Global ETD Search

1	Investigation and calibration of pulsed time-of-flight terrestrial laser scanners Reshetyuk, Yuriy January 2006 (has links) <p>This thesis has two aims. The first one is the investigation and analysis of the errors occurring in the measurements with pulsed time-of-flight (TOF) terrestrial laser scanners (TLS). A good understanding of the error sources and the relationships between them is necessary to secure the data accuracy. We subdivide these errors into four groups: instrumental, object-related, environmental and methodological. Based on our studies and the results obtained by other researchers, we have compiled an error model for TLS, which is used to estimate the single-point coordinate accuracy of a point in the point cloud, transformed to the specified coordinate system.</p><p>The second aim is to investigate systematic instrumental errors and performance of three pulsed TOF laser scanners – Callidus 1.1, Leica HDS 3000 and Leica HDS 2500 – and to develop calibration procedures that can be applied by the users to determine and correct the systematic errors in these instruments. The investigations have been performed at the indoor 3D calibration field established at KTH and outdoors. The systematic instrumental errors, or calibration parameters, have been estimated in a self-calibration according to the parametric least-squares adjustment in MATLAB®. The initial assumption was that the scanner instrumental errors are similar to those in a total station. The results have shown that the total station error model is applicable for TLS as a first approximation, but additional errors, specific to the scanner design, may appear. For example, we revealed a significant vertical scale error in the scanner Callidus 1.1, caused by the faults of the angular position sensor. The coordinate precision and accuracy of the scanners, estimated during the self-calibration, is at the level of several millimetres for Callidus 1.1 and Leica HDS 3000, and at the submillimetre level for Leica HDS 2500.</p><p>In other investigations, we revealed a range drift of up to 3 mm during the first few hours of scanning, presumably due to the changes in the temperature inside the scanners. The angular precision depends on the scanner design (“panoramic” or “camera-like”), and the angular accuracy depends on the significant calibration parameters in the scanner. Investigations of the influence of surface reflectance on the range measurements have shown that the indoor illumination and surface wetness have no tangible influence on the results. The type of the material does not affect, in general, the ranging precision for Callidus 1.1, but it affects the ranging precision and accuracy of the scanners Leica HDS 3000 and Leica HDS 2500. The reason may be different wavelength and, possibly, different design of the electronics in the laser rangefinders. Materials with high reflectance and those painted with bright “warning” colours may introduce significant offsets into the measured ranges (5 – 15 cm), when scanned from close ranges at normal incidence with the scanner Leica HDS 3000. “Mixed pixels” at the object edge may introduce a range error of several centimetres, on the average, depending on the type of the material. This phenomenon leads also to the distortions of the object size, which may be reduced by the removal of the “mixed pixels” based on their intensity. The laser beam intensity recorded by the scanner tends to decrease with an increased incidence angle, although not as assumed by the popular Lambertian reflectance model. Investigations of the scanner Leica HDS 2500 outdoors have revealed no significant influence of the “normal” atmospheric conditions on the range measurements at the ranges of up to 50 m.</p><p>Finally, we have developed and tested two simple procedures for the calibration of the vertical scale (and vertical index) error and zero error in laser scanners. We have also proposed an approach for the evaluation of the coordinate precision and accuracy in TLS based on the experiences from airborne laser scanning (ALS).</p> terrestrial laser scanning error sources calibration coordinate precision/accuracy
