José Herráez

High performance grid for the metric calibration of thermographic cameras

The metric calibration of thermographic cameras would make possible the acquisition of geometric data if the principles of photogrammetry are followed. Both the distortion effects introduced in the images by the lens and the perspective effect can be corrected if the calibration parameters are known. This paper presents a calibration grid that allows the automatic metric calibration of thermographic cameras. This calibration grid is made of light and easy-to-find materials to guarantee its portability and handling. The calibration parameters obtained with the presented calibration grid are verified and compared with those obtained with a temperature-based calibration grid through the evaluation of the accuracy and repeatability in the modelling of a standard artefact previously certified.

Consistency of Carbopol 971-P NF gels and influence of soluble and cross-linked PVP.

A study is made of the polymerization process of polyacrylic acid, commercially known as Carbopol 971 NF, assessing its consistency as a function of the degree of neutralization at pH values from 3 to 12, approximately. Percentage concentrations ranging from 0.1 to 1.4% (w/w) were studied. The gels obtained were non-Newtonian, and pseudoplastic. As concentration and pH rise, the consistency of the gels increase to a maximum, which appears between pH 6 and 8, allowing their use as vehicles in bioadhesive formulations for mucosal application. Over the increasing viscosity interval, functions were obtained to indicate the consistency of the gel as a function of pH and concentration. Since the correlation between the theoretical and experimental results is excellent, the equation found can be used to theoretically calculate the working concentration and pH required to secure the necessary consistency for a given vehicle. The addition of soluble polyvinylpyrrolidone (PVP), and cross-linked PVP (PVPP) does not substantially modify the rheological behavior of the gels, thus permitting their addition to usual vehicles.

Documentation for the Preservation of Traditional agro-industrial buildings in N.W. Spain using simple close range photogrammetry

Abstract Traditional agro-industrial buildings are an important part of the heritage of the Autonomous Region of Galicia (Northwest of Spain). Such heritage is nowadays in danger of disappearing. In order to preserve it, an exhaustive and rigorous work of documentation should be undertaken, as well as other actions. This paper shows the works of graphic and metric documentation undertaken by the authors with regards to a group of traditional agro-industrial buildings in Galicia. We used a method within the scope of close-range photogrammetry techniques (simple methods). The method is simple, cheap and accessible to people without specialised knowledge. The material used comprises low-cost conventional cameras, plumb lines and monoscopic digital photogrammetric stations. The accuracy of this method, assessed in comparison with topographic methods, turned out to be satisfactory for this type of buildings, for the most part of low height.

Design and calibration of a 3D modeling system by videogrammetry

Nowadays, close-range photogrammetry and a laser scanner are the two most popular techniques in reconstruction of three-dimensional objects. This paper develops a methodology based on videogrammetry to reconstruct 3D objects more quickly than conventional photogrammetric techniques and more cheaply than a laser scanner. Videogrammetry allows the capture of thousands of points in a very short space of time (like a laser scanner) and the objects geometry and texture (frames are photographic images as stereo pairs). A system composed of a video camera and a turntable support with a double platform over it has been developed. This paper shows the design, construction and calibration of the system to model 3D objects contained on the support with pinpoint accuracy.

Three-dimensional image orientation through only one rotation applied to image processing in engineering

Photogrammetry is a science with many fields of application in civil engineering where image processing is used for different purposes. In most cases, the use of multiple images simultaneously for the reconstruction of 3D scenes is commonly used. However, the use of isolated images is becoming more and more frequent, for which it is necessary to calculate the orientation of the image with respect to the object space (exterior orientation), which is usually made through three rotations through known points in the object space (Euler angles). We describe the resolution of this problem by means of a single rotation through the vanishing line of the image space and completely external to the object, to be more precise, without any contact with it. The results obtained appear to be optimal, and the procedure is simple and of great utility, since no points over the object are required, which is very useful in situations where access is difficult.

