Исследование характеристик алгоритма корреляционно-экстремальной навигации для летательного аппарата

We study an experimental setup to perform pattern recognition by correlation methods. This setup implements the Pure Phase Correlation (PPC) method, let us say, it only takes into account the phase distributions of the Fourier transform of the scene and the target. An experimental study of a PPC method is presented. A phase measurement interferometric technique is used to extract the phase of the Fourier transform of the correlation function. Some aspects related to the intermodulation are examined. Experimental PPC with improved discrimination capability obtained with binary masks is also considered. The experiments are carried out with segmented scenes and with multiobject scenes.

We present a new image registration algorithm that employs Phase Correlation Method (PCM) to align rotated and translated 3D images. First, we use PCM and cylindrical coordinate transform to estimate rotation angle that aligns two images that are mutually rotated around known axis. An improvement of this technique is given to eliminate influence of noise and image differences in non-ideal conditions. Finally, an iterative optimization procedure is proposed which uses these techniques in rigid body registration tasks. We study the performance of the algorithm in simulated experiment on MRI brain image.KeywordsImage RegistrationPhase CorrelationImage Registration MethodImage Registration AlgorithmCorrelation SurfaceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Most people are not familiar with the indoor environment because most interior spaces are similar, and as such do not arouse the interest of most visitors. Although the GPS combined with the GIS has been broadly applied to many navigation applications, it might be still insufficient in an indoor environment where GPS signals are often severely obstructed. To meet the indoor requirements, the technique of RFID (Radio Frequency IDentification) was utilized to play an important locating role in the implementation of an indoor guidance system. The RFID tags, containing 1 KB capacity divided by 64 blocks, were adopted to accommodate the spatial-related information for working with the shortest routing for the system. By selecting the start and end points in the operation, the guidance system can suggest a direct, shortest distance, path. The locations of the passing points were identified and obtained by retrieving the spatial-related data from the tags next to the moving RFID reader. The guidance messages, including suggested path, modified path and moving directions, can be immediately presented to the users and arrive at their destination via the system’s graphic and voice interfaces. This guidance system has been comprehensively tested for its operation functions and was evaluated by a group of users, indicating that the average time for way finding in an indoor guidance trial can be efficiently reduced by 50%. This prototype for an indoor guidance system is expected to be capable of working on a portable device, such as a PDA or mobile phone, thereby extending its practical application.

In order to solve the problems of low accuracy of traditional Radio Frequency Identification (RFID) ranging and time overhead of frequency hopping technology that developed recently. In this paper, we propose a ranging system based on dual-band Orthogonal Frequency Division Multiplexing (OFDM) backscatter signals. First, the structure of OFDM signal is de-signed according to the characteristics of RFID communication. Then, the correlation method in time-frequency domain is used for RFID signal detection, without recovering the RFID signal. After that, the RFID channel is estimated by channel difference method. Finally, we use the Phase Difference of Arrival (PDOA) and Chinese remainder theorem to calculate the cycle ambiguity corresponding to the distance. The extensive simulation results show that the proposed method can achieve centimeter-level ranging accuracy with a single station as well as maintains a low time cost.

In this letter, an improved phase correlation (PC) method based on 2-D plane fitting and the maximum kernel density estimator (MKDE) is proposed, which combines the idea of Stone's method and robust estimator MKDE. The proposed PC method first utilizes a vector filter to minimize the noise errors of the phase angle matrix and then unwraps the filtered phase angle matrix by the use of the minimum cost network flow unwrapping algorithm. Afterward, the unwrapped phase angle matrix is robustly fitted via MKDE, and the slope coefficients of the 2-D plane indicate the subpixel shifts between images. The experiments revealed that the improved method can effectively avoid the impact of outliers on the phase angle matrix during the plane fitting and is robust to aliasing and noise. The matching accuracy can reach 1/50th of a pixel using simulated data. The real image sequence tracking experiment was also undertaken to demonstrate the effectiveness of the proposed PC method with a registration accuracy of root-mean-square error better than 0.1 pixels.

For pt.II see ibid., vol.16, no.16, p.2871 (1983). The circular orbit method (COM) which has been proposed in parts I and II is extended to coupled oscillator systems. The authors also develop a new method (they call it the phase correlation method (PCM)) which enables one to calculate a particular state manifold. They apply the COM and PCM to calculations of state energy in the Henon-Heiles and Barbanis potential systems and examine the efficiency of them.

