A systematic approach to airborne sensor orientation and calibration: method and models

Avui dia, s'estima que el mercat de la geom atica mou pels volts de 30 bilions d'euros. Al darrera del creixement d'aquest mercat hi trobem noves tecnologies,projectes i aplicacions, com per exemple, \Global Positioning System"(GPS), Galileo, \Global Monitoring for Environment and Security"(GMES), Google Earth, etc. Actualment, la demanda i el consum de geoinformaci o est a incrementant i, a m es a m es, aquesta ha de ser precisa, exacta, actualitzada i assequible. Amb l'objectiu d'acomplir aquests requisits t ecnics i, en general, la demanda del mercat, la ind ustria i l' ambit acad emic estan introduint un darrera l'altre sistemes d'imatgeria, plataformes a eries i plataformes satel.litals. Per o alhora, aquests sistemes d'adquisici o introdueixen nous problemes com el calibratge i l'orientaci o de sensors, la navegaci o de les plataformes (de manera precisa i exacta segons el seu rendiment), la combinaci o de diferents tipus de sensors, la integraci o de dades auxiliars que provenen de diverses fonts, aspectes temporals com la gravaci o \cont nua"en el temps dels sensors, la feble geometria d'alguns d'ells, etc. Alguns d'aquests problemes es poden resoldre amb els m etodes i estrat egies actuals, sovint afegint pegats, per o la majoria no es poden resoldre amb els m etodes vigents o no es poden resoldre amb els m etodes vigents amb fiabilitat i robustesa. Aquesta tesi presenta les abstraccions i generalitzacions necess aries que permeten desenvolupar la propera generaci o d'ajustos de xarxes i m etodes d'estimaci o amb l'objectiu de resoldre aquests problemes. A m es, basada en aquestes idees, s'ha desenvolupat la principal eina d'aquesta recerca: la plataforma de software \Generic Extensible Network Approach"(GENA). L'objectiu d'aquesta recerca es establir les bases met odiques d'un concepte sistem atic per l'orientaci o i el calibratge de sensors aeris i provar la seva validesa amb nous models i aplicacions. Aix , en primer lloc, prenent dist ancia sobre el que s'ha fet tradicionalment i tenint en compte tot el que ens ofereix la tecnologia INS/GNSS, aquesta tesi genera un m etode per l'explotaci o dels sistemes INS/GNSS en l'orientaci o i el calibratge de sensors aeris. I, en segon lloc, s'han proposat i testejat amb dades reals alguns models que conformen aquest concepte, com per exemple, l' us de temps, posici o i actitud donats pel sistema INS/GNSS en mode relatiu (eliminant la necessitat dels par ametres d'absorci o d'errors INS/GNSS o la matriu d'orientaci o relativa IMU-sensor), l' us de temps, posici o, velocitat i actitud pel calibratge de temps (utilitzant aix la soluci o completa que donen els sistemes INS/GNSS per lligar les dimensions espacial i temporal) o reduir el nombre de mesures de l'orientaci o integrada de sensors tradicional, duent a terme la proposta \fast aerotriangulation", Fast AT. Aquesta recerca est a presentada a la tesi com un compendi d'articles. Aix doncs, els resultats de la tesi no s on nom es el document de la tesi en si mateix i les publicacions, hi ha tamb e un software comercial i models i aplicacions que validen el m etode proposat i representen un nou panorama per l'orientaci o i el calibratge de sensors aeris.En la actualidad, el mercado de la geom atica est a valorado en unos 30 billones de euros. Tras el crecimiento de dicho mercado, se hallan nuevas tecnologias, proyectos y aplicaciones, como por ejemplo, \Global Positioning System"(GPS), Galileo, \Global Monitoring for Environment and Security"(GMES), Google Earth, etc. Hoy en d a, la demanda y el consumo de geoinformaci on est a increment andose y, adem as, dicha informaci on debe ser precisa, exacta, actualizada y asequible. Intentando cumplir estos requisitos t ecnicos y, en general, la demanda del mercado, la industria y el ambito acad emico est an introduciendo uno tras otro sistemas de imagen, plataformas a ereas y plataformas satelitales. Pero a su vez, estos sistemas de adquisici on introducen nuevos problemas como la calibraci on y la orientaci on de sensores, la navegaci on de las plataformas (debe ser precisa y exacta teniendo en cuenta su rendimiento particular), la combinación de diferentes tipos de sensor, la integraci on de datos auxiliares que proceden de diversas fuentes, aspectos temporales como la grabaci on \continua" en el tiempo de los sensores, la d ebil geometr a de algunos de ellos, etc. Algunos de estos problemas pueden resolverse con los m etodos y estrategias actuales, generalmente aplicando parches, pero la mayor a no se pueden resolver con los m etodos vigentes o no se pueden resolver con los m etodos vigentes con fi abilidad y robustez. Esta tesis presenta las abstracciones y generalizaciones necesarias que permiten desarrollar la pr oxima generaci on de ajustes de redes y m etodos de estimaci on con el objetivo de resolver estos problemas. Es m as, basada en estas ideas, se ha desarrollado la herramienta principal de esta investigaci on: la plataforma de software \Generic Extensible Network Approach"(GENA). El objetivo de esta investigaci on es establecer las bases met odicas de un concepto sistem atico para la orientaci on y la calibraci on de sensores a ereos, y probar su validez con nuevos modelos y aplicaciones. As pues, en primer lugar, distanci andonos de lo que tradicionalmente se ha realizado y considerando lo que la tecnolog a INS/GNSS nos ofrece, esta tesis crea un m etodo para la explotaci on de los sistemas INS/GNSS en la orientaci on y la calibraci on de sensores a ereos. Y, en segundo lugar, se proponen y testean con datos reales algunos modelos que constituyen este concepto, como por ejemplo, el uso de tiempo, posici on y actitud dados por el sistema INS/GNSS en modo relativo (eliminando la necesidad de los par ametros de absorci on de errores INS/GNSS o la matriz de orientaci on relativa IMU-sensor), el uso de tiempo, posici on, velocidad y actitud para la calibraci on temporal (utilizando as la soluci on completa que dan los sistemas INS/GNSS para enlazar las dimensiones espacial y temporal) o reducir el n umero de medidas de la orientaci on integrada de sensores tradicional, llevando a cabo la propuesta \fast aerotriangulation", Fast AT. Esta investigaci on est a presentada en la tesis como un compendio de art culos. Resumiendo, los resultados de la tesis no son s olo el documento de la tesis en sí mismo y las publicaciones, existe tambi en un software comercial y modelos y aplicaciones que validan el m etodo propuesto y presentan un nuevo panorama para la orientaci on y la calibraci on de sensores a ereos.The geomatic market has an estimated value of some 30 thirty trillion euros. Behind this growing market, there are new technologies, projects and applications like Global Positioning System (GPS), Galileo, Global Monitoring for Environment and Security (GMES), Google Earth, etc. Modern society is increasingly demanding and consuming geoinformation that must be precise, accurate, up-to-date and affordable. In an attempt to meet these technical requirements and general market demand, industry and academia are introducing one imaging system, airborne platform and satellite platform after another. These acquisitions are introducing new problems such as calibration and orientation of the sensors, navigation of the platforms (with an accurate and precise processing of their individual performances), combination of different types of sensors, integration of auxiliary data provided from various sources, temporal issues of the ¿continuously¿ recording sensors, weak geometry of some sensors, etc. Some of the previous problems can be solved with current methods and strategies, oftentimes with a dose of patchwork. However, the vast majority of these problems cannot be solved with the current methods, or at least not with a like degree of robustness and reliability. This thesis presents the abstractions and generalizations needed to facilitate the development of the next generation of network adjustment and estimation methods that will make it possible to solve these problems. Moreover, the main tool of this research is a commercial software platform, ¿Generic Extensible Network Approach' (GENA), based on the proposed network approach. The goal of this research is to establish a methodical basis of a systematic approach to airborne sensor orientation and calibration and to prove its validity with newly-developed models and applications. On one hand, viewing the traditional DiSO and ISO from a distance and considering the possibilities that the INS/GNSS technology offers, this thesis generates a method to exploit the INS/GNSS systems for airborne sensor orientation and calibration. On the other hand, several models that constitute this method are proposed and tested with independent actual data sets; for example, the use of INS/GNSS-derived time, position and attitude in relative mode (avoiding the need for GNSS linear shift parameters, that absorb the INS/GNSS errors, or the relative orientation IMU-to-sensor, boresight, matrix), the use of INS/GNSS-derived time, position, velocity and attitude for time calibration (exploiting the full solution of the INS/GNSS systems to link the space and time dimensions) or the measurement reduction of the traditional integrated sensor orientation to perform the proposed "fast aerotriangulation", or Fast AT. This research is presented in the thesis as compiled papers. Therefore, the results of this thesis are not only the thesis document itself and a number of publications, but also a commercial software platform and models and applications that validate the proposed method and present a new panorama for airborne sensor orientation and calibration

