Dieter Fritsch

Matching spatial data sets: a statistical approach

Although the acquisition and maintenance of spatial data is very costly and time consuming very often the same objects of the real world are captured in many different data models, at different acquisition times, with different quality characteristics or at different scales. This situation will become intensified when more and more digital spatial data are offered by using internet technologies. Integration methods are needed to take advantage of the characteristics of more than one data set. These advantages could be, for example, new applications for which the data models had not been originally designed, higher reusability, improvement of the quality, or cost minimization of data acquisition. In this paper a relational matching approach for integration of spatial data from different sources is introduced. The research work was performed on street centrelines which were captured in different data models. The approach is based on statistical investigations between the data of two data models, and can be ...

Progress in Cultural Heritage Preservation

In most cases archaeological finds and objects remain in the country of origin. Thus, for potential users away from that location, 3D models of archaeological finds and objects form an increasingly important resource since they can be analysed and visualised in efficient databases using web-based tools over the Internet. Since typical 3D recording technologies for archaeological objects, such as terrestrial laser scanning or fringe projection systems, are still expensive, cumbersome, inconvenient, and often require expert knowledge, camera-based systems offer a cost-effective, simple and flexible alternative that can be immediately implemented. This paper will demonstrate how the geometry and texture of archaeological finds and objects can be automatically constructed, modelled and visualized from digital imagery using freelyavailable open-source software or web services. The results of several objects derived from different tested software packages and/or services are compared with reference data in order to analyse the accuracy and reliability of such objects.

Accuracy of videometry with CCD sensors

Abstract For accurate computer vision based on standard video signals, the term Videometry is introduced. Some geometrical, optical and electrical properties of CCD-cameras in conjunction with analog/digital-converters and frame buffers are investigated: lens distortion, sensor distortion, anisotropic modulation transfer function, space-variant impulse response due to discrete sensor elements and insufficient optical low-pass filtering, horizontal line jitter and scaling factor due to mismatch of sensor-shift- and A/D-conversion-clock, noise etc. Based on these results, a very simple camera model with a special radial lens distortion equation is proposed. This allows for a fast, fully linear calibration algorithm (15 msec calibration time for 36 coplanar calibration points) with good accuracy ( 1 30 of a frame buffer pixel residual error). It requires independent pre-calibration of the principal point and the horizontal scale factor. The latter is performed by Fourier analysis of the aliasing patterns produced by interference of camera- and A/D-converter clock. Only small improvements (3% average error, 30% maximum error) were obtained by subsequent nonlinear optimization (self-calibration with bundle adjustment) using the results from the linear approach as initial guess.

4D Reconstruction of Tangible Cultural Heritage Objects from Web-Retrieved Images

The number of digital images that are available online today has reached unprecedented levels. Recent statistics showed that by the end of 2013 there were over 250 billion photographs stored in just one of the major social media sites, with a daily average upload of 300 million photos. These photos, apart from documenting personal lives, often relate to experiences in well-known places of cultural interest, throughout several periods of time. Thus from the viewpoint of Cultural Heritage professionals, they constitute valuable and freely available digital cultural content. Advances in the fields of Photogrammetry and Computer Vision have led to significant breakthroughs such as the Structure from Motion algorithm which creates 3D models of objects using their 2D photographs. The existence of powerful and affordable computational machinery enables the reconstruction not only of single structures such as artefacts, but also of entire cities. This paper presents an overview of our methodology for producing co...

Filtering and calibration of laser-scanner measurements

The paper introduces in airborne laser scanner architecture and its data postprocessing. One main problem is the definition of a contiguously measured digital terrain model (DTM) by filtering neighboring strips and their attachment to each other. These problems are solved by spline approximations and datum transforms. The spline approximation starts with a bicubic polynomial which can be reparameterized in terms of its function values and the first derivatives as new unknown parameters. Filtering is carried out in a two dimensional rectangle bordered by the nodes of the spline. The next step of the data postprocessing is the datum transform. Using a similarity transform the seven datum parameters have to be defined by a data snooping procedure with non-parametric hypothesis tests. The reason for using non- standard test statistics is the systematic effects produced by the sensor system itself are man- made and natural 3-D phenomena cannot be eliminated a priori perfectly. Therefore, the datum transform should give the hints which observations are blunders and which are not.

