José Alexandre de França

A new robust algorithmic for multi-camera calibration with a 1D object under general motions without prior knowledge of any camera intrinsic parameter

In computer vision, camera calibration is a necessary process when the retrieval of information such as angles and distances is required. This paper addresses the multi-camera calibration problem with a single dimension calibration pattern under general motions. Currently, the known algorithms for solving this problem are based on the estimation of vanishing points. However, this estimate is very susceptible to noise, making the methods unsuitable for practical applications. Instead, this paper presents a new calibration algorithm, where the cameras are divided into binocular sets. The fundamental matrix of each binocular set is then estimated, allowing to perform a projective calibration of each camera. Then, the calibration is updated for the Euclidean space, ending the process. The calibration is possible without imposing any restrictions on the movement of the pattern and without any prior information about the cameras or motion. Experiments on synthetic and real images validate the new method and show that its accuracy makes it suitable also for practical applications.

Revisiting Zhang's 1D calibration algorithm

In recent years, the camera calibration using 1D patterns has been studied and improved by researchers all over the world. However, the progress in that area has been mainly in the sense of reducing the restrictions to the 1D pattern movement. On the other hand, the methods accuracy still demands improvements. In the present paper, the original technique proposed by Zhang is revisited and we demonstrate that the methods accuracy can be significantly improved, simply by analyzing and reformulating the problem. The numerical conditioning can be improved if a simple data normalization is performed. Furthermore, a non-linear solution based on the Partitioned Levenberg-Marquardt algorithm is proposed. That solution takes advantage of the problems particular structure to reduce the computational complexity of the original method and to improve the accuracy. Tests using both synthetic and real images demonstrate that the calibration method using 1D patterns can be applied in practice, with accuracy comparable to other already traditional methods.

Fringing Field Capacitive Sensor for Measuring Soil Water Content: Design, Manufacture, and Testing

Capacitors are used as sensors in several applications. Typically, the quantity to be measured changes either the geometric properties of the structure used as a capacitive sensor or the physical properties of the dielectric between the electrodes of that structure. On the other hand, if the sensor geometry maximizes the capacitance due to fringing, then the possibilities are totally different. In this case, the electric field can be projected onto the test sample. This paper covers the usage of fringing field sensors to measure the water present in the soil. We examine how the geometry of the PCB-made interdigited electrode structure influences the characteristics of the sensor. However, fringing field sensors are difficult to be analytically modeled due to its intrinsic nonlinear characteristic. Therefore, our conclusions were mainly based on results of simulations, but we also tried to reproduce the results of the simulations experimentally. Also, we discuss a circuit that converts the changes in the sensors capacitance into variations in the width of a pulse signal. Finally, the proposed solution has been experimentally compared with the standard gravimetric method to quantify the water content in the soil. The results were encouraging since the proposed sensors measurements fit to the experimental data with a coefficient of determination R2= 0.94.

A Low-Cost NIR Digital Photometer Based on InGaAs Sensors for the Detection of Milk Adulterations With Water

The adulteration of milk with water is a very common problem, which reduces its nutritional value and industrial yield, and can also represent a major risk of contamination. The standard method for detecting this kind of fraud is the cryoscopy, which fails when the adulteration is done along with other substances. Therefore, there is a need for new and more robust techniques for this purpose. With this goal, we propose a prototype of a digital photometer to quantify water added to milk. This is a microcontrolled, portable device, which uses three LEDs with emission in the near-infrared (IR) region and was developed without the use of lenses, filters, or moving parts. This equipment measures the transmittance of IR radiation through milk samples to assess the addition of water. In this paper, we present the results of experiments that were conducted with diluted milk samples containing 0%-25% of added water, using the proposed equipment and the standard method of cryoscopy. In the measurements of the percentage of added water, the mean absolute error was <;1%. In terms of repeatability, in two sets of ten measurements, we obtained absolute deviations from the average corresponding to less than 0.7% of added water. Results show that the prototype response is similar to the one of a commercial cryoscope but faster.