UAV photogrammetry ground control reductions using GNSS

Ph. D. Thesis.Unmanned aerial vehicles (UAVs) are now well-established as platforms for photogrammetric data acquisition. Their advantages, particularly over conventional manned aerial platforms, relate to their low cost, ease of use, rapid deployability and low-level flying for the collection of centimetre-level spatial resolution imagery. Coupled with recent innovations in photogrammetry and computer vision, UAVs equipped with consumer grade digital cameras are now frequently used to generate centimetre-resolution and accuracy mapping products, such as dense point clouds, digital elevation models and orthomosaics. Despite the efficiency of UAV data acquisition, the continued need for ground control implementation for photogrammetric image orientation remains a substantial workflow constraint. In addition to the associated costs, ground control must be implemented strategically, and usually extensively, to ensure photogrammetric products meet the accuracy requirements of large scale mapping, which may or may not be possible given constraints of the intended application. This research uses high precision, UAV-based GNSS (Global Navigation Satellite System) positioning techniques to substantially reduce ground control requirements by directly determining UAV image positions with centimetre-level accuracy and precision. The Precise Point Positioning (PPP) technique is applied and can yield centimetre-level planimetric and decimetre height accuracy photogrammetric mapping without GCPs, whilst the height accuracy can be improved to the centimetre-level using a single GCP. Unlike the standard relative GNSS positioning technique, PPP alleviates all spatial operating constraints associated with the installation and use of a local ground-based GNSS reference station, or the need to operate within the bounds of a permanent GNSS reference station network. Such a workflow simplifies operational logistics, and enables large-scale photogrammetric mapping from UAVs in even the most remote and challenging geographic locations globally. The approach was tested on 11 fixed wing UAV datasets, acquired at two sites in Northumberland, north-east England, which had varying ground control configurations. UAV flight durations, meaning time between launch and landing, were 12-42 minutes. It is shown that the main limitation of UAV-based PPP application is the inherent possibility of GNSS cycle slips and limited observation spans that inhibit the convergence of float ambiguity estimates. Although PPP camera position estimates were biased in such cases, GCPs were still minimised due to the retained precision of the PPP camera position estimates and constraints on the image block.EPSR