Parameterising internal camera geometry with focusing distance

A study on the variation of internal camera geometry (principal distance, principal point position and lens distortion parameters) with different focus distances has been conducted. Results demonstrate that variations of parameters are continuous and predictable, allowing a new way to describe internal camera geometry. The classical constant parameters, c, x p , y p , K 1 , K 2 , P 1 and P 2 , are replaced by continuous functions, c(γ), x p (γ), y p (γ), K 1 (γ), K 2 (γ), P 1 (γ) and P 2 (γ), where γ is a variable describing the focus position. Incorporation of γ as a metadata tag (for example, Exif header) of a photograph jointly with a parameterised definition of camera geometry would allow full use of the autofocus camera function; enabling maximum effective depth of field, better match of the plane of focus with the object’s position and higher reliability. Additionally, conducted tests suggest the parameterised definition of internal geometry could help to locate and correct linear dependences between adjusted parameters, potentially improving the precision and accuracy of calibration

Assessment of low-cost GPS receiver accuracy and precision in forest environments

P. 159-167Selecting the apppropriate receiver is an issue when a major portion of global positioning system (GPS) data collection is below forest canopies. This study compares four low-cost GPS receivers, in order to determine the most suitable receiver for position assessment under differnt forest canopy covers, in terms of ease of use, accuracy, and relability. A total of 33 positional assessments were gathered per receiver, plot, and method, in 18 forest location.S

Evaluación de errores en el posicionamiento con receptores GPS de doble frecuencia bajo cubierta arbolada de Pinus dadiata D.Don

El uso de receptores GPS en el ámbito forestal se ha generalizando y sus aplicaciones son muy variadas (localización de parcelas de inventario, guiado de maquinaria forestal, uso recreativo, etc.). El objetivo de este trabajo fue evaluar la precisión y exactitud del posicionamiento GPS bajo la cubierta de masas de Pinus radiata. Para ello se identificaron 12 puntos de muestreo en parcelas con 4 densidades diferentes (3 parcelas en cada nivel de densidad) y 1 punto en una zona despejada para poder comparar la influencia de la cobertura arbórea. En cada punto se hicieron observaciones estáticas por un período de una hora. Se determinaron las coordenadas X,Y,Z para cada segundo, se calcularon las exactitudes y se identificaron las distribuciones teóricas que mejor se ajustaban a los valores de exactitud obtenidos para cada tipo de masa. Del análisis de los resultados se pude deducir que: i) las variables dasométricas que más influyen en la exactitud planimétrica son el número de pies por ha (N) y el diámetro medio cuadrático (dg); ii) la probabilidad de que la exactitud planimétrica sea menor de 1 m y de que la exactitud altimétrica sea menor de 3 m es del 70%. Los resultados obtenidos permitirán planificar más adecuadamente las observaciones con receptores GPS en zonas arboladas.The use of GPS receivers in forestry has been widespread and this technology is used for location of inventory plots, guided forest machinery, recreational use and navigation, etc. The aim objective of this study was to evaluate the accuracy and positioning accuracy of dual-frequency GPS receivers under tree canopy of Pinus radiate stands. In order to compare the influence of tree canopy in the GPS positioning, 12 points were established in 4 stands with different densities (three plots of each density level). An additional point was located in a nearby area without trees. At each point, static observations were made for a period of one hour and the coordinates X,Y,Z were calculated for each second. Precisions, accuracies and theoretical distributions were identified for each type of stands. The stand variables related to horizontal accuracy were the number of trees per hectare (N), the Hart-Becking index (IH) and the quadratic mean diameter (dg). The probability that both the horizontal accuracy is less than 1 m and the vertical accuracy is less than 3 m is 70%. The results obtained will allow a more adequately planning of observations with GPS receivers in forest areas

Measuring glacier surface roughness using plot-scale, close-range digital photogrammetry

Glacier roughness at sub-metre scales is an important control on the ice surface energy balance and has implications for scattering energy measured by remote-sensing instruments. Ice surface roughness is dynamic as a consequence of spatial and temporal variation in ablation. To date, studies relying on singular and/or spatially discrete two-dimensional profiles to describe ice surface roughness have failed to resolve common patterns or causes of variation in glacier surface morphology. Here we demonstrate the potential of close-range digital photogrammetry as a rapid and cost-effective method to retrieve three-dimensional data detailing plot-scale supraglacial topography. The photogrammetric approach here employed a calibrated, consumer-grade 5 Mpix digital camera repeatedly imaging a plotscale (≤25m2) ice surface area on Midtre Lovénbreen, Svalbard. From stereo-pair images, digital surface models (DSMs) with sub-centimetre horizontal resolution and 3mm vertical precision were achieved at plot scales ≤4m2. Extraction of roughness metrics including estimates of aerodynamic roughness length (z0) was readily achievable, and temporal variations in the glacier surface topography were captured. Close-range photogrammetry, with appropriate camera calibration and image acquisition geometry, is shown to be a robust method to record sub-centimetre variations in ablating ice topography. While the DSM plot area may be limited through use of stereo-pair images and issues of obliquity, emerging photogrammetric packages are likely to overcome such limitations

