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

High-Resolution Drone-Acquired RGB Imagery to Estimate Spatial Grape Quality Variability

[EN] Remotesensing techniques can help reduce time and resources spent collecting samples of crops and analyzing quality variables. The main objective of this work was to demonstrate that it is possible to obtain information on the distribution of must quality variables from conventional photographs. Georeferenced berry samples were collected and analyzed in the laboratory, and RGB images were taken using a low-cost drone from which an orthoimage was made. Transformation equations were calculated to obtain absolute reflectances for the different bands and to calculate 10 vegetation indices plus two new proposed indices. Correlations for the 12 indices with values for 15 must quality variables were calculated in terms of Pearson’s correlation coefficients. Significant correlations were obtained for 100-berries weight (0.77), malic acid (−0.67), alpha amino nitrogen (−0.59), phenolic maturation index (0.69), and the total polyphenol index (0.62), with 100-berries weight and the total polyphenol index obtaining the best results in the proposed RGB-based vegetation index 2 and RGB-based vegetation index 3. Our findings indicate that must variables important for the production of quality wines can be related to the RGB bands in conventional digital images, potentially improving and aiding management and increasing productivity.SIEducation Department of the Junta de Castilla y León-Spai

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

Total Soluble Solids in Grape Must Estimation Using VIS-NIR-SWIR Reflectance Measured in Fresh Berries

[EN] Total soluble solids (TSS) is a key variable taken into account in determining optimal grape maturity for harvest. In this work, partial least square (PLS) regression models were developed to estimate TSS content for Godello, Verdejo (white), Mencía, and Tempranillo (red) grape varieties based on diffuse spectroscopy measurements. To identify the most suitable spectral range for TSS prediction, the regression models were calibrated for four datasets that included the following spectral ranges: 400–700 nm (visible), 701–1000 nm (near infrared), 1001–2500 nm (short wave infrared) and 400–2500 nm (the entire spectral range). We also tested the standard normal variate transformation technique. Leave-one-out cross-validation was implemented to evaluate the regression models, using the root mean square error (RMSE), coefficient of determination (R2), ratio of performance to deviation (RPD), and the number of factors (F) as evaluation metrics. The regression models for the red varieties were generally more accurate than the models of those for the white varieties. The best regression model was obtained for Mencía (red): R2 = 0.72, RMSE = 0.55 °Brix, RPD = 1.87, and factors n = 7. For white grapes, the best result was achieved for Godello: R2 = 0.75, RMSE = 0.98 °Brix, RPD = 1.97, and factors n = 7. The methodology used and the results obtained show that it is possible to estimate TSS content in grapes using diffuse spectroscopy and regression models that use reflectance values as predictor variables. Spectroscopy is a non-invasive and efficient technique for determining optimal grape maturity for harvest.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

Quantifying Asian chestnut gall wasp (Dryokosmus kuriphilus Yasumatsu) impact on fruit yield and on tree growth using terrestrial LiDAR

[EN] The Asian chestnut gall wasp is an invasive pest that causes ecological and economic losses in the management of the sweet chestnut (Castanea sativa Mill.). The pest therefore needs to be monitored in order to assess its impact on tree growth and fruit yield. As part of this work, we propose an infestation level classification based on the number of galls per branch. For two sweet chestnut orchards infested by the wasp, terrestrial light detection and ranging (LiDAR) data were used to calculate tree growth and fruit yield was quantified in terms of nuts and burrs. The tree growth and fruit yield variables were statistically analysed to determine the impact of different infestation levels on these variables, and differences between pairs of infestation levels were tested for significance. Negative correlations were found for the fruit yield variables with infestation indicators, while positive correlations were found for the tree growth variables. Significant differences were observed in fruit yield and tree growth variables associated with different infestation levels.SIVITICAMPO, SL (grant id: 2021/00009/001; T132).Publicación en abierto financiada por el Consorcio de Bibliotecas Universitarias de Castilla y León (BUCLE), con cargo al Programa Operativo 2014ES16RFOP009 FEDER 2014-2020 DE CASTILLA Y LEÓN, Actuación:20007-CL - Apoyo Consorcio BUCL