Projector-camera systems always need complicated geometry calibration to get a correct display result on nonplanar projection surface. Geometry registration of most calibration methods dealing with arbitrary surfaces is done by projecting a set of structure light patterns or by manually 3D modeling, which are both timeconsuming. In this paper, we propose a robust checkerboard calibration pattern recognition method to help nonplanar surface geometry registration. By approximating the nonplanar surface to be composite of many planar quad patches, pixels mapping between the calibration camera and a projector can be got by projecting only one checkerboard calibration pattern recognized by our method. Compared with geometry registration with structure light or encoded points, which need project many images, our method can be more efficient. Our recognition method has two steps: corner detection and checkerboard pattern match. Checkerboard internal corners are defined as special conjunction points of four alternating dark and bright regions. A candidate corner's neighbor points within a rectangular or a circular window are treated as in different one-point-width layers. By processing the points layers in corner detection, we transform the 2D points distribution into 1D, which simplifies the regions amount counting and also improves the robustness against noises caused by deformation and complex illumination. After corner detection, the pre-known checkerboard grids rows and columns amounts are used to match and decide the right checkerboard corners from the results that have found. Regions boundary data produced during the corner detection also assist the matching process.
High target speed, long pulse duration or wide signal bandwidth may cause noticeable scale effect on radar echoes, for which the conventional narrowband matched filter may introduce an obvious signal-to-noise ratio (SNR) loss for target detection. To obtain the ideal SNR gain in the above scenarios, a novel long-time coherent integration method has been proposed, namely wideband-scaled Radon-Fourier transform (WSRFT). The proposed WSRFT can compensate the scale effect not only on the single pulse but also among the multiple pulses in a long coherent integration time. Furthermore, the performance comparison between the proposed WSRFT and the existing Radon-Fourier transform method is given. Finally, some numerical experimental results are also provided to demonstrate the effectiveness of the proposed WSRFT method.
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