Maria Tsakiri

Evaluation of a pulsed terrestrial laser scanner based on ISO standards

The evaluation of the accuracy and precision of measuring equipment is critical in order to achieve results that meet the specifications of a given project. Standard calibration models and field procedures exist for all traditional surveying instruments, but are still lacking for recently developed technologies like terrestrial laser scanners (TLS). The main reason is limited knowledge of errors that affect these systems, owing to the proprietary design of the scanners and their software, and the integration of many potential sources of error. Owing to the difficulty of separating the different error sources of TLS, it is proposed in this paper that a test procedure can assess the overall achievable precision for a scanner instrument without individual errors being known. The proposed tests are based on the International Organization for Standardization specifications for geodetic instruments (www.iso.org). The tests can be performed in either a controlled or uncontrolled environment, which is advantageous for on-the-job calibration. A pulsed terrestrial laser scanner (Leica Scanstation 2) was used as a test subject and the evaluation results indicated that the specific instrument performed well within the manufacturers specifications.

The use of low-cost, single-frequency GNSS receivers in mapping surveys

The emergence of low-cost, navigation-type receivers capable to provide carrier-phase data (the so-called high-sensitivity carrier-phase positioning) has been steadily growing over the recent years. The aim of this study was to evaluate the positioning performance of a high-sensitivity receiver in a network real-time kinematic environment for mapping surveying applications. Specifically, using as rover receiver the u-blox NEO-7P module and the low-cost antenna Tallysman TW2410, sets of data were collected for the purpose of mapping surveying. The external accuracy of the obtained solutions is considered using different positioning techniques and the internal indicators of the system during real-time kinematic (RTK) positioning are assessed. The assessment indicates that in benign environments this type of receivers produce results that are comparable to RTK positioning using geodetic receivers and with a significantly lower cost.

Applications of Volunteered Geographic Information in Surveying Engineering: A First Approach

Volunteered Geographic Information (VGI) has been used in various scientific domains and applications. Surveying Engineering is a field that has not yet exploited concepts like data and service sharing and reuse. This paper aims to suggest a framework that will support data sharing in Surveying Engineering by creating an online spatio-temporal information repository for land surveying projects. A data model to meet the needs for Surveying Engineering applications and accuracy requirements is introduced to facilitate the sharing of VGI information among Surveying Engineers. A fully functional prototype system has been developed and used to apply the proposed methodology in a large scale study undertaken by the Greek Ministry of Culture which involves the mapping of the historic center of Athens as part of the Archaeological Cadastre project. Results coming from data analysis indicate a substantial (~60 %) error reduction and also significant productivity raise (~25 %), while at the same time, the collected data are structured and saved in an online database, accessible by community users—professional Surveying Engineers who can in turn contribute to further improve the available data and services according to the principles of VGI applications.

ON THE QUALITY OF DISTANCE MEASUREMENTS IN ATHLETIC THROWING EVENTS

Abstract Distance measurement in athletic throwing events is fundamentally a surveying problem which should follow the appropriate quality control procedures. This paper discusses the measurement procedure adopted by the IAAF (International Association of Athletics Federations) for throwing events, with particular emphasis on the javelin event. Published National Survey Standards are applied to form models of the errors associated with the IAAF procedure. The effect of these random error models on measured throwing distances is discussed statistically with probabilities of ‘miscarriages of justice’ (one athlete throwing less far than another but being awarded a longer distance by the officials) being presented. Finally some comments and recommendations regarding the IAAF measurement specifications are made.

The use of GPS for monitoring cable-stayed bridges in seismic areas

The regular monitoring of structures often requires measurement of relative displacements, which may, in turn, be used to assess the structure’s stress and drift conditions during, for example, seismic events. The instruments most commonly used to monitor structural systems during earthquakes are accelerometers. However, accelerometers do not directly measure structural displacements. Recent advances in Global Positioning System (GPS) technology can provide a supplementary sensor which can directly provide displacement information in real time.

Quality Control of Height Benchmarks in Attica, Greece, Combining GOCE/GRACE Satellite Data, Global Geopotential Models and Detailed Terrain Information

The incorporation of the newly available satellite data of GOCE and GRACE missions into global geopotential model solutions provides valuable information on the low to medium frequency band of the gravity field spectrum, an important connection to height datum control and unification. The use of this enriched contribution to existing national height systems quality control will reveal the well known inconsistencies in previous vertical network establishment methods, as well as strengthen the connection solution between adjacent national networks.

VGI in surveying engineering: Introducing collaborative cloud land surveying

Volunteered geographic information (VGI) has enabled many innovative applications in various scientific fields. This paper introduces a new framework called “collaborative cloud-based land surveying” (CCLS) that uses VGI principles for data sharing among surveyor engineers to boost the productivity and improve the quality of their applications. A cloud-based spatio-temporal data repository is presented, aiming to facilitate the sharing of VGI among surveyor engineers. A fully-functional distributed software application has been developed and used to apply CCLS in a large-scale land surveying project run by the Greek Ministry of Culture, which involves the mapping of the historic center of Athens. Results from the data analysis of hundreds of measurements indicate a substantial (30% to 60%) error reduction and also a significant productivity raise (∼22%). The collected measurements are shared in an online database, accessible by professional surveyors who can in turn contribute their own data to further enhance the CCLS system.