Multiple calibration bench for focal length of cameras by means of laser distance meter

The calibration of the cameras used in close-range photogrammetry is usually performed using auxiliary elements with known geometry and/or dimensions, through one or several photographs of elements with geometrical restrictions, which enable the calculation of the different parameters needed. This research suggests an improvement in these procedures through the use of one or several laser meters. The method is based on the use of calibration pillars in a laboratory, in which the cameras and laser meters subject to calibration are fixed. The cameras are calibrated by determining the relative positions of all the devices at the same time, which enables the application of the algorithm designed for hybrid laser-camera systems used for measuring in civil engineering and robotics. For this purpose, photographs and measurements are taken by laser meters over a moving object of unknown geometry and dimensions.

Three-diemensional scanner software using a video camera

This paper presents a software development for the obtaining in an automatic way of three-dimensional models of objects (e.g. sculptures, mechanical pieces). Nowadays, there is available software which is able to create three-dimensional models of objects using laser systems, but they are pretty expensive (up to 120,000 €) due to the high technology used for data capture (laser scanner). On the other hand, the software depicted in this paper develops a new process that captures the data with a simple digital video camera and a motorized pedestal (about 1200 €). This way, more than 1300 images of the object are obtained. The later analysis of the edges of all these images will completely define the geometry of the object. So, this software is able to create accurate digital models with a resolution that varies from hundreds to one million of points. In order to export these three-dimensional models the software generates VRML, or ASCII files. These models are very useful in sciences like computer graphics, architecture, mechanics, automated mapping/facilities management, etc.

Epipolar image rectification through geometric algorithms with unknown parameters

Abstract. Image processing in photogrammetry is commonly used for scene reconstruction. Although two-dimensional applications can be solved using isolated images, reconstruction of three-dimensional scenes usually requires the use of multiple images simultaneously. Epipolar image rectification is a common technique for this purpose. It typically requires internal orientation parameters and, therefore, knowledge of camera calibration and relative orientation parameters between images. A reparameterization of the fundamental matrix through a completely geometric algorithm of seven parameters that enables the epipolar image rectification of a photogrammetric stereo pair without introducing any orientation parameters and without premarking ground control points is presented. The algorithm enables the generation of different stereoscopic models with a single photogrammetric pair from unknown cameras, scanned from a book, or frames from video sequences. Stereoscopic models with no parallaxes have been obtained with a standard deviation of <0.5  pixels.

Analysis Method for Studying Groundwater under a Church

The Church of Asunción of Llíria (Valencia, Spain) is one of the best examples of the Valencian Baroque of the seventeenth century. This research is based on the study of the building from an urban, historical, and especially, a constructive view. The location of this particular church is unique because it is embedded in a mountain. First, some excavations were made into the mountain before the construction of the church started. Thus, there is a slope between the main entrance of the church and the rear. This research work provides the analysis of the ground humidity throughout the Ground Penetrating Radar (GPR) technique. We have analysed the subsoil of the whole church by various cuts or paths. Longitudinal and transversal measurements allowed us to produce a three-dimensional model of the land on which the church stands. We have also analysed the homogeneity or heterogeneity of the subsoil in each area and the presence of certain ground water routes. The rising moisture has been analysed on the walls and pillars of the church. To this end, a moisture analyser has been employed to monitor the moisture content over a period of six months. With this information, it was possible to identify points that are systematically more humid.

Stereoscopic vision through epipolarization without orientation parameters

Image epipolarization in photogrammetry is a common technique used to determine relative orientation based on collinearity and coplanarity, which usually requires scenes with multiple images. In general, these processes require internal orientation parameters, therefore the knowledge of camera calibration and relative orientation parameters between images. This paper presents a new algorithm that allows the epipolarization of a photogrammetric stereo pair without introducing any internal orientation parameter and without calculating the relative position between the images using images obtained with an unknown non-calibrated camera.