Photogrammetry and geographic information systems for quick assessment, documentation and analysis of earthquakes

Abstract After a catastrophe like an earthquake, one on the most important problems is to provide shelter and housing for the homeless. To this end, it is necessary to decide if a building is still habitable, or if it is has to be renovated or even torn down. A prerequisite for such decisions is the detailed knowledge about the status of the building. Earlier earthquakes revealed problems in the processes of documenting and analysing the building damage, as they demanded much effort in terms of time and manpower. The main difficulties appeared to be because of the analogue damage assessments which created a great variety of unstructured information that had to be put in a line to allow further analysis. Apart from that, documentation of damage effects was not detailed and could only be carried out on the spot of a disaster. The aim of this study is to make an improvement, using combination of Geographic Information Systems (GIS) as a management and data analysis tool and photogrammetry as a documentation method. Photogrammetric data acquisition is achieved using a CCD camera and the digital photogrammetric software package PICTRAN by Technet. The information system part is the GIS package ArcView by ESRI. The combination of rapid data acquisition and GIS offers a quick assessment of the situation and the possibility of its objective and holistic analysis. This is the prerequisite for a quick initiation of appropriate measures to help people.

Quality of Context

Invited Papers.- Interacting with Context.- The Quality of Geospatial Context.- Context Quality and Privacy - Friends or Rivals?.- Querying and Cleaning Uncertain Data.- Spatial Embedding and Spatial Context.- Contributed Papers.- A Context Quality Model to Support Transparent Reasoning with Uncertain Context.- On a Generic Uncertainty Model for Position Information.- A Probabilistic Filter Protocol for Continuous Queries.- Establishing Similarity across Multi-granular Topological-Relation Ontologies.- UDS: Sustaining Quality of Context Using Uninterruptible Data Supply System.- A Framework for Quality of Context Management.- An Abstract Processing Model for the Quality of Context Data.- Using Quality of Context to Resolve Conflicts in Context-Aware Systems.- Presentation and Evaluation of Inconsistencies in Multiply Represented 3D Building Models.- Bringing Quality of Context into Wearable Human Activity Recognition Systems.- Quality Dependent Reconstruction of Building Facades.

Multivariate hypothesis tests for detecting recent crustal movements

Abstract For detecting recent crustal movements repeated geodetic measurements are often observed in a net of control points. These data are evaluated in a multivariate statistical analysis, in order to separate the set of control points into two disjunctive sets, the set of fixed points and the set of variable points. The coordinates of the control points are introduced as unknown parameters for the analysis of the observations at different time epochs. However, the geodetic measurements often do not contain any information about the translation, the rotation or the scale of the coordinate system, so that restrictions have to be introduced to obtain estimable quantities. As shown, these restrictions must be formulated for all fixed points, in order to obtain a location of the control net which is optimal with respect to the detection of movements. But the fixed points have to be found first by means of univariate and multivariate hypothesis tests. This problem is solved by a successive estimation and test procedure, which can be automated, so that in a single analysis of the data the variable points are separated from the fixed points. As shown by an example, the univariate and multivariate test procedures enable the detection of horizontal movements in the order of magnitude of the lengths of the axes of the 95% confidence ellipses.

Nexus - the mobile GIS-environment

Individual mobility plays a crucial role in our everyday life. Since people spend a lot of time being mobile, making mobility more efficient is a demand of most of them. Due to the latest developments in the fields of computer technology and wireless communication, it has become possible for computer applications to meet the needs of mobile individuals. Since positioning techniques have also reached an acceptable accuracy, the location of users can be exploited by mobile applications, too. Thus, location-based services (LBS) evolved. They prepare information and services according to a users position. The data and operations they provide very much coincide with those available in GIS. For this reason, LBS can be understood as mobile GIS applications. At the University of Stuttgart, a research project called Nexus has been initiated to create an open and global environment for mobile GIS. The paper briefly introduces the idea of Nexus and describes the architecture and the data model of the platform. Then, approaches for spatial data integration are outlined.

4D reconstruction of the past

One of the main characteristics of the Internet era we are living in, is the free and online availability of a huge amount of data. This data is of varied reliability and accuracy and exists in various forms and formats. Often, it is cross-referenced and linked to other data, forming a nexus of text, images, animation and audio enabled by hypertext and, recently, by the Web3.0 standard. Search engines can search text for keywords using algorithms of varied intelligence and with limited success. Searching images is a much more complex and computationally intensive task but some initial steps have already been made in this direction, mainly in face recognition. This paper aims to describe our proposed pipeline for integrating data available on Internet repositories and social media, such as photographs, animation and text to produce 3D models of archaeological monuments as well as enriching multimedia of cultural / archaeological interest with metadata and harvesting the end products to EUROPEANA. Our main goal is to enable historians, architects, archaeologists, urban planners and affiliated professionals to reconstruct views of historical monuments from thousands of images floating around the web.