Lubos Rejfek

Navigation of robotics platform using monocular visual odometry

Precise navigation of mobile robots in unknown areas is common problematic in many research papers. For navigation in outdoor areas Global Navigation Satellite System (GNSS) is typically used. For better position estimation in Europe augmentation satellite system called European Geostationary Navigation Overlay Service (EGNOS) it is used. In US it is similar system called Wide Area Augmentation System (WAAS). These systems are not usable in indoor areas because the weak of signal and the low position accuracy. For indoor areas, it is necessary to use an alternative navigation system - independent on satellite navigation. In our research we are focusing on visual odometry using a monocular camera. Advanced image processing methods on camera images to achieved accurate visual odometry are applied.

Correction of radar received signal

This paper shown the correction of the radar power in dependence on the target distance. This correction is important for right type estimation of the target. Type of the used radar is frequency modulated interrupted continuous wave radar. This radar receives different length of the pulse for the different distances of the targets and different transmitted pulses. Received powers are analyzed by the power spectral density methods. The Fourier transform is used in this paper. Results from this work are important for the radar reflectivity measurement and these results will be implemented to the real radar system.

System for Automatic Detection and Analysis of Targets in FMICW Radar Signal

Abstract This paper presents the automatic system for the processing of the signals from the frequency modulated interrupted continuous wave (FMICW) radar and describes methods for the primary signal processing. Further, we present methods for the detection of the targets in strong noise. These methods are tested both on the real and simulated signals. The real signals were measured using the developed at the IAP CAS experimental prototype of FMICW radar with operational frequency 35.4 GHz. The measurement campaign took place at the TU Delft, the Netherlands. The obtained results were used for development of the system for the automatic detection and analysis of the targets measured by the FMICW radar.

Comparison of parametric methods for radar signal processing

The paper deals with comparison of parametric power spectral density methods for the utilization in the meteorological radar. Type of the considered radar is pulse radar of frequency modulated pulses. We have compared duration of signal processing requested by single methods involved in the test. The methods used are the Auto Regressive (AR) model, MUSIC method, Eigen Vector algorithm and CAPON. Duration of signal processing is important for regular measurements of the radar. The best results we obtained for the AR model.

Attenuation of optical signal in free space - Event analysis

Institute of Atmospheric Physics ASCR operates a dual-wavelength free space optical (FSO) link at meteorological observatory Milesovka (837 m.a.s.l.). Relevant meteorological quantities which attenuate the signal are also measured. To understand the physics behind also individual attenuation events are to be analyzed. This contribution focuses on interesting events with fog, rain and other meteorological phenomena which cause a high attenuation or an outage. Comparisons with theoretical models are also discussed. Widely known models describe signal behavior in individual situations, when only one type of meteorological phenomenon occurs. This paper shows an effect of different attenuation phenomena combinations.

Improving precision of laser line detection in 3D range scanning systems

Nowadays lasers in the measurement industry are widely used. The accuracy of optical rangefinders, which detect a laser line directly from a taken frame, lies in precise laser line detection. Unfortunately, during the measurement process some laser line reflections can occur, laser colored objects are present on the scene or segmented laser line is too wide due to the laser saturation effect. These mentioned phenomena have influence on the measurement precision. It is possible to suppress these effects partially by checking the laser line width, but these points are missing in final measurement results. This paper describes a detailed analysis of segmented laser line components for elimination these phenomena, and the final distinguishing, which parts of a segmented laser line are used in measurement process. The paper also includes a comparison with a centroid method, which was used for a laser line center estimation.

Effective lens distortion correction for 3D range scannig systems

Nowadays lasers in the measurement industry are widely used. The accuracy of optical rangefinders, which detect a laser line directly from a taken frame, lies in precise laser line detection. By using a lens with a smaller focal length, a barrel distortion can occur. In this paper we would like to introduce an effective method for barrel distortion correction. The algorithm also includes a super-sampling method to prevent line discontinuities especially on image borders, where the influence of distortion effect is significant. The algorithm description also includes substantial speed-up of the whole process by using a correction matrix. A correction matrix is estimated only once for a specific frame dimension and users parameters. Then the camera correction matrix is used in the mapping process. The paper also includes a time comparison between using a different super-sampling quality and the benefit of using the correction matrix.

Correction of received power for Doppler measurements by FMICW radars

This electronic document is aimed at the corrections of the received power through frequency modulated interrupted continuous wave radars. These corrections are important for the correct interpretation of the target characteristics. Power corrections, described in this paper, are modified for the measurement of the Doppler shifts. Doppler shifts are calculated by the using of the two dimensional fast Fourier transform. In practical part of this paper four types of windows were compared during calculation of the two dimensional spectra. We concluded that the correction coefficients should be determined for each window individually.

Sensitivity analysis of PCDR35 radar

This conference paper is aimed at the analysis of the frequency modulated interrupted continuous wave radar (PCDR35). This radar was developed under the Institute of Atmospheric Physic Czech Academy of Sciences leadership. A primary aim of this radar is the monitoring of meteorological targets (rain cells, hail stones and other). In this paper a radar measurement of the corner reflector with the theoretical reflectivity determination are compared. In the last part of this paper an evaluation of this radar and possible modifications (classical FMCW) are described.

The point cloud visualisation for rotary optical rangefinders

This paper describes the point cloud visualization for rotary optical rangefinders. Measured distance data with image information from captured frames give a possibility to create a colored point cloud. The distance is measured by the vertical laser line and to select a color value directly from an actual measured frame is not possible. For this reason, the previous measurement frame is used. The individual frames shifting is estimated by the temple matching algorithm. The purpose of the paper is to show how easily it is possible to combine measurement data with image information in case of a color point cloud construction. The paper includes several examples of different point clouds to verify the algorithms ability.