MEASURING PHOTOGRAMMETRIC CONTROL TARGETS IN LOW CONTRAST IMAGES

This paper presents an experimental assessment of photogrammetric targets and subpixel location techniques to be used with low contrast images such as images acquired by hyperspectral frame cameras. Eight different target patterns of varying shape, background, and size were tested. The aim was to identify an optimum distinctive pattern to serve as control point in aerial surveys of small areas using hyperspectral cameras when natural points are difficult to find in suitable areas. Three automatic techniques to identify the target point of interest were compared, which were weighted centroid, template matching, and line intersection. For assessment, hyperspectral images of the set of targets were collected in an outdoor 3D terrestrial calibration field. RGB images were also acquired for reference and comparison. Experiments were conducted to assess the accuracy at the sub-pixel level. Bundle adjustment with several images was used, and vertical and horizontal distances were directly measured in the field for verification. An experiment with aerial flight was also performed to validate the chosen target. The analysis of residuals and discrepancies indicated that a circular target is best suited as the ground control in aerial surveys, considering the condition in which the target appears with few pixels in the image

A LIGHTWEIGHT UAV-BASED LASER SCANNING SYSTEM FOR FOREST APPLICATION

Lightweight Unmanned Aerial Vehicles (UAVs) have become a cost effective alternative for studies which use aerial Remote Sensing with high temporal frequency requirements for small areas. Laser scanner devices are widely used for rapid tridimensional data acquisition, mainly as a complementary data source to photogrammetric surveying. Recent studies using laser scanner systems onboard UAVs for forestry inventory and mapping applications have presented encouraging results. This work describes the development and accuracy assessment of a low cost mapping platform composed by an Ibeo Lux scanner, a GNSS (Global Navigation Satellite System) antenna, an Inertial Navigation System Novatel Span-IGM-S1, integrating a GNSS receiver and an IMU (Inertial Measurement Unit), a Raspberry PI portable computer and an octopter UAV. The system was assessed in aerial mode using an UAV octopter developed by SensorMap Company. The resulting point density in a plot with trees concentration was also evaluated. The point density of this device is lower than conventional Airborne Laser Systems but the results showed that altimetric accuracy with this system is around 30 cm, which is acceptable for forest applications. The main advantages of this system are their low weight and low cost, which make it attractive for several applications

Data Product Specification Proposal for Architectural Heritage Documentation with Photogrammetric Techniques: A Case Study in Brazil

peer reviewedPhotogrammetric documentation can provide a sound database for the needs of architectural heritage preservation. However, the major part of photogrammetric documentation production is not used for subsequent architectural heritage projects, due to lack of knowledge of photogrammetric documentation accuracy. In addition, there are only a few studies with rigorous analysis of the requirements for photogrammetric documentation of architectural heritage. In particular, requirements focusing on the geometry of the models generated by fully digital photogrammetric processes are missing. Considering these needs, this paper presents a procedure for architectural heritage documentation with photogrammetric techniques based on a previous review of existing standards of architectural heritage documentation. The data product specification proposed was elaborated conforming to ISO 19131 recommendations. We present the procedure with two case studies in the context of Brazilian architectural heritage documentation. Quality analysis of the produced models were performed considering ISO 19157 elements, such as positional accuracy, logical consistency and completeness, meeting the requirements. Our results confirm that the proposed requirements for photogrammetric documentation are viable

A AULA INAUGURAL DO CURSO DE GEOMETRIA APLICADA ÀS ARTES NO CONSERVATÓRIO IMPERIAL DE ARTES E OFÍCIOS

Nesta comunicação, apresenta-se a tradução do texto integral da aula inaugural do Coronel Aimé Laussedat (1819-1907), professor suplente no Conservatoire Impérial des Arts et Métiers (antigo nome do CNAM), comentado pelo autor na versão original, publicado pela Associação Francesa de Topografia (revista XYZ vol. 133 4° trimestre 2012, pag. 57-64), traduzido por Laurent Polidori e Antonio M. G. Tommaselli

A STUDY ON THE EFFECTS OF VIEWING ANGLE VARIATION IN SUGARCANE RADIOMETRIC MEASURES

Remote Sensing techniques, such as field spectroscopy provide information with a large level of detail about spectral characteristics of plants enabling the monitoring of crops. The aim of this study is to analyze the influence of viewing angle in estimating the Bidirectional Reflectance Distribution Function (BRDF) for the case of sugarcane. The study on the variation of the spectral reflectance profile can help the improvement of algorithms for correction of BRDF in remote sensing images. Therefore, spectral measurements acquired on nadir and different off-nadir view angle directions were considered in the experiments. Change both anisotropy factor and anisotropy index was determined in order to evaluate the BRDF variability in the spectral data of sugarcane. BRDF correction was applied using the Walthall model, thus reducing the BRDF effects. From the results obtained in the experiments, the spectral signatures showed a similar spectral pattern varying mainly in intensity. The anisotropy factor which showed a similar pattern in all wavelengths. The visual analysis of the spectral reflectance profile of sugarcane showed variation mainly in intensity at different angles. The use of Walthall model reduced the BRDF effects and brought the spectral reflectance profiles acquired on different viewing geometry close to nadir viewing. Therefore, BRDF effects on remote sensing data of vegetation cover can be minimized by applying this model. This conclusion contributes to developing suitable algorithms to produce radiometrically calibrated mosaics with remote sensing images taken by aerial platforms

