Norbert Haala

Extraction of buildings and trees in urban environments

In this article, two methods for data collection in urban environments are presented. The first method combines multispectral imagery and laser altimeter data in an integrated classification for the extraction of buildings, trees and grass-covered areas. The second approach uses laser data and 2D ground plan information to obtain 3D reconstructions of buildings.

Digital Photogrammetric Camera Evaluation - Generation of Di- gital Elevation Models

Summary: During the implementation of the DGPF-project on Digital Photogrammetric Camera Evaluation a team “Digital Elevation Models” was established. The main goal was to use the test’s framework for documentation and evaluation of the current state-of-the-art on photogrammetric 3D data capture from automatic image matching. During these investigations the accuracy and reliability of DSM rasters and 3D point clouds as derived from imagery of digital photogrammetric camera systems were evaluated. For this purpose they were compared to reference measurements from ground truth and airborne LiDAR. In addition to the evaluation of standard products, the usability of elevation data from image matching was investigated while aiming at specific applications in the context of urban modeling and forestry. Zusammenfassung: Wahrend des DGPF-Projektes zur Evaluierung digitaler photogrammetrischer Luftbildkamerasysteme wurde auch eine Auswertegruppe fur die Bewertung der Genauigkeit der Hohenmodellgenerierung etabliert. Dabei sollte der DGPF-Test genutzt werden, um den derzeitigen Stand der Technik der photogrammetrischen 3D Erfassug mittels automatischer Bildzuordnung zu dokumentieren. Hierfur wurden DSM Raster und 3D Punktwolken aus Bildern der photgrammetrischen Kamerasysteme abgeleitetet und die Qualitat dieser Ergebnisse in Bezug auf Genauigkeit und Zuverlassigkeit bewertet. Dabei wurde ein Vergleich zu terrestrischen Referenzmessungen und flugzeuggestutzen LiDAR Daten durchgefuhrt. Neben der qualitativen Bewertung von Standardprodukten wurde auch die Nutzbarkeit der Hohendaten fur spezielle Anwendungen beispielsweise im Kontext der 3D Stadmodellierung und Forstwirtschaft untersucht.

Interpretation of Urban Surface Models Using 2D Building Information

In 3D building reconstruction the interpretation process can be simplified if digital surface models (DSM), which can either be derived from stereo matching of aerial images or be directly measured by scanning laser systems, are used in addition to or instead of image data. Images contain much information, but the resulting complexity causes enormous problems for an automatic interpretation of this data type. Since the information of a DSM is restricted to surface geometry its interpretation is simplified by the absence of unnecessary details. Nevertheless, due to insufficient spatial resolution and quality of the DSM, especially for these applications, optimal results can only be achieved by the use of additional data sources. Within the approach presented in this paper the segmentation of planar surfaces from the DSM is supported by existing ground plans. This 2D building information is also used to derive hypotheses on the possible roof shapes in order to obtain a 3D boundary representation based on the segmented planes.

Data fusion for the detection and reconstruction of buildings

Research in detection and reconstruction of man-made objects from aerial images has made significant progress in the past two or three years. Two important reasons for that are: (1) data fusion of different sources provides more information for the ill-posed image analysis processes and (2) more sophisticated algorithms are developed which apply grouping and reasoning processes using a model of the object class of interest.

Dense Multi-Stereo Matching for High Quality Digital Elevation Models

gorithms. Airborne imagery of good dynamic range and signal-to-noise ratio as it is generated by digital aerial cameras is highly beneicial for automatic image matching. This is especially true for surfaces with relatively little surface texture. Consequently, the quality and precision of image-based point transfer as the basis for 3D surface reconstruction has been improved considerably. Recent tests have already demonstrated the feasibility of image

Detection of buildings by fusion of range and image data

This paper addresses the issue of detecting buildings in aerial images by fusing range data and iconic image information. The range and image data are assumed to be captured by an integrated sensor system from a surveying aircraft. Fusion takes place on a symbolic level of image description. The segmented range data mainly are used for the detection of buildings whereas the image primitives extracted by a grouping algorithm are used for the verification and localization of building hypotheses. Terrain heights can be acquired by an airborne laser scanner. The height data are used to detect local maxima in height which give evidence for objects rising from the terrain surface like buildings do. Because the height data is relatively sparse it is impossible to detect the border lines of the buildings from these data. Therefore candidate regions are examined further by a grouping process. Buildings very often show parallelogram structures in aerial images. The grouping process detects these structures by combining image primitives applying relations like colinearity, parallelism, symmetry, and neighborhood.

