06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access Terrestrial laser scanning - a supplementary approach for 3D documentation and animation(2005) Böhm, JanWhile aerial methods undesputedly form the backbone of modern photogrammetry, we have seen an increased use of terrestrial methods in the past years to supplement aerial data especially in the field of 3D city modelling and the animation thereof. This article describes an approach to use terrestrial laser scanning in order to increase detail and realism of datasets derived from arial methods. When devising a new strategy for the integration of data from multiple sources two aspects come to focus. For one methods for the registration of the datasets are needed. Secondly a suitable data model has to be introduced to hold multiple aspects of the data. Consequently we present our methods for the automatted georeferencing of terrestrial laser data and we introduce the concept of LASERMAPs, which are extracted from terrestrial laser data and mapped onto the 3D building model.Item Open Access Automation in laser scanning for cultural heritage applications(2005) Böhm, Jan; Haala, Norbert; Alshawabkeh, YahyaWithin the paper we present the current activities of the Institute for Photogrammetry in cultural heritage documentation in Jordan. In particular two sites, Petra and Jerash, were recorded using terrestrial laser scanning (TLS). We present the results and the current status of the recording. Experiences drawn from these projects have led us to investigate more automated approaches to TLS data processing. We detail two approaches within this work. The automation of georeferencing for TLS data is presented along with our approach for automated feature extraction.Item Open Access Development of a wind turbine LiDAR simulator(2009) Schlipf, David; Trujillo, Juan José; Basterra, Valeria; Kühn, MartinRemote sensing techniques like LiDAR offer many novel applications to the wind energy community, e.g. fast and accurate measurements of inflow and wake wind fields from the turbine nacelle. The prospects of such a new technique are evaluated with a software tool simulating a nacelle-based LiDAR system. The paper presents the implementation and application of a simulator that has been conceived to support the design of wind field scanning procedures. The tool helps to optimize the hardware setup, scanning trajectories and frequency. Furthermore it can be coupled with an aeroelastic code with the aim of developing a predictive control based on remote sensing.Item Open Access Efficient integration of aerial and terrestrial laser data for virtual city modeling uUsing LASERMAPs(2005) Böhm, Jan; Haala, NorbertOne of the first steps during evaluation of terrestrial LIDAR measurement is the co-registration of the data sets, which are collected from different stations and their transformation to a suitable reference coordinate system. As it is demonstrated within the paper, this can be achieved automatically, if low-cost components are used for direct georeferencing parallel to LIDAR measurement. By these means the position and orientation of the laser scanner can be determined. Further refinement is feasible, if the terrestrial scans are aligned to a DEM from airborne LIDAR or existing 3D building models. Frequently, terrestrial lasers scanning (TLS) is used to collect building facades at a large amount of geometric detail. For this type of application, the integration of existing 3D building models from airborne data collection as complimentary data source is especially suitable for the modeling step. Due to viewpoint restrictions of airborne data collection, the amount of detail, which is available for the building facades, is very limited. Thus, after alignment, the terrestrial scans are ideally suited to refine these models. However, as it is demonstrated in the second part of the paper, the large effort required for explicit modeling can be avoided if so-called LASERMAPs are extracted from TLS and mapped against the coarse 3D building model.Item Open Access Lidar technology for the German offshore test site "alpha ventus" - joint project in measurement development(2008) Rettenmeier, Andreas; Schlipf, David; Wächter, Matthias; Käsler, Yvonne; Mellinghoff, Harald; Siegmeier, Björn; Reeder, Lennard; Kühn, MartinThis paper describes the content of the joint research project "Development of LiDAR measurement techniques for the German offshore test site" and its first results. The objective is to develop reliable and standardised remote sensing techniques for various new applications in the wind energy community and to support other RAVE1 projects at the German offshore test site "alpha ventus". The first measurement campaign dealt with the comparison of wind parameters measured by common anemometry in a height of up to 103 m and LiDAR data measured up to 220 m height. The first results show very good agreement when the two techniques are compared as to wind speed, wind direction and power curve determination at a 5 MW wind turbine. The status of the development of a wind field scanner for nacelle-based LiDAR measurements is described and an outlook to the forthcoming work is given.Item Open Access Model-based segmentation and recognition from range data(2005) Böhm, JanThis paper aims at developing a model-based system for the object recognition of three-dimensional