Metric potential of a 3D measurement system based on digital compact cameras

P. 4178-4194This paper presents an optical measuring system based on low cost, hogh resolution digital cameras. Once the cameras are synchronised, the portable and adjuntable system can be used to observe living beings, bodies in motion, or deformations of very different sizes. Each of the cameras has been modelled individually and studied with regard to the photogrammetric potential of the system. We have investigated the photogrammetric precision obtained from the crossing of rays, the repeatability of results, and the accuracy of the coordinates obtained. Systematic and random errors are identified in validity assessment of the definition of the precision of the system from crossing of rays or from marking residuals in images. The results have clearly demonstrated the capability of a low-cost multiple-camera system to measure with sub-millimetre precision.S

Geometric stability and lens decentering in compact digital cameras

P. 1553-1572A study on the geometric stability and decentering present in sensor-lens systems of six identical compact digital cameras has been conducted. With regard to geometrical stability, the variation of internal geometry parameters (principal distance, principal point position and distortion parameters) was considered. With regard to lens decentering, the amount of radical and tangential displacement resulting from decentering distortion was related with the precision of the camera and with the offset of the principal point from the geometric center of the sensor. The study was conducted with data obtained after 372 calibration processes (62 per camera). The tests were performed for each camera in three situations: during continuous use of the cameras, after camera power off/on and after the full extension and retraction of the zoom-lens.S

Geometric Stability and Lens Decentering in Compact Digital Cameras

P. 1553-1572A study on the geometric stability and decentering present in sensor-lens systems of six identical compact digital cameras has been conducted. With regard to geometrical stability, the variation of internal geometry parameters (principal distance, principal point position and distortion parameters) was considered. With regard to lens decentering, the amount of radial and tangential displacement resulting from decentering distortion was related with the precision of the camera and with the offset of the principal point from the geometric center of the sensor. The study was conducted with data obtained after 372 calibration processes (62 per camera). The tests were performed for each camera in three situations: during continuous use of the cameras, after camera power off/on and after the full extension and retraction of the zoom-lens. Additionally, 360 new calibrations were performed in order to study the variation of the internal geometry when the camera is rotated. The aim of this study was to relate the level of stability and decentering in a camera with the precision and quality that can be obtained. An additional goal was to provide practical recommendations about photogrammetric use of such cameras.S

Using Unmanned Aerial Vehicles in Postfire Vegetation Survey Campaigns through Large and Heterogeneous Areas: Opportunities and Challenges

17 p.This study evaluated the opportunities and challenges of using drones to obtain multispectral orthomosaics at ultra-high resolution that could be useful for monitoring large and heterogeneous burned areas. We conducted a survey using an octocopter equipped with a Parrot SEQUOIA multispectral camera in a 3000 ha framework located within the perimeter of a megafire in Spain. We assessed the quality of both the camera raw imagery and the multispectral orthomosaic obtained, as well as the required processing capability. Additionally, we compared the spatial information provided by the drone orthomosaic at ultra-high spatial resolution with another image provided by theWorldView-2 satellite at high spatial resolution. The drone raw imagery presented some anomalies, such as horizontal banding noise and non-homogeneous radiometry. Camera locations showed a lack of synchrony of the single frequency GPS receiver. The georeferencing process based on ground control points achieved an error lower than 30 cm in X-Y and lower than 55 cm in Z. The drone orthomosaic provided more information in terms of spatial variability in heterogeneous burned areas in comparison with theWorldView-2 satellite imagery. The drone orthomosaic could constitute a viable alternative for the evaluation of post-fire vegetation regeneration in large and heterogeneous burned areasS

Problem Based Learning (PBL) and E-learning in geodetic engineering, cartography and surveying education in the European Higher Education Area (EHEA) frame. A case study in the University of Leon (Spain): experiences and results

The concepts and strategies defined in the Bologna Process to develop a European Higher Education Area, involve a change in the educative programs, wich have to be adapted to innovative teaching and learning processes based on achieving specific knowledge according to the professional field of work. Thus, the method has to be focused in the learning process and not in the teaching process. Probelm Based Learning emphasises learning activities which are student-centred,interdisciplinary, autehentic, collaborative and foster higher order thinkin

Detecting and Modeling the Changes of Land Use/Cover for Land Use Planning in Da Nang City, Viet Nam

The geometrical accuracy of georeferenced digital surfacemodels (DTM) obtained fromimages captured bymicro-UAVs and processed by using structure frommotion (SfM) photogrammetry depends on several factors, including flight design, camera quality, camera calibration, SfM algorithms and georeferencing strategy. This paper focusses on the critical role of the number and location of ground control points (GCP) used during the georeferencing stage. A challenging case study involving an area of 1200+ ha, 100+ GCP and 2500+ photos was used. Three thousand, four hundred and sixty-five different combinations of control points were introduced in the bundle adjustment, whilst the accuracy of the model was evaluated using both control points and independent check points. The analysis demonstrates how much the accuracy improves as the number of GCP points increases, as well as the importance of an even distribution, how much the accuracy is overestimated when it is quantified only using control points rather than independent check points, and how the ground sample distance (GSD) of a project relates to the maximum accuracy that can be achieved