove or add parameters as a function of the type of study area. The performance of this procedure is successfully demonstrated by classifying two different ALS point sets from an urban and a rural area. Moreover, the potential of the proposed classification procedure is explored for terrestrial data

Airborne Laser Scanning (ALS) point cloud ground filtering for area of an active landslide (Doren, Western Austria)

Ground filtering of point cloud is the primary step required for Digital Terrain Model (DTM) generation. The procedure is especially interesting for forested areas, since LiDAR systems can measure terrain elevation under vegetation cover with a high level of penetration. This work analyzes the potential of ALS data ground filtering for area of an active landslide. The results of ALS filtering, for example, may improve geomorphological and motiondetection studies. ALS data was collected during flight campaign 2011 under leaf-off conditions for Doren region, Vorarlberg, Western Austria. In this area, non-ground objects are mostly low vegetation such as shrubs, small trees etc. The vegetation is more dense in lower part of the landslide where erosion is smaller. Vegetation points can be removed based on the hypothesis that these are significantly higher than their neighboring points. However, in case of steep terrain, ground points may have the same heights as vegetation points, and thus, local slope should be considered. Also, if terrain roughness increases, the classification may become even more complex. Software system OPALS (Orientation and Processing of Airborne Laser Scanning data, Vienna University of Technology) was used for processing the ALS data. Labeling ground points has been made using physical and geometrical attributes (parameters) of ALS points. Also additional attributes were calculated in order to improve extraction. Since bare ground surface is usually smooth and continuous unlike vegetation, standard deviation of local elevations was used as roughness measure to differentiate these surfaces. EchoRatio (ER) was adopted as a measure of surface penetrability, while number of echoes and differentiation between echoes (EchoNumber) were also deployed in filtering. Since the ground points are measurements from bare-earth that are usually the lowest surface features in a local area, normalized height was defined as a rank of neighboring points. Additionally, a so-called openness parameter was used as a convexity/concavity measure of surface. All of the mentioned point attributes have been combined in a decision tree in order to extract bare ground points. Based on a preliminary analysis, it is noted that implemented filtering procedure has difficulties with surfaces with rough terrain or steep relief. There is an assumption for lack of ground points in areas with dense vegetation that reduced the penetration of laser beams to the ground (lower part of a landslide). Also, points representing low vegetation were often labeled as ground points. Procedure produced holes in point cloud which demanded appropriate interpolation methods to be applied.Geophysical Research Abstract

Airborne Laser Scanning (ALS) point cloud ground filtering for area of an active landslide (Doren, Western Austria)

Ground filtering of point cloud is the primary step required for Digital Terrain Model (DTM) generation. The procedure is especially interesting for forested areas, since LiDAR systems can measure terrain elevation under vegetation cover with a high level of penetration. This work analyzes the potential of ALS data ground filtering for area of an active landslide. The results of ALS filtering, for example, may improve geomorphological and motiondetection studies. ALS data was collected during flight campaign 2011 under leaf-off conditions for Doren region, Vorarlberg, Western Austria. In this area, non-ground objects are mostly low vegetation such as shrubs, small trees etc. The vegetation is more dense in lower part of the landslide where erosion is smaller. Vegetation points can be removed based on the hypothesis that these are significantly higher than their neighboring points. However, in case of steep terrain, ground points may have the same heights as vegetation points, and thus, local slope should be considered. Also, if terrain roughness increases, the classification may become even more complex. Software system OPALS (Orientation and Processing of Airborne Laser Scanning data, Vienna University of Technology) was used for processing the ALS data. Labeling ground points has been made using physical and geometrical attributes (parameters) of ALS points. Also additional attributes were calculated in order to improve extraction. Since bare ground surface is usually smooth and continuous unlike vegetation, standard deviation of local elevations was used as roughness measure to differentiate these surfaces. EchoRatio (ER) was adopted as a measure of surface penetrability, while number of echoes and differentiation between echoes (EchoNumber) were also deployed in filtering. Since the ground points are measurements from bare-earth that are usually the lowest surface features in a local area, normalized height was defined as a rank of neighboring points. Additionally, a so-called openness parameter was used as a convexity/concavity measure of surface. All of the mentioned point attributes have been combined in a decision tree in order to extract bare ground points. Based on a preliminary analysis, it is noted that implemented filtering procedure has difficulties with surfaces with rough terrain or steep relief. There is an assumption for lack of ground points in areas with dense vegetation that reduced the penetration of laser beams to the ground (lower part of a landslide). Also, points representing low vegetation were often labeled as ground points. Procedure produced holes in point cloud which demanded appropriate interpolation methods to be applied.Geophysical Research Abstract