In this paper the impact of the signal bandwidth on the performance of frequency modulated continuous wave (FMCW) radar based ranging to ultra high frequency (UHF) radio frequency identification (RFID) tags is investigated. The analyses are based on ultra-wideband (UWB) channel measurements performed in a warehouse portal, which is a severe multipath environment. It is illustrated that the available bandwidth of the usual ISM bands at 900 MHz, 2.5 GHz and 5.8 GHz is only sufficient for a precise RFID tag localization if moderate or low multipath conditions are given. However, in severe multipath channels the ISM bands are unsuited and UWB signals are needed. The results can be considered a lower bound for signal time of flight (TOF) based localization approaches that utilize Fourier or correlation methods for the signal travel time estimation.

Image-based damage assessment requires processing and analysis of two images taken at the same location and at different times. For the registration of this type of image, the traditional method based on gray information is not applicable due to the change of the image itself. Image registration based on Fourier-Mellin Transform is a global and phase correlation method which is carried on Cartesian coordinate and Log-polar coordinate. This method extracts the extreme value of the impulse function of the image phase in the frequency domain, and obtains the transformation parameters of the image. In combination with the SIFT registration method, the effect of image registration with a large rotation angle is improved. Experiments show that the algorithm is effective and feasible. Based on the registration, the difference method is used to extract the image change area. The adaptive threshold method is used to preliminarily determine the interested targets, which provides a basis for the establishment of the damage model in the next step.

The basis of the described 3D-measurement system is the method of fringe projection in combination with the principle of uniform scale representation /1 1, /2/, /3/. The measurement is characterized by the exclusive use of phase-measurement values for the coordinates of each point. To obtain the phase-measurement values the object under test is successively illuminated with a grating structure from at least three different directions with a telecentric system. A CCD-camera records the intensity distribution of the fringes intersected by the object. It should be pointed out that the values of all coordinates (x,y,z) have the same accuracies. The object to be measured and the CCD-camera are both mounted on a rotation table, turning both of them with respect to the fringe-projector about an axis. The rotation axis makes a constant angle c with the projection direction. With at least i = 3 different angle values e the linearly independent absolute phase values are obtained, which are necessary for the coordinate calculation (applying gray-code in conjunction with four 90 degs phase-shifts). In our setup we can choose up to I = 1 5 rotation angles, so that awkward areas of the surface, like zones with either specular reflection or shadows, are shifted over the surface and have nearly no influence on the results of measurements. So, we obtain the 3D-coordinates of a single patch of the object. We have expanded the system to include a second rotation axis, where the object can rotate within the measurement volume. The CCD-camera will then get different views of the object. The second rotation axis is tilted against the first axis by an angle S. Depending on the class of objects there are different possible tilt-angles S. Typically we choose ö = 300. By rotating the object around the first axis with a rotation angle -y (j = number of patches) it is possible to measure the object from different viewpoints, whereby for each patch or viewpoint the procedure described above is used. For a convenient handling of the data-set the restriction j 8 is used. The actual rotation angles e and y were measured with angle encoders. The free geometric parameters (grating periode A and projection angle a) and the orientation in space of the second axis are gauged before the measurement procedure as described below. By measuring a number of patches we have the problem of transforming them from a local coordinate system into a global one. The combination of the different patches into one coordinate system without interactive user help was solved by developing a calibration method for the second axis. In combination with an absolute phase measurement all patches were measured in a known space orientation, so that we obtain the 3D-picture by rotation of each patch around the second axis. Correlation methods or special points are not necessary. To obtain the 3Dorientation of the second axis one can use a calibration procedure with a special calibration body whose 3Dcoordinates are measured for different rotation positions whereby the second axis has to cross the plane near the centre.

In this paper, signal processing techniques are employed for electromagnetic sub-wavelength imaging. Three signal processing algorithms are investigated, including phase conjugation (PC), correlation method (CM) and maximum search and removal method (MSRM).

The work considers the artifacts compensation in the context of airborne ultrasonic image generation. Almost all airborne ultrasonic images used in robotics have artifacts and distortions, when comparing the real objects to those presented or identified in ultrasonic images. The differences between the real and reference images can have various causes, such as asymmetries in the directivity of the ultrasonic transducers, reflections in the explored environment, and nonlinearities of the signal processing blocks. A fusion-based method of reducing artifacts of sonar images is proposed and partially implemented. The object image from the ultrasonic image is fused with a reference image, selected from a database after an identification procedure. The selection rule used in image fusion is considered a supervised process. The results are encouraging and suggest a trade-off between complexity of fusion technique and quality of the result.