2	Investigation and calibration of pulsed time-of-flight terrestrial laser scanners Reshetyuk, Yuriy January 2006 (has links) This thesis has two aims. The first one is the investigation and analysis of the errors occurring in the measurements with pulsed time-of-flight (TOF) terrestrial laser scanners (TLS). A good understanding of the error sources and the relationships between them is necessary to secure the data accuracy. We subdivide these errors into four groups: instrumental, object-related, environmental and methodological. Based on our studies and the results obtained by other researchers, we have compiled an error model for TLS, which is used to estimate the single-point coordinate accuracy of a point in the point cloud, transformed to the specified coordinate system. The second aim is to investigate systematic instrumental errors and performance of three pulsed TOF laser scanners – Callidus 1.1, Leica HDS 3000 and Leica HDS 2500 – and to develop calibration procedures that can be applied by the users to determine and correct the systematic errors in these instruments. The investigations have been performed at the indoor 3D calibration field established at KTH and outdoors. The systematic instrumental errors, or calibration parameters, have been estimated in a self-calibration according to the parametric least-squares adjustment in MATLAB®. The initial assumption was that the scanner instrumental errors are similar to those in a total station. The results have shown that the total station error model is applicable for TLS as a first approximation, but additional errors, specific to the scanner design, may appear. For example, we revealed a significant vertical scale error in the scanner Callidus 1.1, caused by the faults of the angular position sensor. The coordinate precision and accuracy of the scanners, estimated during the self-calibration, is at the level of several millimetres for Callidus 1.1 and Leica HDS 3000, and at the submillimetre level for Leica HDS 2500. In other investigations, we revealed a range drift of up to 3 mm during the first few hours of scanning, presumably due to the changes in the temperature inside the scanners. The angular precision depends on the scanner design (“panoramic” or “camera-like”), and the angular accuracy depends on the significant calibration parameters in the scanner. Investigations of the influence of surface reflectance on the range measurements have shown that the indoor illumination and surface wetness have no tangible influence on the results. The type of the material does not affect, in general, the ranging precision for Callidus 1.1, but it affects the ranging precision and accuracy of the scanners Leica HDS 3000 and Leica HDS 2500. The reason may be different wavelength and, possibly, different design of the electronics in the laser rangefinders. Materials with high reflectance and those painted with bright “warning” colours may introduce significant offsets into the measured ranges (5 – 15 cm), when scanned from close ranges at normal incidence with the scanner Leica HDS 3000. “Mixed pixels” at the object edge may introduce a range error of several centimetres, on the average, depending on the type of the material. This phenomenon leads also to the distortions of the object size, which may be reduced by the removal of the “mixed pixels” based on their intensity. The laser beam intensity recorded by the scanner tends to decrease with an increased incidence angle, although not as assumed by the popular Lambertian reflectance model. Investigations of the scanner Leica HDS 2500 outdoors have revealed no significant influence of the “normal” atmospheric conditions on the range measurements at the ranges of up to 50 m. Finally, we have developed and tested two simple procedures for the calibration of the vertical scale (and vertical index) error and zero error in laser scanners. We have also proposed an approach for the evaluation of the coordinate precision and accuracy in TLS based on the experiences from airborne laser scanning (ALS). / QC 20101123 terrestrial laser scanning error sources calibration coordinate precision/accuracy
3	Self-calibration and direct georeferencing in terrestrial laser scanning Reshetyuk, Yuriy January 2009 (has links) An important step in data processing from terrestrial laser scanning (TLS) is georeferencing, i.e. transformation of the scanner data (point clouds) into a real world coordinate system, which is important for their integration with other geospatial data. An efficient approach for this is direct georeferencing, whereby the position and orientation of the scanner can be determined in the field, similarly to the working routine of total stations. Thus the efficiency of the survey can be increased, and the project time and costs reduced. An important factor that affects the results of TLS surveys, especially those with direct georeferencing, is scanner calibration. In the recent years, the method of self-calibration used in photogrammetry has become popular for the recovery of systematic errors in laser scanners. This thesis has two main aims. The first one