Vorwort und Editorial

Auch wenn (berufs-)bildungspolitische Diskussionen um Gleichwertigkeit, Durchlässigkeit, Anerkennung und aktuell um Verberuflichung des Akademischen und Akademisierung des Beruflichen eine Annäherung allgemeiner und beruflicher Bildung vermuten lassen, ist die Frage nach dem Verhältnis dieser beiden Bildungen nicht eindeutig gelöst. Vielmehr stehen nach wie vor unterschiedliche Positionen nebeneinander. Im folgenden Beitrag geht es weniger um die Frage danach, was beide Bildungen eint, trennt und wie sie miteinander verbunden werden können. Vielmehr soll sich der Frage angenähert werden, von welchen übergreifenden historischen bildungstheoretischen und -politischen Gedanken und Ereignissen beide Bereiche betroffen waren und sind, und wie diese die Verhältnisfrage tangiert und entschieden haben. Unter drei historisch widersprüchlichen Aspekten, von denen sowohl die allgemeine als auch die berufliche Bildung betroffen sind, wird thematisiert, wie diese Widersprüche intern, also im Verhältnis zwischen Allgemeinbildung und Berufsbildung als Idee und allgemeiner und beruflicher Bildung als soziale Realität historisch gelöst wurden. Zu diesen übergreifenden Widersprüchen gehören: Bildung für alle und die soziale Portionierung von Bildung, Allseitigkeit von Bildung und Halbbildung und allgemeine Nützlichkeit von Bildung und Ökonomisierung. Die Frage, die mit diesem Beitrag angestoßen werden soll, ist, wie über Bildung übergreifend nachgedacht werden kann, damit allgemeine und berufliche Bildung nicht mehr gegeneinander ausgespielt werden und ohne Ungleichwertigkeiten ineinanderfließen, sich abgrenzen und ergänzen können

A topographic Mars information system : concepts for management, analysis and visualization of planet-wide data

Zsfassung in dt. SpracheAn Bord der Sonde Mars Express befindet sich das hochauflösende Kamerasystem High Resolution Stereo Camera (HRSC). Zur effizienten Verwaltung der erwarteten Bilddaten gemeinsam mit topographischen Daten sowohl als Originalpunktwolken wie auch davon abgeleiteter Geländemodelle, wurde ein Topographisches Mars Informationssystem (TMIS) konzipiert und entwickelt.Im ersten Teil der Arbeit werden Konzepte zur Modellierung und Verwaltung räumlicher Daten unter Berücksichtigung vorhandener Standards und Normen beschrieben. Die Möglichkeiten auf Extensible Markup Language (XML) basierten Formaten für Datenhaltung und Datenaustausch raumbezogener Daten sowie für deren kartographische Aufbereitung zur Darstellung im Internet werden im Detail untersucht. Derzeitig verfügbare Implementierungen von Web Map Services (WMS) liefern meist statische Kartendarstellungen, obwohl seitens der Spezifikation von WMS auch objekt-basierte Ausgabeformate wie z.B. Scalable Vector Graphics (SVG) unterstützt werden. Im Rahmen der Entwicklung einer kartenbasierten Benutzerschnittstelle für TMIS wurden die Möglichkeiten von SVG eingehend untersucht. Basierend auf den resultierenden Erkenntnissen werden mögliche Erweiterungen zur Verbesserung der Anwendbarkeit vorhandener XML basierter Formate im Bereich der Geodatenmodellierung und -verwaltung präsentiert. Abschließend wird der gegenwärtige Implementierungsstand von TMIS als Anwendungsbeispiel der beschriebenen Methoden gezeigt.Im zweiten Teil der Arbeit werden Methoden zur Bearbeitung und Analyse topographischer Marsdaten untersucht. Als Testdatensatz dienten Bild- und Topographiedaten welche im Rahmen der NASA Mission Mars Global Surveyor (MGS) erfasst wurden. Zunächst wird eine Methode zur Detektion und anschließenden Elimination grober Datenfehler, welche in den Originalpunkten enthalten sind, vorgestellt. Die Ableitung homogener und von zufälligen Fehlern bereinigter DGMe als Grundlage für weiterführende Analysen wir ebenfalls näher beschrieben. Seit die Oberfläche des Mars erkundet wird drängt sich die Frage auf, ob es in früheren Zeiten Oberflächenwasser gab. Um der Beantwortung dieser Frage näher zu kommen, wurden rasterbasierte, hydrologische Analysemethoden an ausgewählten, möglicherweise durch Oberflächenwasser geformten Bereichen des Mars angewandt und die Ergebnisse visuell aufbereitet. Als Abschluss der Arbeit werden dreidimensionale Visualisierungen dieser Resultate, unter anderem zur Darstellung im Internet, präsentiert.The High Resolution Stereo Camera (HRSC) is aboard the spacecraft Mars Express. Task of the Topographic Mars Information System (TMIS) is an efficient management of the expected image data, and also of surface point data as derived from these images using feature-based image matching methods, as well as subsequently derived digital terrain models (DTM).The first part of this thesis deals with concepts of spatial data modeling and management and with data formats and data exchange with respect to available standards, mostly based on the Extensible Markup Language (XML). Special attention is paid to the Geography Markup Language for data representation and exchange and to Scalable Vector Graphics for web presentation of spatial data. Web presentation formats based on static images provided by a Web Map Service are compared to object-based presentation formats. Further on, shortcomings as well as possible improvements and extensions to enhance the capability for efficient application of XML and related technologies in the area of geodata management are presented. Finally, the realization of the TMIS framework is described.In the second part, methods for topographic data manipulation and analysis are investigated. For testing purposes, image and topographic data acquired by the NASA probe Mars Global Surveyor has been used.Since the original surface point cloud contained gross, a method to detect and eliminate the erroneous points became essential. The computation of DTMs for further analysis is described afterwards. Ever since the surface of Mars is investigated in detail, scientists are discussing if liquid surface water was involved in the surface forming process in former times. To help answering this question, raster-based hydrological analysis methods were applied to regions which were possibly formed by water. The results are prepared for visual presentation. Finally, 3D visualizations of these results, e.g. for web presentation, are provided.11