Development of a Hardware Platform for Detection of Milk Adulteration Based on Near-Infrared Diffuse Reflection

Generally, detection of water adulteration in milk is performed using a cryoscope. However, the equipment may present erroneous results when other adulterants, e.g., urea, are added to milk. One of the techniques capable of overcoming situations in which the cryoscope fails to detect fraud is near-infrared (NIR) spectroscopy. Unfortunately, the development of an instrument based on this technology is challenging due to the influence of external factors and low signal-to-noise ratio. This paper presents a hardware platform based on NIR diffuse reflectance spectroscopy. It can be used to determine the concentration of substances in solid and liquid samples that present diffuse reflectance. An optical condenser system was developed using fixed lenses to increase the signal-to-noise ratio. LEDs with specific spectral emission were used as the light source. In addition, InGaAsSb sensors, which present rapid response and good sensitivity to the NIR spectrum, were used to detect diffusely reflected light. The proposed instrument was tested on milk samples adulterated with water. The results presented high coefficients of determination, higher than 0.99. Therefore, the developed system may be used for detection of milk adulteration. For this purpose, the system response for other variables as milk composition and addition of adulterants other than water must be studied.

Dynamics design and simulation for mobile robots navigation systems

This paper presents the virtual environment implementation for project simulation and conception of supervision and control systems for mobile robots, that are capable to operate and adapting in different environments and conditions. This virtual system has as purpose to facilitate the development of embedded architecture systems, emphasizing the implementation of tools that allow the simulation of the kinematic conditions, dynamic and control, with real time monitoring of all important system points. For this, an open control architecture is proposal, integrating the two main techniques of robotic control implementation in the hardware level: systems microprocessors and reconfigurable hardware devices. The implemented simulator system is composed of a trajectory generating module, a kinematic and dynamic simulator module and of a analysis module of results and errors. All the kinematic and dynamic results shown during the simulation can be evaluated and visualized in graphs and tables formats, in the results analysis module, allowing an improvement in the system, minimizing the errors with the necessary adjustments optimization. For controller implementation in the embedded system, it uses the rapid prototyping, that is the technology that allows, in set with the virtual simulation environment, the development of a controller project for mobile robots. The validation and tests had been accomplish with nonholonomics mobile robots models with differential transmission.

Development of 3-D Ultrasonic Anemometer With Nonorthogonal Geometry for the Determination of High-Intensity Winds

The wind speed is an important quantity in various areas of knowledge. Among the existing types of anemometers, the ultrasonic is the one that requires less maintenance and may be used in most applications. This paper presents the development of an ultrasonic anemometer that measures wind speed in three dimensions. It discusses the important aspects of the mechanical structure of the equipment in order to minimize its influence in measurements. It also presents the electronic circuits used in the excitement and in the conditioning of signals of the transducers that make up the instrument. The equipment was calibrated in a wind tunnel, with a coefficient of determination

Nonlinear Estimation of the Fundamental Matrix with Only Five Unknowns

{R^{2}}=0.999994

Calibração binocular com gabaritos 1D sem restrição demovimentos

, in relation to the reference method. In addition, results of field tests comparing two different mechanical structures are presented. Empirically, it is shown that a nonorthogonal arrangement for the anemometer favors the accuracy of the measurements. The results showed that the proposed equipment has an excellent accuracy for the measurement of up to 160 km/h.

Topology of a Network for Wireless Transmission of Data for Use in Precision Agriculture

Two images captured by an uncalibrated binocular vision system are related by the epipolar geometry. This geometry is completely characterized by a 3 x 3 matrix, called the fundamental matrix, which can be obtained from a set of point correspondences. This paper presents a new nonlinear method to calculate the fundamental matrix. To impose the rank two restriction, the method uses a quite simple parametrization. It has the advantage of having a reduced search space, with only five unknowns. Experimental tests demonstrated that the new method obtain accurate results for a large set of point correspondences. In this case, the quality of the estimated matrix is as good as the obtained with other nonlinear methods. However, the results are obtained at a low computational cost and with rapid convergence.