Volker Schwieger

Ensuring globally the TanDEM-X height accuracy: Analysis of the reference data sets ICESat, SRTM and KGPS-tracks

The TanDEM-X mission will derive a global digital elevation model (DEM) with satellite SAR interferometry. Height references play an important role to ensure the required height accuracy of 10m absolute and 2m relative for 90% of the data. In this paper the main height reference data sets ICESat (for DEM calibration), SRTM (for phase unwrapping) and kinematic GPS-Tracks (KGPS — for DEM verification) are analyzed regarding to their accuracy. For the ICESat data a reliable quality measure is developed. For SRTM an improved version adjusted to reliable ICESat data is presented and a concept for collecting and evaluating decimeter-precise kinematic GPS tracks is proposed.

Sensitivity analysis as a general tool for model optimisation – examples for trajectory estimation

This paper outlines the general characteristics of variance-based sensitivity analysis and their advantages with respect to other concepts of sensitivity analysis. The main benefit are qualitative and quantitative correct results independent of the model characteristics. The author focuses on kinematic positioning as required for car navigation, driver assistance systems or machine guidance. The paper compares two different Kalman filter approaches using variance analysis and variance-based sensitivity analysis. The approaches differ with respect to their measurement quantities (input), their state quantities (output), as well as their dynamic vehicle model. The sensitivity analysis shows that each model has its different advantages and input-output relations. Furthermore it is shown that the variance-based sensitivity analysis is well suited to detect the share of the influence of the input quantities on the output quantities, here the estimated positions. Even more important, changes in deterministic and stochastic models lead to obvious effects in the respective variances and sensitivity measures. This emphasises the possibility to optimise the filter models by use of the variance-based sensitivity analysis.

Mobile positioning for traffic state acquisition

The topics presented in this article are related to the project ‘Data Optimisation for integrated Telematics’ (Do-iT) granted by the German Ministry of Economics and Technology. Within this project the current traffic state will be derived by use of network-based data from numerous mobile phones of anonymous drivers. With respect to traditional methods such as local loop data and GPS-based floating car data (FCD), this method (floating phone data, FPD) will take advantage of area-wide availability without additional infrastructure and costs. The timing advance (TA) value and signal strength measurements to the serving antenna are available in the GSM network, as well as signal strength measurements to up to six neighbouring antennas. The TA value is used to determine the distance from the serving antenna to the mobile phone. From this a search area is generated. The position of the mobile phone is determined by use of the signal strengths, which are matched to a signal strength map. These positions are referenced to the digital road network. Positioning is used to enable a reliable traffic prediction as a base for modern traffic control and management. Within this article a brief overview of the project is given, with the main focus being on the positioning methods. Different approaches based on least squares adjustment and Kalman filtering are presented and first results from data measured in the vicinity of the city of Stuttgart are presented.

Biomimetic Lightweight Timber Plate Shells: Computational Integration of Robotic Fabrication, Architectural Geometry and Structural Design

The research presented in this paper pursues the development and construction of a robotically fabricated, lightweight timber plate system through a biologically informed, integrative computational design method. In the first part of the paper, the authors give an overview of their approach starting with the description of the biological role model and its technical abstraction, moving on to discuss the computational modelling approach that integrates relevant aspects of biomimetics, robotic fabrication and structural design. As part of the validation of the research, a full-scale, fully enclosed, insulated and waterproof building prototype has been developed and realized: The first building featuring a robotically fabricated primary structure made of beech plywood. Subsequently, the methods and results of a geodetic evaluation of the fabrication process are presented. Finally, as the close collaboration between architects, structural and geodetic engineers, and timber fabricators is integral to the process, the architectural and structural potentials of such integrative design processes are discussed.

Modeling of quality for engineering geodesy processes in civil engineering

Abstract Automation of processes, in combination with quality assurance, is an important development in civil engineering. One of the critical components of quality assurance relates to geometry. In order to determine and control geometric elements, measurement and evaluation processes of engineering geodesy must be integrated with construction processes. The quality of products and processes is a complex, multi-faceted field and this complexity is considered here by a new model that describes quality on the basis of characteristics and parameters. The model that has been developed for engineering geodesy processes in civil engineering has been applied to describe the quality of the geometry of a building.

