Jorge Antonio Silva Centeno

New Models for Scattering Bias Compensation in Time-of-Flight Range Camera Self-Calibration

AbstractThe geometric calibration of time-of-flight range cameras is a necessary quality assurance measure performed to estimate the interior orientation parameters. Self-calibration from a network of range imagery of an array of signalized targets arranged in one or two planes can be used for this purpose. The latter configuration requires the addition of a parametric model for internal light scattering biases in the range observations to the background plane due to the presence of the foreground plane. In a previous study of MESA Imaging SwissRanger range cameras, such a model was developed and shown to be effective. A new parametric model is proposed here because the scattering error behavior is camera model dependent. The new model was tested on two pmdtechnologies range cameras, the CamCube 3.0 and CamBoard nano, and its effectiveness was demonstrated both graphically and statistically. The improvement gained in the root-mean square of the self-calibration range residuals of 22 and 32%, respectively,...

Two Methods to Estimate the Spot Size of Terrestrial Laser Scanners

This technical note presents the results of a study focused on the evaluation of laser beam divergence and its effect on the spot size of terrestrial laser scanners. For this purpose, experiments were accomplished using the Leica HDS3000 and HDS6000 laser scanners. Two methods for the evaluation of the spot size are compared: a direct method, based on the analysis of the capacity of the laser beam to go through small slots, and an analytical method that estimates the spot diameter based on the edge effect. Based on the performed experiments, the development of a conceptual model of the edge effect at sharp edges is described for each method and validated. The experiments proved that the methods are suitable to analyze the variation of the diameter of the spot as a function of the distance. The estimate of the spot size using slots of varying sizes is a direct and easy to use method, but the computation of the spot size using the sharp edge model is more stable in relation to the point density, and can be ...

A study of integration of LIDAR and photogrammetric data sets by indirect georeferencing and in situ camera calibration

ABSTRACT This article aims to study the importance of in situ camera calibration for the integration of light detection and ranging (LIDAR) and photogrammetric data sets by indirect georeferencing. For this purpose, the in situ camera calibration was performed to estimate the interior orientation parameters (IOP) in the flight condition, using a sub-block of images (six images from two opposite flight strips), extracted from the entire block and a set of LIDAR control points (LCPs) computed by three planes intersection, extracted from the LIDAR point cloud on the building roofs. In order to evaluate the accuracies of the LIDAR and photogrammetric integration, two experiments were performed: the first used IOP from terrestrial calibration, and the second employed the IOP from the in situ calibration. The analysis of the obtained results from the performed experiments showed that the horizontal and vertical accuracies, computed by checkpoints discrepancies, are improved significantly when the IOP from in situ calibration are used. For this condition, the values of horizontal and vertical RMSEs of discrepancies are close to 0.40 and to 0.50 m, respectively.

A Study on In Situ Calibration of an Off-The-Shelf Digital Camera Integrated to a Lidar System

Photogrammetric procedures using the integration of imagery and light detection and ranging (Lidar) datasets are becoming common in mapping companies nowadays. When photogrammetric and Lidar surveys are performed simultaneously while having the camera connected to the Lidar system, the images exterior orientation parameters computed from the Lidar system can be used to perform photogrammetric applications. To implement such approach, camera calibration procedures should be applied to obtain accurate interior orientation parameters. This paper shows the performed study and experimental results from an in situ self-calibration using simultaneously collected imagery and Lidar datasets. The experimental study is conducted to devise a methodology for the in situ self-calibration that uses a set of vertical control points, extracted from Lidar point cloud, as well as the three-dimensional coordinates of the camera exposure stations, computed from the Lidar trajectory. For the small photogrammetric block used in this study, the results from the performed experiments demonstrated that the in situ self-calibration is required to obtain horizontal accuracies of approximately one image pixel on the ground in bundle adjustment assisted by direct measured of the coordinates of the camera exposure stations.

Semiautomatic extraction of main road centrelines in aerial images acquired over rural areas

In this article, a scheme for road extraction in rural areas is proposed based on a search of the road centrelines. For this purpose, the road centreline is modelled as being a chain composed of short line segments. Only small angles are allowed between adjacent segments. In order to find the next element, the Radon transform is applied. Experiments using this approach are described and the results are compared to vectors obtained by visual analysis of the image on the screen. The accuracy of the semi-automated method is evaluated considering the completeness, correctness and root mean square of extracted centrelines.

