薄透镜成象快速调节技术

本文结合象差理论,分析了薄透镜成象的几个先路图,介绍了相应的快速调节技术．     

Feature sequencing in the rapid design system using a genetic algorithm

This paper addresses the feature sequencing problem in the Rapid Design System (RDS). The RDS is a feature-based design system that integrates product design and process planning. An important issue in feature-based process planning for machined parts is the order in which material is removed to form the resultant part. The order, or sequence, is partially dependent on the geometric relationships between features. The sequence affects the safety, the time it takes to machine the part, and the quality of the finished part. The sequence of material removal depends on two types of relations between features: (1) intersections and (2) interfeature associations. Both types of relations compound the search for an optimal sequence of material removal. Therefore, the research problem has been the discovery and development of a genetic algorithm (GA) that efficiently searches the solution space for all possible sequences and identifies the best sequences in terms of safety, time and quality.     

Transformation of a thin-walled solid model into a surface model via solid deflation

A simplified geometric model with lower dimensionality, such as a mid-surface model, is often preferred over a detailed solid model for the analysis process, if the analysis results are not seriously impacted. In order to derive a mid-surface model from a thin-walled solid model, in this paper, we propose a novel approach called the solid deflation method. In this method, a solid model is assumed to be created by using air to inflate a shell that comprises the surface of the solid model. First, the model is simplified by the removal of any detailed features whose absence would not alter its overall shape. Next, the solid model itself can be converted into a degenerate solid model with zero thickness. Finally, a surface model is generated by splitting large faces paired in the thinned solid model, selecting one face per pair for creating a sheet model, and sewing the selected faces. Using this method, a more practical and usable mid-surface model can be very efficiently generated from a solid model because it can circumvent not only the tedious trimming and extension processes of the medial axis transformation method but also the time-consuming patch joining process of the mid-surface abstraction approach.     

光纤陀螺输入轴失准角温度补偿研究

提高温度特性是光纤陀螺仪工程化的一个难题,温度补偿是解决该问题的一种有效方法。光纤陀螺与温度相关误差项主要为零漂和标度因数,输入轴失准角也是影响光纤陀螺应用的一个重要误差项。在大量试验的基础上,分析了光纤陀螺输入轴失准角误差产生机理,采用多项式拟合方法建立了输入轴失准角误差全温模型,对多套光纤陀螺进行了全温补偿。试验结果表明,输入轴失准角补偿前全温变化在2?10^-3rad数量级,补偿后全温变化小于3?10^-4rad,精度提高了近一个数量级,大大提高了光纤陀螺仪的全温性能。     

基于被动声纳浮标投放法的水下目标跟踪

针对航空反潜中使用空投被动声纳浮标对潜艇进行跟踪的问题,利用双曲线交汇法定位,研究被动浮标对水下目标进行连续跟踪的方法,建立相应数学模型。仿真结果证明了该方法的可行性,得到目标的航速、航向、运动状态变化间隔、声纳浮标位置等因素变化与跟踪所需声纳浮标数量的关系。     

球面上的K最近邻查询算法

针对球面上数据对象点集的特征和K最近邻查询的需求,提出2种处理球面上K最近邻查询的算法:基于查询轴的K最近邻查询算法(PAM方法)和基于查询圆面的K最近邻查询算法(PCM方法).对2种算法进行实验比较,结果表明,PAM方法和PCM方法都适合处理球面上的最近邻查询问题,PAM方法在存储量和查询复杂度方面相对于PCM方法具...     

Distance functions and skeletal representations of rigid and non-rigid planar shapes

Shape skeletons are fundamental concepts for describing the shape of geometric objects, and have found a variety of applications in a number of areas where geometry plays an important role. Two types of skeletons commonly used in geometric computations are the straight skeleton of a (linear) polygon, and the medial axis of a bounded set of points in the k-dimensional Euclidean space. However, exact computation of these skeletons of even fairly simple planar shapes remains an open problem.In this paper we propose a novel approach to construct exact or approximate (continuous) distance functions and the associated skeletal representations (a skeleton and the corresponding radius function) for solid 2D semi-analytic sets that can be either rigid or undergoing topological deformations. Our approach relies on computing constructive representations of shapes with R-functions that operate on real-valued halfspaces as logic operations. We use our approximate distance functions to define a new type of skeleton, i.e, the C-skeleton, which is piecewise linear for polygonal domains, generalizes naturally to planar and spatial domains with curved boundaries, and has attractive properties. We also show that the exact distance functions allow us to compute the medial axis of any closed, bounded and regular planar domain. Importantly, our approach can generate the medial axis, the straight skeleton, and the C-skeleton of possibly deformable shapes within the same formulation, extends naturally to 3D, and can be used in a variety of applications such as skeleton-based shape editing and adaptive motion planning.     

Medial axis computation for planar free-form shapes

We present a simple, efficient, and stable method for computing—with any desired precision—the medial axis of simply connected planar domains. The domain boundaries are assumed to be given as polynomial spline curves. Our approach combines known results from the field of geometric approximation theory with a new algorithm from the field of computational geometry. Challenging steps are (1) the approximation of the boundary spline such that the medial axis is geometrically stable, and (2) the efficient decomposition of the domain into base cases where the medial axis can be computed directly and exactly. We solve these problems via spiral biarc approximation and a randomized divide & conquer algorithm.     

Direct boolean intersection between acquired and designed geometry

In this paper, a new shape modeling approach that can enable direct Boolean intersection between acquired and designed geometry without model conversion is presented. At its core is a new method that enables direct intersection and Boolean operations between designed geometry (objects bounded by NURBS and polygonal surfaces) and scanned geometry (objects represented by point cloud data).We use the moving least-squares (MLS) surface as the underlying surface representation for acquired point-sampled geometry. Based on the MLS surface definition, we derive closed formula for computing curvature of planar curves on the MLS surface. A set of intersection algorithms including line and MLS surface intersection, curvature-adaptive plane and MLS surface intersection, and polygonal mesh and MLS surface intersection are successively developed. Further, an algorithm for NURBS and MLS surface intersection is then developed. It first adaptively subdivides NURBS surfaces into polygonal mesh, and then intersects the mesh with the MLS surface. The intersection points are mapped to the NURBS surface through the Gauss-Newton method.Based on the above algorithms, a prototype system has been implemented. Through various examples from the system, we demonstrate that direct Boolean intersection between designed geometry and acquired geometry offers a useful and effective means for the shape modeling applications where point-cloud data is involved.     

改进的形态学骨架提取算法

针对由传统最大圆盘骨架提取算法提取出的骨架连通性差且无法保持一致的单像素宽度问题,提出一种改进的形态学骨架提取算法。将连通性保持与形态学运算相结合,在收缩目标提取骨架的过程中通过引入虚拟骨架点实现骨架曲线连通性保持,而单像素宽度细化及伪分支剔除等后处理过程的引入则进一步提高骨架描述目标形状及拓扑特征的能力。相关仿真研究证明了该算法的有效性。