Thomas P. Kersten

Low-Cost and open-source solutions for automated image orientation --- a critical overview

The recent developments in automated image processing for 3D reconstruction purposes have led to the diffusion of low-cost and open-source solutions which can be nowadays used by everyone to produce 3D models. The level of automation is so high that many solutions are black-boxes with poor repeatability and low reliability. The article presents an investigation of automated image orientation packages in order to clarify potentialities and performances when dealing with large and complex datasets.

Image-Based low-cost systems for automatic 3d recording and modelling of archaeological finds and objects

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 freely-available 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.

Methods for Geometric Accuracy Investigations of Terrestrial Laser Scanning Systems

Currently the second, or for some manufacturers even the third, generation of terrestrial laser scanning systems is available on the market. Although the new generation of terrestrial 3D laser scanning offers several new (geodetic) features and better performance, it is still essential to test the accuracy behaviour of the new systems for optimised use in each application. As a continuation of previously published investigations the Department Geomatics of the HafenCity University Hamburg (HCU Hamburg) carried out comparative investigations into the accuracy behaviour of the new generation of terrestrial laser scanning systems (Trimble GX, Leica ScanStation 1 and 2, and Riegl LMS420i using time-of-flight method, Leica HDS6000, Z+F IMAGER 5006, and Faro LS880 HE using phase difference method). The results of the following tests are presented and discussed in this paper: test field for 3D accuracy evaluation of 3D laser scanning systems, accuracy tests of distance measurements in comparison to reference distances, accuracy tests of inclination compensation, and influence of the laser beam’s angle of incidence on 3D accuracy.

Potential of Automatic 3D Object Reconstruction from Multiple Images for Applications in Architecture, Cultural Heritage and Archaeology

Constant improvements in the performance of internet and computer technologies combined with rapid advancements in computer vision algorithms now make it possible to efficiently and flexibly reconstruct the 3D geometry of objects. Objects of different sizes can be modelled using image sequences from commercial digital cameras that are processed by web services and freely available software packages, forming low cost systems for numerous applications (restoration, historical care of monuments, visualization, analysis of the state of construction and the damage, etc.). In this contribution various cultural objects (historical buildings, statues/figures, archaeological finds, etc.) have been reconstructed in order to investigate the potential of this technology which enables the automatic generation of 3D point clouds or surface models (as 3D polygons) with photo-realistic texture from image data. These so-called low cost systems represent an efficient alternative to expensive terrestrial laser scanning syst...

Scale-dependent patterns of variability in species assemblages of the rocky intertidal at Helgoland (German Bight, North Sea)

A growing body of literature shows that benthic communities are hierarchically structured on spatial and temporal scales. In two study locations at Helgoland (North Sea), the northern and the western locations, we: (i) investigated the variation in abundance of specific algae and invertebrates at two spatial scales; and (2) evaluated the relationship between elevation and specific species at these scales. We were also interested in using this information about the spatial pattern of individual algae and invertebrates as well as the patterns of elevation to help develop a monitoring programme of the rocky intertidal. We examined the variation of individual algae and invertebrates by means of a hierarchical nested design. Data were taken from five replicates per plot, with plots located in transects (two transects per location). At the northern location, the highest variability in cover of most algae and invertebrates occurred at the scale separated by about so m (scale: transect). This was a direct result of differences between the high- and the low-shore. Most species at high-shore showed a relatively low frequency of occurrence in contrast to a highest frequency of occurence (∼100%) and maximal values of cover at low-shore. However, neither a linear nor a non-linear relationship between elevation and the specific species occurred. At the western location, the highest variability in most macroalgae and invertebrates investigated was among replicates (los of centimetres apart). No relationship between elevation and individual species occurred at this location. Macroalgae at both locations were more consistent over time than invertebrate species. Our results suggest that the relevant processes shaping the individual macroalgae and invertebrates at the Helgoland rocky intertidal vary between locations and the specific species. The potential causes of variation in macroalgal and invertebrate species at different spatial scales are discussed and suggestions for a future monitoring programme are given. Temporal inconsistency in the spatial patterns, and the fact that some individual algae and invertebrates comprising the benthic assemblages vary at different scales, speak in favour of a multiple-scale sampling approach for monitoring change in the intertidal communities at Helgoland.

Virtual architectural 3d model of the imperial cathedral (kaiserdom) of königslutter, germany through terrestrial laser scanning

The imperial cathedral (Kaiserdom) of Konigslutter, Germany, is one of the most important examples of Romanesque architecture north of the Alps. In April 2010 complex conservation and restoration works were finished to celebrate the 875th anniversary of the laying of the cathedrals foundation stone. The imposing structure of the cathedral was recorded internally and externally in 3D using terrestrial laser scanning in January and June 2010 as part of a student project at the HafenCity University Hamburg. The goal of the project was the 3D CAD construction of the cathedral using laser scanning point clouds to derive both a virtual and physical (replica) 3D model for the documentation and visualisation of the building. Furthermore, a virtual tour around and through the cathedral was generated from spherical panorama photographs, which were acquired from several camera stations surrounding and inside the building.

