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Cobertura aérea nacional RAF47: recuperação radiométrica e triangulação
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Um conjunto de fotografias aéreas foi oferecido aos Serviços Cartográficos do Exército, em 1948, pela British Royal Air Force. Os recipientes metálicos, onde se encontram guardados os rolos de filme fotográfico, têm seguido a instituição em todas as suas mudanças de instalações. Actualmente, esta cobertura aérea pode ser encontrada numa sala própria, com um sistema de refrigeração, nas instalações do Instituto Geográfico do Exército. A fim de obter alguma informação sobre o voo, foi realizada uma pesquisa. Foram encontrados vários dados relativos ao avião, à câmara e às lentes, incluindo um valor para a constante da câmara. Uma metodologia para recuperar as propriedades radiométricas e geométricas das imagens foi aplicada sobre um pequeno conjunto de fotografias. Devido à idade, à qualidade das lentes e às “aventuras” a que as fotografias do RAF47 têm sido sujeitas, a qualidade radiométrica das imagens está longe de ser a indicada para a realização de uma triangulação automática. Para ultrapassar este problema, foi desenvolvido um programa para possibilitar a uniformização da luminosidade das fotografias. Quanto à recuperação geométrica, foi encontrado um problema muito grave: a inexistência de certificado de calibração da câmara. Várias experiências foram realizadas para encontrar a forma correcta de realizar a orientação interna das imagens e foi construído um programa para detectar automaticamente as marcas fiduciais. As coordenadas foto dos pontos de passagem e dos pontos de ligação foram obtidas através de uma triangulação automática. Como a área geográfica estudada neste projecto testemunhou muitas alterações ao nível do uso do solo nos últimos 62 anos, os pontos fotogramétricos não foram adquiridos através de um levantamento topográfico. Como alternativa, foram utilizados pontos fotogramétricos documentados em antigos cadernos de campo. Os parâmetros de orientação externa foram calculados através de uma triangulação em bloco por feixes perspectivos, onde também foram determinados os parâmetros de auto-calibração. Estes permitiram a construção de um modelo de distorção das lentes usadas. Foi realizado um controlo de qualidade dos resultados obtidos. Os pontos fotogramétricos que não foram usados na triangulação foram medidos nos modelos estereoscópicos formados a partir das fotos orientadas. Os valores foram utilizados para estudar o comportamento da incerteza e do deslocamento dos pontos ao longo da cobertura. Os dados adquiridos durante a pesquisa e a recuperação geométrica foram reunidos numa base de dados foto-geográfica, onde poderão ser facilmente encontrados pelos interessados nas fotografias do voo RAF47.
A set of aerial photographs was given to the Serviços Cartográficos do Exército in 1948 by the British Royal Air Force. The metal bins where the photographic film is stored have followed the institute in all its facilities changes. In the present days this set can be found in a special refrigerated room in the facilities of the Instituto Geográfico do Exército. A research was made in order to get some information about the flight. Many interesting data related to the plane, camera and lenses have been found, including a value for the camera focal length. A methodology to recover the radiometric and the geometric properties of the images was applied in a small set of photographs. Due to age, poor quality lenses and the many “adventures” that the photographs of RAF47 have gone through, the radiometric quality of the images is far from being suitable for an automatic triangulation. To overcome this problem, a program has been developed, so that it becomes possible to turn the photographs background luminosity uniform. As for the geometric recovery of the photos, a huge problem had to be solved: the inexistence of the camera calibration certificate. A lot of tests were made in order to find the correct way to perform the interior orientation and a program was built to automatically find the fiducial marks of the photographs. The photo coordinates of the pass points and of the tie points were achieved through an automatic triangulation. As the geographic area studied in this project witnessed a lot of land use changes in the last 62 years, the ground control points were not obtained by a topographic survey. Instead, the coordinates of ground control points from old field notes were used. The exterior orientation parameters were calculated in a bundle block adjustment where the additional parameters for self-calibration were also determined, allowing a lens distortion model to be built. A quality control to check the results obtained in the last step was made. Some of the ground control points which were not used in the bundle block adjustment were measured in the stereoscopic models built through the oriented photographs. These values were used to study the behavior of uncertainty and point displacements throughout the photographic block. All the data achieved in the research and during the geometric recovery were joined in a photo-geographic database where they will be able to be easily found by all the people interested in using the photographs from the RAF47 flight.
A set of aerial photographs was given to the Serviços Cartográficos do Exército in 1948 by the British Royal Air Force. The metal bins where the photographic film is stored have followed the institute in all its facilities changes. In the present days this set can be found in a special refrigerated room in the facilities of the Instituto Geográfico do Exército. A research was made in order to get some information about the flight. Many interesting data related to the plane, camera and lenses have been found, including a value for the camera focal length. A methodology to recover the radiometric and the geometric properties of the images was applied in a small set of photographs. Due to age, poor quality lenses and the many “adventures” that the photographs of RAF47 have gone through, the radiometric quality of the images is far from being suitable for an automatic triangulation. To overcome this problem, a program has been developed, so that it becomes possible to turn the photographs background luminosity uniform. As for the geometric recovery of the photos, a huge problem had to be solved: the inexistence of the camera calibration certificate. A lot of tests were made in order to find the correct way to perform the interior orientation and a program was built to automatically find the fiducial marks of the photographs. The photo coordinates of the pass points and of the tie points were achieved through an automatic triangulation. As the geographic area studied in this project witnessed a lot of land use changes in the last 62 years, the ground control points were not obtained by a topographic survey. Instead, the coordinates of ground control points from old field notes were used. The exterior orientation parameters were calculated in a bundle block adjustment where the additional parameters for self-calibration were also determined, allowing a lens distortion model to be built. A quality control to check the results obtained in the last step was made. Some of the ground control points which were not used in the bundle block adjustment were measured in the stereoscopic models built through the oriented photographs. These values were used to study the behavior of uncertainty and point displacements throughout the photographic block. All the data achieved in the research and during the geometric recovery were joined in a photo-geographic database where they will be able to be easily found by all the people interested in using the photographs from the RAF47 flight.
Descrição
Tese de mestrado, Engenharia Geográfica, Universidade de Lisboa, Faculdade de Ciências, 2009
Palavras-chave
Fotografias aéras antigas Recuperação radiométrica Orientação interna Triangulação por feixes perspectivos Base de dados foto-geográfica Teses de mestrado - 2009