城市设计中视线分析的控制方法与应用研究

视线分析方法已成为目前国内城市规划设计中对建筑高度等进行控制的重要依据,其主要的技术方法主要有视廊和视面两种,本文归纳阐述了视线控制的原理、方法及不同情况下的应用。

空间交会停靠的视线控制方法

空间交会停靠控制方法经常采用的一种是基于视线位置信息的平行接近法。在ρ-ρ相平面内，定义开关线为S=ρ^2-λ^2ρ，也可以称为滑动模态，采用发动机开关控制为：u=-Fsgn(S)，研究了这种控制方法后，发现在开关线上，系统不是渐进稳定的。本文在研究了这种控制方法后，对滑动模态的表达式进行了改进，增加了阻尼项，改进后的滑动模态为：S=ρ^2+k1ρ+k2ρ,k1、k2的符号待定，并对改进后的滑动模态控制进行了稳定性证明，证明了系统在滑动模态上也是渐进稳定的。

基于改进自适应积分视线制导方法的欠驱动无人水面艇路径跟踪控制

为提高无人水面艇(unmanned surface vehicle,USV)对复杂海况的适应性,针对欠驱动USV的路径跟踪控制问题,设计基于改进的自适应积分视线(improved adaptive integral line-of-sight,IAILOS)制导方法和径向基神经网络(radial basis function neural network,RBFNN)的积分滑模路径跟踪控制器。在IAILOS制导方法中,引入降阶的扩张状态观测器估计未知时变洋流速度,从而使得该制导方法不仅可以估计时变漂角,而且可以补偿未知时变洋流的扰动。利用RBFNN的无限逼近特性来估计USV动力学模型中的不确定项和未知的外部环境干扰。通过稳定性分析和仿真对比实验,验证了本文所设计的控制器的准确性和鲁棒性。

基于视线的地形可视性分析研究

地形可视性分析在军事、电信、旅游等领域有着广泛的应用。各种复杂的、和应用有关的可视性分析大多数采用的是基于视线(LineofSight,LOS)的方法。文章在阐述视线方法的基础上,根据分析对象的不同对地形可视性分析问题进行了分类,并且从数学模型和实验仿真两方面对各种类型的可视性分析的联系和区别进行了研究,在此基础上提出了关于地形可视性分析的统一模型以及对可视性问题解决方法的一些展望。

用全站仪进行三、四等水准测量的方法设计

全站仪测角瞄准与测距接收光路同轴、机座与机身可分离、仪器横轴与棱镜同高等特性设计,为用全站仪进行三、四等水准测量时进一步延长视线长度提供了可能。本文讨论并提出了四等水准视线长度可达2000m;三等水准视线长度可达700m的观测方法。

Noise Reduction of Welding Defect Image Based on NSCT and Anisotropic Diffusion

In order to reduce noise effectively in the welding defect image and preserve the minutiae information, a noise reduction method of welding defect image based on nonsubsampled contourlet transform(NSCT) and anisotropic diffusion is proposed. Firstly, an X-ray welding defect image is decomposed by NSCT. Then total variation(TV) model and Catte_PM model are used for the obtained low-pass component and band-pass components, respectively. Finally, the denoised image is synthesized by inverse NSCT. Experimental results show that, compared with the hybrid method of wavelet threshold shrinkage with TV diffusion, the method combining NSCT with P_Laplace diffusion, and the method combining contourlet with TV model and adaptive contrast diffusion, the proposed method has a great improvement in the aspects of subjective visual effect, peak signal-to-noise ratio(PSNR) and mean-square error(MSE). Noise is suppressed more effectively and the minutiae information is preserved better in the image.

A simple rectification method for linear multi-baseline stereovision system

The linear multi-baseline stereo system introduced by the CMU-RI group has been proven to be a very effective and robust stereovision system. However, most traditional stereo rectification algorithms are all designed for binocular stereovision system, and so, cannot be applied to a linear multi-baseline system. This paper presents a simple and intuitional method that can simultaneously rectify all the cameras in a linear multi-baseline system. Instead of using the general 8-parameter homography transform, a two-step virtual rotation method is applied for rectification, which results in a more specific transform that has only 3 parameters, and more stability. Experimental results for real stereo images showed the presented method is efficient.

A Study on Dynamic Response of Cable-Seabed Interaction

A numerical method is developed to investigate the dynamic response of cable-seabed interaction in this paper. The motion of cable is described by the Lumped Parameter Method, while the seabed, unlike the prevailing simplified model of elastic foundation, is modeled as an irregular continuous rigid surface with rebound and friction existing, and the forces exerted by the seabed consist of normal counterforce and isotropic tangential Coulomb friction resistance. To describe the detailed dynamic response, two coefficients are introduced by analogy with the theory of rigid body collision with friction. The cable-seabed kinematic and dynamic contact conditions are formulated subsequently, and are used to incorporate the seabed effect into the cable dynamics to produce a set of ordinary differential governing equations. In this paper, we employ 4th order Runge-Kutta method to solve these equations. Several simulation cases are presented to illustrate the seabed effect. The results show that friction and impact have a prominent influence on the statics and dynamics of the cable.

A network-aware error-resilient method using prioritized intra refresh for wireless video communications

We propose a novel prioritized intra refresh method for the wireless video communication.The proposed method considers the characteristics of the human visual system,the error-sensitivity of the bitstream,and the state of the time-varying wireless channel jointly.An expected perceptual distortion model was used to adjust the intra refresh rate adaptively.This model consists of the perceptual weight map based on an attention model,the bit error probability map based on bitstream size,and the dynamic channel state information(CSI).Experimental results indicate that,compared with other intra refresh methods that consider only the content of the video or the CSI,the proposed method improves the average peak signal-to-noise ratio(PSNR) of the whole frame by about 0.5 dB,and improves the average PSNR of the attention-area by about 0.8 dB.

Dispersion relation and surface gravity of universal horizons

In Einstein-aether theory,violating Lorentz invariance permits some super-luminal communications,and the universal horizon can trap excitations traveling at arbitrarily high velocities.To better understand the nature of these universal horizons,we first modify the ray tracing method,and then use it to study their surface gravity in charged Einstein-aether black hole spacetime.Instead of the previous result by Cropp et al.,our results show that the surface gravity of the universal horizon is dependent on the specific dispersion relation,k_(uh)-2(z-1)k_(uh)/z,where z denotes the power of the leading term in the superluminal dispersion relation,characterizing different species of particles.And the associated Hawking temperatures also are different with z.These findings,which coincide with those derived by the tunneling method,provide some full understanding of black hole thermodynamics in Lorentz-violating theories.