Static GNSS precise point positioning using free online services for Africa

The GNSS precise point positioning (PPP) technique has been extensively covered in recent research. In this study, six International global navigation satellite system (GNSS) Service (IGS) stations defined by 4-digits code in Africa were selected to be processed. The stations cover different climates in Africa. HARB, SUTH and WIND stations cover the mid-latitude area and NKLG, NURK and MAL2 are located in the equatorial region. Two data sessions were selected in processing to cover the winter and summer seasons: the first session of 3 days [01–03 January 2013 (DOY: 001–003/2013)] and the second session of 3 days [01–03 July 2013 (DOY: 182–184/2013)]. This paper aims to evaluate the accuracy of static PPP coordinate solution in Africa for different convergence times using free online services: Canadian Spatial Reference System (CSRS)-PPP, Automatic Precise Point Service (APPS)-PPP and GPS Analysis and Positioning Software (GAPS)-PPP. The stations’ observation times were divided into different observation times (1, 2, 4, 8, 12, and 24 h).The PPP coordinate solution was compared to the reference solution of those stations. The investigation is continued by estimating the PPP total tropospheric zenith delay (TZD) parameters, which were obtained by the different online services. These parameters were compared to the published parameters from IGS. The comparison between the different online services shows that the CSRS-PPP provides the best solution after 4 and 8 h. The APPS-PPP and CSRS-PPP provides the same solution in millimeters level after 12 h. In the equatorial region, the PPP coordinate solution is significantly improved between 12 and 24 h. Moreover, GAPS-PPP is not recommended to be used in the equatorial stations, where it shows a high error compared to CSRS-PPP and APPS-PPP even after 24 h. The mid-latitude stations show a better PPP coordinate solution in the winter than in the summer, but the equatorial stations present a low accuracy for the two sessions. Regarding the PPP tropospheric delay estimation, an additional station (HNUS) is used in the mid-latitude area, which has a low ellipsoidal height. APPS-PPP shows the best solution in the TZD estimation. The GAPS-PPP online service shows a systemic error in estimation and a high RMS relative to the TZD values known from IGS. The ellipsoidal height for antenna indicates a negative correlation to the estimated tropospheric values, but there is no effect for the variation of the ellipsoidal height in the estimated RMS. The estimated tropospheric parameters are correlated with the PPP coordinate estimation, where the GAPS-PPP service provides the worst PPP coordinate solution and at the same time, it shows the worst accuracy for tropospheric parameters estimation. Moreover, the estimated tropospheric parameters for the mid-latitude stations in the summer season show a higher RMS than in the winter season, which matches the same sequence of the PPP coordinates. The NKLG and NURK stations present a low accuracy for the tropospheric estimation, which is matching to the low accuracy of the PPP coordinates obtained from the different online services.

Mobile phone positioning for traffic state acquisition

Abstract Up to now different methods for the determination of positions and velocities of road users such as e.g. floating car data (FCD) or local loop data are used for traffic state acquisition and forecast. This paper deals with the determination of trajectories of road users applying information which are available within the GSM network. The signal strength and timing advance values are the measurements introduced into different least-square algorithms to determine positions. One alternative estimates the positions by distance measurements and further static information of the GSM network, the second alternative matches measured signal strengths on a given signal strength map. Both solutions are smoothed afterwards in parallel by a moving average filter and a Kalman filter algorithm. The resulting trajectories are matched on a digital road map using routing algorithms and map aiding procedures. These trajectories are called floating phone data (FPD). First intermediate results show an accuracy of approximately 200 to 300 m for the signal strength matching approach. For the time being correctness of the identified digital road elements is given for rural and suburban regions only. Further investigations have to be realised regarding the verification of these intermediate results as well as the extension of road identification to urban areas.

A synthetic covariance matrix for monitoring by terrestrial laser scanning

Abstract Modelling correlations within laser scanning point clouds can be achieved by using synthetic covariance matrices. These are based on the elementary error model which contains different groups of correlations: non-correlating, functional correlating and stochastic correlating. By applying the elementary error model on terrestrial laser scanning several groups of error sources should be considered: instrumental, atmospheric and object based. This contribution presents calculations for the Leica HDS 7000. The determined variances and the spatial correlations of the points are estimated and discussed. Hereby, the mean standard deviation of the point cloud is up to 0.6 mm and the mean correlation is about 0.6 with respect to 5 m scanning range. The change of these numerical values compared to previous publications as Kauker and Schwieger [17] is mainly caused by the complete consideration of the object related error sources.

Modeling and Propagation of Quality Parameters in Engineering Geodesy Processes in Civil Engineering

Quality assurance in civil engineering is a complex and multifaceted field. Especially for successful automation it plays an important role. One aspect of the quality assurance relates to the geometry of a building. In order to determine and control geometric elements, measurement and evaluation processes of engineering geodesy have to be integrated into the construction processes. So the task of engineering geodesy is to create the basis for bringing the planned building geometry in quality-assured reality.

A contribution to construction machine automation

Abstract The requirements concerning surveying tasks on modern construction sites have considerably changed. The time slots for assigning and assuring geometric properties get shorter. Thus the surveying tasks change from static to kinematic methods. Nowadays surveying instruments, e.g. robot-tachymeters, can work in real time due to more powerful CPUs and better synchronisation of internal sensors. Therefore it is possible to integrate robot-tachymeters into the construction process using control loops to fulfil the real time positioning task. Accuracy limiting factors like inclined reflector booms on the construction machine, temperature influence as well as synchronisation and dead time problems are pointed out, too. In this paper a modular toolbox for solution of geometric guidance and control tasks by robot-tachymeters is developed based on a so-called functional analysis and basic aspects of system design. The tachymeters are integrated into the processes to accomplish geometric control tasks of high precision (standard deviation < 1 cm for the position). The exemplary realisation of the modular system is the automatic guidance of a truck model (1:14) on a known trajectory.