Jaime Riera

Measuring coupled oscillations using an automated video analysis technique based on image recognition

The applications of the digital video image to the investigation of physical phenomena have increased enormously in recent years. The advances in computer technology and image recognition techniques allow the analysis of more complex problems. In this work, we study the movement of a damped coupled oscillation system. The motion is considered as a linear combination of two normal modes, i.e. the symmetric and antisymmetric modes. The image of the experiment is recorded with a video camera and analysed by means of software developed in our laboratory. The results show a very good agreement with the theory.

Contribution of digital simulation in visualizing physics processes

In our experience of teaching physics for engineering at university level we have learned that the mathematical relationships between the parameters that control a process are important, but not sufficient, to understand a process. Such knowledge will only be consolidated if the new concept is incorporated by student in his field of study. Simulation programs, especially through visualization, can help to attain this target. We have developed three programs using Visual Basic. One of them is devoted to fitting experimental data and is complementary to experimental work; the others focus on dynamics, translation, and rotational movement, helping to understand the Newtons laws.

Handling occlusion in object tracking in stereoscopic video sequences

In this paper, we study simple algorithms for three-dimensional tracking objects in a stereo video sequence, by combining optical flow and stereo vision. This method is not able to handle the occlusion of the moving objects when they disappear due to an obstacle. To improve the performance of this method, we propose the use of adaptive filters and neural networks to predict the expected instantaneous velocities of the objects. In the previous works, this system has been successfully proved in two-dimensional tracking.

Using image recognition to automate video analysis of physical processes

Multimedia technologies and video analysis allow the design of low-cost physical measurement and data acquisition systems. The number of pixels in the images limits their spatial resolution, whereas their time resolution depends on the number of frames recorded per second. Both characteristics are determined by the video recording system used. We have developed a laboratory system with these characteristics where important improvements have been reached by using image recognition to automate video analysis. In the present work we first examine several image recognition techniques and evaluate them from the point of view of their application to measurement systems. Then we describe the proposed system and the methodology followed in the measurement process. An image of an experimental object is recorded and used as a filter, while the sequence of images of that object in motion become the input frames for the recognition process. Finally, we discuss the results obtained by this measurement process and comp...

Handling occlusion in optical flow algorithms for object tracking

In this paper, we study simple algorithms for tracking objects in a video sequence, based on the selection of landmark points representative of the moving objects in the first frame of the sequence to be analyzed. The movement of these points is estimated using a sparse optical-flow method. Methods of this kind are fast, but they are not very robust. Particularly, they are not able to handle the occlusion of the moving objects in the video. To improve the performance of optical flow-based methods, we propose the use of adaptive filters and neural networks to predict the expected instantaneous velocities of the objects, using the predicted velocities as indicators of the performance of the tracking algorithm. The efficiency of these strategies in handling occlusion problems are tested with a set of synthetic and real video sequences.

Object tracking with a stereoscopic camera: exploring the three-dimensional space

The experimental analysis of three-dimensional (3D) movement is of great importance to introduce students to knowledge of the actual physical world. However, the difficulties of collecting 3D data make it little suitable for beginner physics students. In this work, we propose an experiment to analyse 3D motion in stationary and rotating systems. A projectile is launched from a rotating platform. The tracking of the projectile is carried out with the assistance of a stereoscopic camera and simplified object tracking techniques. The experiment can be modelled through the well-known transformation equations between an inertial reference system and a non-inertial one with constant angular velocity. The simplicity of the method and the agreement between the experimental data and the theoretical model make the experiment accessible to undergraduate physics students. In this way, they can easily measure a 3D movement and verify its theoretical equations.

Digital simulation of wave motion

Information and communication technologies have been shown to be very effective in the transmission of scientific knowledge. Nowadays, the development of software and hardware makes it possible to simulate processes as close to reality as we want. However, when we are trying to explain some complex physical processes, it is better to simplify the problem by means of simplified pictures of the total process. In the present work, we analyze the design of a simulation program of wave motion developed in our laboratory. The aim of the program is to help students to understand the basic concepts of the wave motion. For this reason, we have paid special attention to interactivity and graphic aspects.

Testing Theoretical Models of Magnetic Damping Using an Air Track.

Magnetic braking is a long-established application of Lenzs law. A rigorous analysis of the laws governing this problem involves solving Maxwells equations in a time-dependent situation. Approximate models have been developed to describe different experimental results related to this phenomenon. In this paper we present a new method for the analysis of magnetic braking using a magnet fixed to the glider of an air track. The forces acting on the glider, a result of the eddy currents, can be easily observed and measured. As a consequence of the air track inclination, the glider accelerates at the beginning, although it asymptotically tends towards a uniform rectilinear movement characterized by a terminal speed. This speed depends on the interaction between the magnetic field and the conductivity properties of the air track. Compared with previous related approaches, in our experimental setup the magnet fixed to the glider produces a magnetic braking force which acts continuously, rather than over a short period of time. The experimental results satisfactorily concur with the theoretical models adapted to this configuration.

Fuzzy control for obstacle detection in object tracking

In previous works, we have studied a fast and robust object tracking system based on optical flow. To solve the occlusion problem, we have developed a combined tracking system based on optical flow and adaptive filters. The critical point of the system is the coupling between optical flow and predictive algorithms. This coupling is governed by parameters such as tolerance, the absolute value of the difference between the value of velocity calculated by the optical flow and the estimated value. In this paper, we propose the use of a fuzzy control system to solve this coupling problem between the different velocities. This technique will provide great robustness to the tracking algorithm.

Experimental analysis of nonlinear oscillations in the undergraduate physics laboratory

In this paper, we present a simple experiment to introduce the nonlinear behaviour of oscillating systems in the undergraduate physics laboratory. The transverse oscillations of a spring allow reproduction of three totally different scenarios: linear oscillations, nonlinear oscillations reducible to linear for small displacements, and intrinsically nonlinear oscillations. The chosen approach consists of measuring the displacements using video photogrammetry and computing the velocities and the accelerations by means of a numerical differentiation algorithm. In this way, one can directly check the differential equation of the motion without having to integrate it, or perform an experimental study of the potential energy in each of the analysed scenarios. This experiment allows first year students to reflect on the consequences and the limits of the linearity assumption for small displacements that is so often made in technical studies.