is to develop an approach for self-calibration of terrestrial laser scanners, which can be made available to users, and apply it to the calibration of a number of pulsed laser scanners in order to get a better insight into the systematic instrumental errors present in these instruments. The second aim is to investigate the possibilities for direct georeferencing in TLS in static applications, with the focus on the use of GPS for this purpose, and to develop a survey system based on the combination of TLS and GPS. An additional aim of the thesis is to make a systematic description of the error sources in TLS surveys, where direct georeferencing is employed. A good understanding of these error sources is necessary to secure the data accuracy. We subdivide these errors into four groups: instrumental, object-related, environmental and georeferencing. We have developed a unified approach for self-calibration of terrestrial laser scanners, where one can introduce stochastic information about all the estimated parameters, which helps in reducing their correlations. In part, it is possible to use direct georeferencing to determine the exterior orientation parameters of the scanner. We applied this approach to the self-calibration of the pulsed scanners Callidus CP 3200, Leica HDS 3000 and Leica Scan Station. The initial assumption was that the scanner systematic instrumental errors, or calibration parameters, were similar to those in a total station. However, other errors not explained by the “a priori” total station error model can be present in the scanners. We revealed two such errors – the scale errors in the vertical angles and horizontal directions in the scanners Callidus CP 3200 and Leica HDS 3000, respectively. Most systematic errors were estimated with relatively high precision and low correlations with other system parameters. We have developed a prototype combined survey system, which allows the user to use GPS for direct georeferencing of the scanner parallel to the scanning. In the current implementation, the system consists of the scanning system Leica Scan Station 2, 2 GPS receivers and antennas from Leica and a number of necessary accessories. The scanner position can be determined from RTK (or possibly Network-RTK) measurements with the accuracy of better than 1 cm, both in plane and height. The position of the backsight target can be determined from post-processing of static GPS measurements with similar accuracy. In order to estimate the accuracy of the combined system and its efficiency in a typical TLS survey, we carried out several test measurements. The results have shown that it is possible to achieve the coordinate accuracy of better than 1 cm at the object distance of up to 50 m. This is comparable to the accuracy of conventional direct georeferencing, i.e. when the scanner is centred over a known point. The time expenses for the test survey of a building located at KTH campus, starting from the planning and finishing with the georeferenced point cloud, were about 1.5 workdays. The time expenses could be reduced further if the system was installed on a moving platform during the fieldwork. Hence, the combined system can be successfully used for the surveys of built environments, e.g. engineering constructions and historical monuments, which can be carried out fast and with high accuracy. / QC 20100806 / 3D laser scanning of engineering constructions and historical monuments terrestrial laser scanning self-calibration direct georeferencing error sources Surveying Lantmäteri
4	Analys av felkällor vid mängdavtagning av ventilationssystem ur BIM-modeller / Analysis of error sources in quantity take off in ventilation systems from BIM models Kakar, Adib, Turan, Ensari January 2014 (has links) De senaste åren har det skett stora framsteg i byggbranschen från sedvanlig byggprojektering till avancerad BIM-projektering. Resultatet av denna studie visar att trots den hastiga utvecklingen så utförs det fortfarande mängdavtagningar ur 2D-ritningar. Detta på grund av problem som uppstår vid mängdavtagningar ur objektbaserade 3D-modeller. Mängdlistorna ur objektbaserade 3D-modeller stämmer inte alltid överens med mängdlistorna ur 2D-ritningar. Detta leder i sin tur till nödvändiga och tidskrävande manuella mängdavtagningskontroller ur pappersritningar. Detta för att säkerhetsställa den riktiga mängden. Ju större projekten blir, desto mer tid tar det att utföra de manuella mängdavtagningskontrollerna. Syftet har varit att lokalisera och analysera de olika felkällorna som uppkommer vid mängdavtagningar. Mängdavtagningsfunktionen i programmet RevitMEP (2014) och MagiCAD (2013.11) undersöktes. Resultatet jämfördes med manuella mängdavtagningar ur 2D-ritningar. Examensarbetet resulterade i en arbetsmodell som visar hur man på ett korrekt sätt utför mängdavtagningar ur 3D-modeller. Vinsten av detta blir att färre återkommande fel uppstår. Det är viktigt att ha ett välstrukturerat och tydligt arbetssätt vid användning av de olika BIM-verktygen. Vid användning av modellen blir det färre fel och minskad missförstånd uppstår vid projektering. Kontinuerliga mängdavtagningar bör genomföras för att så tidigt som möjligt möjliggöra upptäckten av fel. Att upptäcka felen i ett tidigt skede förhindrar att felet eskalerar. I studien påträffades även ett kritiskt programmeringsfel i programmet MagiCAD för Revit MEP vilket ger användaren felaktiga resultat. Problemet har påpekats till programutvecklaren CADCOM och korrigering av programmet kommer att ske. / The past years there have been vast progresses within the construction industry from traditional construction projection method to a more advanced BIM-projecting method. The results of this dissertation shows that in spite of these vast progresses it is still commonly conducted manual quantity calculations with 2D-drawings. The main reason to this is that when you compare the quantity results from object based 3D models to manual quantity calculation results with 2D-drawing, the results do not add up being equal to each other. Hence time consuming manual quantity calculations with paper drawings has to be conducted to verify the real material quantity. The larger the project, the more time is consumed to conduct manual calculation verification. The aim has been to identify and analyze the different sources of error arising from manual calculation verification. In assistance we used the quantity calculation functions in the software RevitMEP (2014) and MagiCAD (2013.11). To substantiate the results manual calculations were conducted. The results were compared to the manual calculations from 2D drawings, the profit of the method is that we get less reoccurring errors. The gain of this is resulting in fewer recurring of errors. It is important to have a well-structured and clear approach with the use of the various BIM tools. When using the model, there are fewer errors and reduced misunderstandings arise during project planning. Continuous calculation verifications should be implemented as early as possible to allow the discovery of errors. Detecting errors in the early stage will prevent the error from escalating. The study also found a critical programming error in the program MagiCAD for Revit which gives the user false results. The problem has been pointed out to the application developer CADCOM and correction of the program will occur. quantity Revit MEP MagiCAD BIM error sources mängdavtagning Revit MEP MagiCAD BIM felkälla Civil Engineering Samhällsbyggnadsteknik
5	Satellite Attitude Determination Using Laser Communication Systems Sabala, Ryan J. 25 September 2008 (has links) No description available. Electrical Engineering Satellite Attitude Determination Laser Communication System Satellite Laser Communication Sensitivity Analysis Static Estimation Error Sources
6	Challenges of regional hydrological modelling in the Elbe River basin : investigations about model fidelity on sub-catchment level Conradt, Tobias January 2013 (has links) Within a research project about future sustainable water management options in the Elbe River basin, quasi-natural discharge scenarios had to be provided. The semi-distributed eco-hydrological model SWIM was utilised for this task. According to scenario simulations driven by the stochastical climate model STAR, the region would get distinctly drier. However, this thesis focuses on the challenge of meeting the requirement of high model fidelity even for smaller sub-basins. Usually, the quality of the simulations is lower at inner points than at the outlet. Four research paper chapters and the discussion chapter deal with the reasons for local model deviations and the problem of optimal spatial calibration. Besides other assessments, the Markov Chain Monte Carlo method is applied to show whether evapotranspiration or precipitation should be corrected to minimise runoff deviations, principal component analysis is used in an unusual way to evaluate local precipitation alterations by land cover changes, and remotely sensed surface temperatures allow for an independent view on the evapotranspiration landscape. The overall insight is that spatially explicit hydrological modelling of such a large river basin requires a lot of local knowledge. It probably needs more time to obtain such knowledge as is