Automatic road extraction in rural areas, based on the Radon transform using digital images

Manual digitizing of road maps is an expensive and time-consuming task. We present a method based on the Radon transform, which automatically extracts roads in rural areas from digital images. The proposed method iteratively detects linear segments and then generates road centerlines. The proposed method is composed of two phases: in the first, the seed segments are detected, and in the second, road widths are measured and successive detection of line segments that are candidates as road centerlines is performed. Several tests were carried out using aerial photographs (digital images) of a rural area in Brazil, and the results are presented and discussed. The quality of the extracted road centerlines was computed using the following indexes: completeness, correctness, and RMS. The values obtained show that the proposed methodology performs well.

The use of images CBERS 2 and CBERS 2b in identification of areas affected by desertification

The process of desertification, which extends from a long time ago, became a reality in Brazil. This phenomenon can be understood as land degradation, caused by factors including climatic changes and human activities. Besides being a threat to biodiversity, causes loss of soil productivity, threatening the lives of thousands of people living in affected regions. So, the identification of affected areas is essential to diagnose and prevent the problem. Satellite image has been a source of relatively low cost and widely used in this task. Therefore, is proposed in this study, a method to extract automatically areas heavily affected by desertification. The method is based on concepts of mathematical morphology, vegetation index and classification of digital images. Experiments are conducted separately, with images of CBERS 2 and 2B, and subsequently compared. The validation is done by crossing the results obtained with a reference image, created by a manual process.

Assessing snow extent variations of Illimani mountain with Landsat NDSI

Snow in the mountains is important because it keeps freshwater resources and supplies water for agriculture and human consumption. One of the most well-known mountains in Bolivia is the Illimani. In this paper the results of a multitemporal analysis of the snow cover at the Illimani are shown. Therefore, Landsat imagery of two years, 2010, and 1016 is presented. Snow cover is estimated from Landsat imagery using image processing and a snow-index. The temporal variation along a year is also compared to historical records. The results showed the seasonal variation of the snow cover area and that the glacier area is reducing.

Augmented Reality and Maps: New Possibilities for Engaging with Geographic Data

Among the systems that aim to help users to perform map reading tasks, augmented reality (AR) is one of the most promising. However, the impact of this new technology in terms of acceptance, motivation and improvement of the learning process has still not been sufficiently explored. This study aims to assess the contribution of an AR system for map reading and for improving users’ understanding of geographic data. Landscape and census data from New Zealand were used to evaluate the performance of an AR system in an experiment involving 60 participants. Differences in the participants’ backgrounds were reflected in the way they completed the task for both printed maps and the AR system and 90% of the participants preferred to work with the AR system rather than with traditional printed maps. Users that had previous experience of the geographical dataset provided performed the task better using only the printed maps, while those without that experience performed better with the AR system.

MODELAGEM DO ERRO DEVIDO À ILUMINAÇÃO AMBIENTE NAS MEDIÇÕES OBTIDAS COM CÂMERA DE DISTÂNCIA

As câmeras de distância sao capazes de medir a distância entre o sensor e a superficie dos objetos para cada pixel da imagem, em um unico instante, produzindo uma imagem de distâncias. Alem das distâncias, tambem obtem a intensidade e a amplitude para cada pixel, formando as imagens de intensidade e amplitude, respectivamente. Como toda a medida, aquelas obtidas pelas câmeras de distância possuem erros, e um dos fatores que geram erros nas medidas e a iluminacao ambiente. Neste estudo foi analisada a influencia que a iluminacao ambiente exerce sobre os valores calculados de distância, amplitude e intensidade. Para isso, realizou-se experimentos em uma sala escura, onde foram obtidas imagens de distância, intensidade e amplitude de uma parede branca, em que incidia diversos niveis de iluminacao gerada por duas lâmpadas cujos feixes convergiam ao centro da parede. Verificou-se que: a iluminacao fornecida nos experimentos aumentou os valores de distância; a relacao entre os erros de distância e a variacao da amplitude e diretamente proporcional e linear; e que a relacao entre os erros de distância e a variacao da intensidade tambem se mostrou linear para valores de intensidade menores que 26600, para a frequencia de modulacao de 21 MHz. As correlacoes lineares atingiram valores acima de 0,9. A imagem de intensidade se mostrou mais sensivel a incidencia de iluminacao ambiente do que a imagem de amplitude.