objects with curved surfaces using range images. The model data is represented using a CAD-model, providing a mathematical precise and reliable description of arbitrary shapes. The proposed method is based on model-based range image segmentation, using curvature as invariant features. By integrating model information into the segmentation stage, the segmentation process is guided to provide a partitioning corresponding to that of the CAD-model. The work provides a way to detect objects in arbitrary positions and derive the transformation onto a CAD-model. Thereby it contributes to the development of automated systems in the areas of inspection, manufacturing and robotics.Item Open Access Prospects of a collective pitch control by means of predictive disturbance compensation assisted by wind speed measurements(2008) Schlipf, David; Kühn, MartinA simple but robust and effective method to improve collective pitch control of variable-speed wind turbines given information on future inflow is proposed. The present paper focuses on the design and prospects of a control concept using predictive disturbance compensation. This feed-forward control structure is based on calculation of a future effective wind speed, on static disturbance compensation from steady turbine data and on estimation of the dynamic behavior. The control strategy is evaluated with regards to stability, robustness and performance in frequency and time domain. The required wind field information is currently not available for common control, but can in general be obtained from measurements with remote sensing technologies and wind modeling. Significant reductions of rotor speed variations, mechanical loads and pitch activity at fatigue and extreme operating conditions are demonstrated.Item Open Access From point samples to surfaces - on meshing and alternatives(2005) Böhm, Jan; Pateraki, MariaTerrestrial laser scanners deliver a dense point-wise sampling of an object’s surface. For many applications a surface-like reconstruction is required. The most typical example is the visualization of the scanned data. Traditional approaches use meshing algorithms to reconstruct and triangulate the surface represented by the points. Especially in cultural heritage, where complex objects with delicate structures are recorded in highly detailed scans, this process is not without problems. Often long and tedious manual clean-up procedures are required to achieve satisfactory results. After summarizing our experience with current meshing technology we therefore explore alternative approaches for surface reconstruction. An alternative approach presented within this paper is point splatting. We have developed an algorithm to compute a suitable surfel representation directly from the raw laser scanner data. This results in a speedy and fully automated procedure for surface reconstruction. The properties of the different approaches for surface reconstruction are discussed considering a practical example from the field of cultural heritage. The Panagia Kera in Kritsa near Agios Nikolaos on the island of Crete was chosen as a suitable example.Item Open Access An innovative algorithm to accurately solve the Euler equations for rotary wing flow(1992) Wagner, Siegfried; Krämer, EwaldDue to the ability of Euler methods to treat rotational, nonisentropic flows and also to correctly transport on the rotation embedded in the flow field it is possible to correctly represent the inflow conditions on the blade in the stationary hovering flight of a helicopter, which are significantly influenced by the tip vortices (blade-vortex interaction) of all blades. It is shown that also the very complex starting procedure of a helicopter rotor can be very well described by a simple Euler method that is to say without a wake model. The algorithm based on the procedure is part of category upwind schemes, in which the difference formation orientates to the actual, local flow state that is to say to the typical distrubance expansion direction. Hence, the artificial dissipation required for the numerical stability is included in a natural way adapted to the real flow state over the break-up error of the difference equation and has not to be included from outside. This makes the procedure robust. An implicit solution algorithm is used, where the invertation of the coefficient matrix is carried out by means of a Point-Gauss-Seidel relaxation.Item Open Access Georeferencing of terrestrial laserscanner data for applications in architectural modeling(2005) Schuhmacher, Sara; Böhm, JanCommonly several measurements originating from different sensor systems and stations are combined in order to completely model an architectural site. An important step preceding data fusion is the geometric alignment of the measurements with a geodetic coordi-nate system, or in other words georeferencing the measurements. This paper investigates methods for the georeferencing of terrestrial laserscanning data. Both sensor- and data-driven methods are considered. We propose the integration of a GPS receiver and a digital compass for automated georeferencing. We detail on how virtual city models and aerial LIDAR data can be utilized for georeferenc-ing by point cloud matching. The proposed methods are evaluated in practical experiments and compared to conventional methods. The results obtained are presented and illustrated.