usually provided for hydrological modelling studies. / Innerhalb eines Forschungsprojekts zu zukünftigen nachhaltigen Optionen der Wasserwirtschaft im Elbe-Einzugsgebiet mußten quasi-natürliche Abflußszenarien bereitgestellt werden. Zu diesem Zweck wurde das räumlich diskretisierte ökohydrologische Modell SWIM eingesetzt. Nach den von dem stochastischen Klimamodell STAR angetriebenen Szenariosimulationen würde die Region deutlich trockener werden. Allerdings ist das Hauptthema dieser Dissertation die Herausforderung, die Ansprüche an hohe Modelltreue auch für kleinere Teileinzugsgebiete zu erfüllen. Normalerweise ist die Qualität der Simulationen für innere Punkte geringer als am Gebietsauslaß. Vier Fachartikel-Kapitel und das Diskussionskapitel beschäftigen sich mit den Gründen für lokale Modellabweichungen und dem Problem optimaler räumlicher Kalibrierung. Unter anderem wird die Markovketten-Monte-Carlo-Methode angewendet, um zu zeigen, ob Verdunstung oder Niederschlag korrigiert werden sollte, um Abweichungen des Abflusses zu minimieren, die Hauptkomponentenanalyse wird auf eine unübliche Weise benutzt, um lokale Niederschlagsänderungen aufgrund von Landnutzungsänderungen zu untersuchen, und fernerkundete Oberflächentemperaturen erlauben eine unabhängige Sicht auf die Verdunstungslandschaft. Die grundlegende Erkenntnis ist, daß die räumlich explizite hydrologische Modellierung eines so großen Flußeinzugsgebiets eine Menge Vor-Ort-Wissen erfordert. Wahrscheinlich wird mehr Zeit benötigt, solches Wissen zu erwerben, als üblicherweise für hydrologische Modellstudien zur Verfügung steht. ökohydrologische Modellierung räumliche Kalibrierung Fehlerquellen der Modellierung Landschaftseffekte Fernerkundung eco-hydrological modelling spatial calibration modelling error sources landscape effects remote sensing Earth sciences
7	Impacts of Station Dependent Error Sources on the Implementation of the National Height Modernization Program Crawford, Justin Luvene January 2013 (has links) No description available. Civil Engineering Geographic Information Science National Height Modernization program GPS Station Dependent Error Sources Vertical Datum Orthometric Heights Multipath Near-Field Multipath Far-Field Multipath Antenna Phase Center Variation
8	The role of tree height and wood density for the water use, productivity and hydraulic architecture of tropical trees Link, Roman Mathias 19 February 2020 (has links) No description available. 570 Sap flux density Sap velocity Transpiration Water use Error sources Gravimetric flow determination Sap flow Radial profile Heat field deformation Hierarchical Bayes Dry forest Functional traits Growth rate Hydraulic efficiency Net primary production Structural equation modelling Wood anatomy Hydraulic conductivity Plant ecology Plant ecophysiology Plant drought responses Biologie (PPN619462639)
9	Die fehleranalytische Relevanz der prädominanten Spracherwerbshypothesen / Untersuchung des Fehlererklärungspotentials der Kontrastiv-, der Identitäts- und der Interlanguagehypothese auf Grundlage einer Analyse linguistischer Fehlleistungen deutscher Muttersprachler beim Erwerb des Englischen / The error analytical applicability of the predominant language acquisition hypotheses / Comparative examination of the error explanation potential of the contrastive, identity and interlanguage hypotheses based on the analysis of linguistic errors made by native speakers of German when acquiring the English language Achten, Michael 24 July 2006 (has links) No description available. 420 Englisch Philosophy Auslassungsfehler Deutsche Englischlernende Erstspracherwerb falsche Freunde Fehler Fehleranalyse Fehlerentstehungsfaktor Fremdsprachendidaktik Hinzufügungsfehler Identitäts-Hypothese Interlanguage-Hypothese Interlinguale Interferenz Intralinguale Interferenz Kommunikationsstrategien Kontrastivhypothese Kontrastmangel Lernstrategien Lexik Linguistik Morphologie Orthographie Spracherwerb Spracherwerbsforschung Spracherwerbshypothesen Substitution Syntax Zielsprache Zweitspracherwerb addition errors contrastive hypothesis didactics of foreign language learning error error analysis error sources false friends first language acquisition German learners of English interlanguage hypothesis interlingual interference intralingual interference L1=L2 hypothesis lack of contrast language acquisition language acquisition hypotheses language acquisition research lexis linguistics morphology omission errors orthography second language acquisition strategies of second language learning substitution syntax target language 17.31 Spracherwerb

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