Automated generation of an historic 4d city model of hamburg and its visualisation with the GE engine

Current 3D city models are already available for many cities world-wide. However, the production of historical city models is still in its infancy. In this paper a procedure is presented that combines different data sources in order to derive individual 3D city models of different time periods using the example of the Free and Hanseatic City of Hamburg. A wooden model of the city from the year 1644 and an official map from 1859 have been used as a basis for the generation of the 4D city model. The physical model (~1:1000) was scanned by a fringe projection system for 3D modelling, while the digitized data from the map were combined with height information from different data sources. These two geo-referenced 3D city models were used to derive further epochs (1200, 1400, 1589 and 1700) using different historical birds-eye views (isometric views) of the city. For interactive navigation and visualization of the 4D city model a program was developed using the Google Earth Application Programming Interface.

3D scanning and modelling of the bismarck monument by terrestrial laser scanning for integration into a 3D city model of Hamburg

In the context of an integrated pilot study between the HafenCity University Hamburg, the Jade University of Applied Sciences in Oldenburg and the Agency for Geo-Information and Surveying Hamburg the Bismarck monument in Hamburg has been scanned with the Z+F IMAGER 5006 3D laser scanning system to generate a virtual 3D model of the monument from the laser scanning data using different programs. A substantial aspect for modelling was data reduction, since the generated 3D model has to be integrated into the city model of Hamburg with the smallest possible data volume. Therefore a combination of triangle meshing and CAD turned out to be an optimal solution. Furthermore, the extent to which the modelled data can be reduced by appropriate polygon decimation, in order to derive a geometrically correct and visually attractive result (virtual 3D model), has been investigated. The geometrical quality of the model was evaluated on the basis of reference values. As well as the integration of the virtual model into the city model of Hamburg the generated virtual model was also prepared for interactive visualisations. For the entire processing of the project time management of the individual work procedures has been calculated, in order to derive statements about the economy of the project. Thus conclusions/recommendations for further projects on object recording, modelling and visualization of such historical buildings and monuments using this procedure with this technology could be provided.

Geometric and radiometric evaluation of the DSW300 roll film scanner

Geometric and radiometric investigations performed with two LH Systems DSW300 scanners are presented. Their performance evaluation was carried out using good quality test patterns and accurate processing methods. The geometric tests include global and local geometric errors, misregistration between colour channels, geometric repeatability and determination of the geometric resolution. Efforts were made to separate the contribution of various error sources (especially mechanical positioning, vibrations and lens distortion) on the total error. The radiometric tests include investigations of noise, linearity, dynamic range, spectral variation of noise, and artifacts. After a brief description of the scanner, details on the above investigations, analysis and results are presented. Regarding the geometric accuracy, the RMS was 1.3‐1.9 mm and the mean maximum absolute error 4.5‐8 mm. The errors are bounded, i.e. on the average the 3 (99.7%) values are 3 RMS, and the maximum absolute error 3.7 RMS. The co-registration accuracy of colour channels was about 1 mm. The short and medium term repeatability was very high. With a linear Look Up Table (LUT) the radiometric noise level is 1 and 1‐1.5 grey values for 25 and 12.5 mm scan pixel size, respectively. The dynamic range is 2 D (D ::: density) with a very good linear response up to this value. One of the major remaining radiometric problems is dust. In both geometric and radiometric tests, no significant differences between R, G, B and B=W scans has been observed. These results show that the geometric and radiometric quality of the DSW300 has been very much improved as compared to the DSW200 and also other scanner models. This test was part of a long and fruitful cooperation between the manufacturer, a major user, and an academic institution and shows that honest and critical behaviour, as well as thorough understanding of the problems and a desire to search for solutions, can lead to significant improvements to the benefit of all.

Interactive 3D Visualisation of Architectural Models and Point Clouds Using Low-Cost-Systems

For interactive 3D visualisation of textured landscape and architecture models, which were created at the HafenCity University Hamburg as 3D CAD models or triangle meshes, the modern game engine Unity is used. Textured models and point clouds are presented in a viewer application so that the user can navigate as in a virtual world of a computer game. The point of view is interactively chosen by the user to access the model in a virtual walk through. Low-cost-system components such as 3D monitors are used for the stereoscopic display of the objects. By using a smart phone app, the device becomes a head mounted display to create an even more immersive exploration of the data. The inertial sensors of the phone are used for the tracking of the head. In order to control movements of the virtual point of view different controls are used. The controls are taken from classical game consoles or from “off the shelf” PC accessories. In the developed software the following navigation controllers can be used: Sony Dualshock3, Nintendo WiiMote & Nunchuk, Microsoft Kinect, Leap Motion, XSens MTi. At the moment the software processes meshed models in FBX format, while the point cloud data is imported using the ASCII coded PLY format (XYZRGB) and processed on the basis of DirectX 11.