A multi-sensor system for positioning in urban environments

Within the article a low-cost system for the provision of georeferenced terrestrial images in urban environments is presented. Based on an image with approximate exterior orientation from a low-cost GPS and a digital compass and a 3D CAD model of a visible model as provided from a 3D virtual city model, the exact location of the building in the image is detected automatically and used for a refined orientation of the image. The work is part of a project aiming on the development of a mobile device, which enables access to location-based services in a complex urban environment. The intuitive access to object-related information is realized by so-called telepointing. For this purpose, a spatial model of the users environment is mapped to an oriented image, allowing for the access to object-related information by pointing to the respective image sections. Since the provision of location-based services currently is one of the most promising markets for the use of spatial data in urban areas, these applications will also be discussed.

DGPF Project: Evaluation of Digital Photogrammetric Aerial-based Imaging Systems - Overview and Results from the Pilot Center

Within this paper, results of a test on the evaluation of the most recent photogrammetric digital airborne camera systems are presented. This project was initiated by the German Society of Photogrammetry, Remote Sensing and Geoinformation (DGPF), based on data from 12 different digital sensor systems flown in a well-controlled test site. The main topics of the evaluation phase are the analysis of geometric accuracy and sensor calibration, the radiometric performance including on-site radiometric calibration and multi-spectral land classifications, the performance of photogrammetric Digital Surface Model (DSM) generation, and the potential of manual stereoplotting from digital images. Within this paper, only results obtained at the Institute of Photogrammetry (IFP), Universitaet Stuttgart will be presented, comprehensively proving the high performance of digital camera systems and processing. The IFP served as the pilot center and additionally concentrated on the investigation of camera geometry and the image based generation of height data.

From mobile mapping to telegeoinformatics: Paradigm shift in geospatial data acquisition, processing, and management

Technological advances in positioning and imaging sensors, combined with the explosion in wireless mobile communication systems that occurred during the last decade of the twentieth century, practically redefined and substantially extended the concept of mobile mapping. The advent of the first mobile mapping systems (MMS) in the early 1990s initiated the process of establishing modern, virtually ground-control-free photogrammetry and digital mapping. By the end of the last decade, mobile mapping technology had made remarkable progress, evolving from rather simple land-based systems to more sophisticated, real-time multitasking and multisensor systems, operational in land and airborne environments. New specialized systems, based on modern imaging sensors, such as CCD (charge-coupled device) cameras, lidar (Light Detection and Ranging) and hyperspectral/multispectral scanners, are being developed, aimed at automatic data acquisition for geoinformatics, thematic mapping, land classification, terrain modeling, emergency response, homeland security, etc. This paper provides an overview of the mobile mapping concept, with a special emphasis on the MMS paradigm shift from the post-mission to near-real-time systems that occurred in the past few years. A short review of the direct georeferencing concept is given, and the major techniques (sensors) used for platform georegistration, as well as the primary radiolocation techniques based on wireless networks, are presented. An overview of the major imaging sensors and the importance of multisensor system calibration are also provided. Future perspectives of mobile mapping and its extension towards telegeoinformatics are also discussed. Some examples of mobile geospatial technology used in automatic object recognition, real-time highway centerline mapping, thematic mapping, and city modeling with lidar and multispectral imagery are included.

Extracting 3D urban models from oblique aerial images

Oblique airborne cameras are increasingly used for area covering image collection of building facades in urban environments. Until recently, these images were mainly used to improve the visual appearance of relatively simple 3D building models by providing suitable facade texture. Meanwhile, oblique airborne images are also used to generate dense 3D point clouds using state-of-the-art pixel-based multi-stereo image matching. Subsequently, these point clouds can then enhance the amount of geometric and semantic detail of 3D urban models especially for the depicted building facades. However, occlusions and large view-point changes are especially demanding during dense image matching can be very challenging for oblique imagery in complex urban environment. As described in the paper, our matching pipeline tackles these problems by a coarse-to-fine modification of the SGM method. Furthermore the raw 3D point clouds are efficiently analyzed and filtered in subsequent steps, thus 3D data capture from oblique airborne imagery while aiming at the extraction of 3D urban models becomes feasible.