EXPERIMENTAL ASSESSMENT OF TECHNIQUES FOR FISHEYE CAMERA CALIBRATION

Fisheye lens cameras enable to increase the Field of View (FOV), and consequently they have been largely used in several applications like robotics. The use of this type of cameras in close-range Photogrammetry for high accuracy applications, requires rigorous calibration. The main aim of this work is to present the calibration results of a Fuji Finepix S3PRO camera with Samyang 8mm fisheye lens using rigorous mathematical models. Mathematical models based on Perspective, Stereo-graphic, Equi-distant, Orthogonal and Equi-solid-angle projections were implemented and used in the experiments. The fisheye lenses are generally designed following one of the last four models, and Bower-Samyang 8mm lens is based on Stereo-graphic projection. These models were used in combination with symmetric radial, decentering and affinity distortion models. Experiments were performed to verify which set of IOPs (Interior Orientation Parameters) presented better results to describe the camera inner geometry. Collinearity mathematical model, which is based on perspective projection, presented the less accurate results, which was expected because fisheye lenses are not designed following the perspective projection. Stereo-graphic, Equi-distant, Orthogonal and Equi-solid-angle projections presented similar results even considering that Bower-Samyang fisheye lens was built based on Stereo-graphic projection. The experimental results also demonstrated a small correlation between IOPs and EOPs (Exterior Orientation Parameters) for Bower-Samyang lens

REGISTRO SEMIAUTOMÁTICO ENTRE IMAGENS INFRAVERMELHAS E RGB COLETADAS POR UM PAR DE CÂMARAS DIGITAIS

A utilização de imagens adquiridas por sensores CCDs de médio formato, em plataformas aéreas, é uma alternativa para  a redução de custos de projetos de aerolevantamento. Porém, a utilização de sensores que captem somente a banda do visível (RGB) restringe algumas aplicações, tornando-se relevante integrar um sensor adicional que capte o infravermelho próximo (IR). No mercado há várias soluções para a aquisição simultânea de várias bandas espectrais. Uma alternativa que possibilita uma redução nos custos de integração é coletar as bandas RGB com uma câmara e a infravermelha com uma segunda câmara. É necessário, entãoregistrar as imagens, o que implica em determinar um conjunto de pontos ou feições correspondentes, calcular uma função de mapeamento polinomial e reamostrar uma das imagens. Um dos problemas mais críticos é a determinação de  correspondência entre as imagens, devido às diferenças  radiométricas entre as imagens. Neste trabalho são utilizadas técnicas de detecção de pontos de interesse e é proposta umafunção de correspondência usando as diferenças nas magnitudes e direções dos gradientes de intensidade entre as imagens RGB e IR. Foram realizados vários experimentos com a técnica proposta, indicando que é possível utilizar esta técnica obtendo-se erros residuais inferiores a 1,5 pixel

UM MÉTODO PARA A CONEXÃO E APROXIMAÇÃO POLIGONAL DE ELEMENTOS DE BORDAS EM IMAGENS DIGITAIS

Este trabalho apresenta um método para a conexão de pixels de borda, com o objetivo de segmentar as retas definidas pelas descontinuidades nos tons de cinza em imagens digitais. Este método é baseado na técnica de Varredura e Rotulação, em relação à qual foram propostos vários passos adicionais para a efetiva extração de feições retas. O método também possui uma alternativa baseada no processo de perseguição de contorno. Todas as modificações foram desenvolvidas após estudos sobre imagens aéreas reais, sendo apresentados resultados obtidos com dados sintéticos e dados reais. A method for edge pixel connection and straight-line segmentation in digital images Abstract In this paper a method for edge pixel connection is presented, aiming at the segmentation of the straight-lines defined by gray level discontinuities in digital images. This proposed method is based on the Scan and Label technique, with was improved with several additional steps aiming at effective straight line extraction. An alternative based on the edge following technique was also implemented. All the improvements were developed after extensive experiments with real aerial images. Some results obtained with synthetic and real data are presented

DETECÇÃO E AFINAMENTO DE BORDAS EM DIREÇÕES PREVIAMENTE CONHECIDAS

This work presents a study on the generation of digital masks aiming at edge detection with previously known directions. This solution is important when edge direction is available either from a direction histogram or from a prediction based on camera and object models. A modification in the non-maximum suppression method of thinning is also presented enabling the comparison of local maxima for any edge directions. Results with a synthetic image and with crops of a CBERS satellite images are presented showing an example with its application in road detection, provided that directions are previously known.Este trabalho apresenta um método para a construção de filtros para detecção de bordas que apresentam uma maior resposta em direções previamente estabelecidas. Esta solução é importante quando se deseja extrair linhas cuja direção é previamente conhecida, tanto a partir de um histograma de direções predominantes, quanto pela predição com base nos modelos de câmara e do objeto. Apresenta-se também uma modificação no método de afinamento por supressão não–máxima, permitindo o tratamento de bordas com qualquer direção. Por fim, são apresentados alguns resultados com uma imagem sintética e com recortes de imagens orbitais CBERS, mostrando exemplos de aplicação dos filtros propostos para detectar bordas de rodovias, cujas direções são conhecidas