A Comprehensive Automated 3D Approach for Building Extraction, Reconstruction, and Regularization from Airborne Laser Scanning Point Clouds

Three dimensional city models are necessary for supporting numerous management applications. For the determination of city models for visualization purposes, several standardized workflows do exist. They are either based on photogrammetry or on LiDAR or on a combination of both data acquisition techniques. However, the automated determination of reliable and highly accurate city models is still a challenging task, requiring a workflow comprising several processing steps. The most relevant are building detection, building outline generation, building modeling, and finally, building quality analysis. Commercial software tools for building modeling require, generally, a high degree of human interaction and most automated approaches described in literature stress the steps of such a workflow individually. In this article, we propose a comprehensive approach for automated determination of 3D city models from airborne acquired point cloud data. It is based on the assumption that individual buildings can be modeled properly by a composition of a set of planar faces. Hence, it is based on a reliable 3D segmentation algorithm, detecting planar faces in a point cloud. This segmentation is of crucial importance for the outline detection and for the modeling approach. We describe the theoretical background, the segmentation algorithm, the outline detection, and the modeling approach, and we present and discuss several actual projects

Digital surface model, hillshade and orthophoto of the world's largest fossil oyster reef, links to GeoTIFFs

The world's largest fossil oyster reef, formed by the giant oyster Crassostrea gryphoides and located in Stetten (north of Vienna, Austria) is studied by Harzhauser et al., 2015, 2016; Djuricic et al., 2016. Digital documentation of the unique geological site is provided by terrestrial laser scanning (TLS) at the millimeter scale. Obtaining meaningful results is not merely a matter of data acquisition with a suitable device; it requires proper planning, data management, and postprocessing. Terrestrial laser scanning technology has a high potential for providing precise 3D mapping that serves as the basis for automatic object detection in different scenarios; however, it faces challenges in the presence of large amounts of data and the irregular geometry of an oyster reef. We provide a detailed description of the techniques and strategy used for data collection and processing in Djuricic et al., 2016. The use of laser scanning provided the ability to measure surface points of 46,840 (estimated) shells. They are up to 60-cm-long oyster specimens, and their surfaces are modeled with a high accuracy of 1 mm. In addition to laser scanning measurements, more than 300 photographs were captured, and an orthophoto mosaic was generated with a ground sampling distance (GSD) of 0.5 mm. This high-resolution 3D information and the photographic texture serve as the basis for ongoing and future geological and paleontological analyses. Moreover, they provide unprecedented documentation for conservation issues at a unique natural heritage site