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

Um modelo alternativo à equaçao de colinearidade utilizando feições retas

Orientador: Joao Bosco LugnaniDissertaçao (mestrado) -Universidade Federal do Paraná. Curso de Pós-Graduaçao em Ciencias GeodésicasResumo: O objetivo deste trabalho é propor um modelo matemático que estabeleça uma relação funcional entre feições Retas no espaço objeto e espaço imagem, prescindindo da correspondência ponto a ponto. Este modelo matemático baseia-se na equivalência entre parêmetros do plano determinado pela feição-imagem e pelo C.P., no espaço imagem, e parâmetros do plano determinado pela feição e pelo C.P. no espaço objeto. E apresentado o desenvolvimento da metodologia visando a aplicação do modelo nos problemas de Resseção Espacial e Formação Analítica de Modelos. Os resultados práticos obtidos, usando dados simulados, são apresentados e discutidos, mostrando que o modelo dos "planos equivalentes" funciona plenamente.Abstract:The aim of this theele Is to suggest a mathematical model in order to establish a funtional relationship between straight features in object and image space, without necessity of point to point correspondence. This mathematical model Is based on the equivalence between definition parameters from the planes determined by each straight feature - either In the Image and in the object space - and the Perspective Center (P.C.). It is presented the development of the methodology aiming the application of this mathematical model to the resection and analytical stereomode 1 formation problems. The obtained practical results, using simulate data, are presented and discussed, showing that the "equivalent planes mathematical model" works succesfully