A class of implementations of mutual information (MI) based image registration estimate MI from the joint histogram of the overlap of two images. The consequence of this approach is that the MI estimate thus obtained is not overlap invariant: its value tends to increase when the overlapped region is getting smaller. When the two images are very noisy or are so different that the correct MI peak is very weak, it may lead to incorrect registration results using the maximization of mutual information (MMI) criterion. In this paper, we present a new joint histogram estimation scheme for overlap invariant MI estimation. The idea is to keep it a constant the number of samples used for joint histogram estimation. When one image is completely within another, this condition is automatically satisfied. When one image (floating image) partially overlaps another image (reference image) after applying a certain geometric transformation, it is possible that, for a pixel from the floating image, there is no corresponding point in the reference image. In this case, we generate its corresponding point by assuming that its value is a random variable following the distribution of the reference image. In this way, the number of samples utilized for joint histogram estimation is always the same as that of the floating image. The efficacy of this joint histogram estimation scheme is demonstrated by using several pairs of remote sensing images. Our results show that the proposed method is able to produce a mutual information measure that is less sensitive to the size of overlap and the peak found is more reliable for image registration.

The objective of this paper is to develop a vision-based navigation technique for micro aerial vehicles, quadrotor type, to operate in GPS-denied environment. The navigation method has been developed while using appearance-based Visual-Teach-and-Repeat (VT&R) technique. In a teaching phase, a quadrotor is manually navigated along a desired route to collect a set of reference images. In a repeating phase, the quadrotor is able to autonomously follow the desired route using these reference images. Self-localization is developed to determine the current segment of the desired route by a number of Speeded-Up Robust Features (SURF), matched between the current image and the reference images. In this paper, three methods of self-localization are proposed and compared. After performing self-localization, the quadrotor computes appearance-based motion control commands (desired yaw and height) for the next movement in order to keep track of the desired route. This computation is developed on Funnel Lane theory, which was originally proposed in Chen and Birchfield (IEEE Trans. Robot. 25(3), 749---754 (11)) for 2D navigation of a ground vehicle. The paper extends this theory to 3D navigation of a quadrotor.The proposed self-localization methods are tested with several image databases. Finally, an online experiment of proposed VT&R technique is demonstrated using Ar.Drone quadrotor model.

Over the last number of decades, tall building geometries have been shifting from rectangular boxes towards shapes that are defined through geometrical transformations such as twisting. While, from an aesthetical point of view, these twisting geometries make tall buildings appear contemporary and iconic, from an environmental point of view, however, the benefits are not as straightforward. They may vary significantly based on climatic loads and urban conditions, among others. This study aims to assess the self-shading benefits of twisting geometries by finding a correlation between floor-to-floor rotation and facade solar irradiation across climates, primarily focusing on hot ones, where self-shading is used as a passive solar design strategy. The study analysed three types of irradiation studies: Cumulative Annual Irradiation, Cumulative Harmful Irradiation during Cooling Design Day, and lastly, Solar Irradiation Self-Shading Balance. The latter compares beneficial and harmful solar irradiation during Hot and Cold Degree Days to quantify the impact of floor-to-floor rotation on optical and thermal performance. The study explored hundreds of possible scenarios across different climates and various floor-to-floor rotation angles, revealing a variety of positive, negative, and neutral situations. The study recommends careful examination of environmental conditions via a combination of multiple irradiation studies, particularly in the case of a smooth facade scenario.

This work presents the designs of single-layer chipless radio frequency identification (RFID) tags based on the RF-encoding particles (REP) approach. These tags are the first realized for reading in cross-polarization resulting in a higher immunity against multipath, and thus, achieving robust readings in a practical environment. The proposed chipless tags are of credit-card size, with a frequency band of operation ranging from 3 to 6 GHz within the ultra-wideband (UWB), compliant with low-cost additive fabrication techniques, and realized with low-cost plastic and paper substrates. A study on reader-tag polarization and rotation angle is performed for the proposed designs and compared with the existing designs of two-layers. For the first time, it is presented that the low-cost single-layer tags can be read in realistic environments with only one measurement.