曲面立体线图的补线技术研究

文中根据已有的曲面立体自然线图的标记原理，得到了曲面立体画隐线图的标记原理和方法。曲面立体的不完整线图中的L型节点是曲面立体完整线图中W型节点的退化。基于曲面立体画出隐藏线的完整线图标记原理和方法，详细分析并建立了曲面立体不完整线图中L型节点与曲面立体完整线图中W型节点的对应关系。提出了曲面立体不完整线图的标记和补线方法，结合算例详细论述了曲面立体不完整线图的标记和补线过程，从曲面立体不完整线图获得了合理的曲面立体完整线图。     

线画图的外围轮廓线搜索和标记

研究线画图的外围轮廓线的搜索和标记方法.线图解释是计算机视觉研究中的主要任务之一,其中线画图标记是线图解释中的一个重要问题.线画图包含了三维物体的许多信息.根据sugihara[1]阐述的标记过程可知,外围轮廓线的标记是进行线画图标记的至关重要的一步.本文运用坐标变换方法比较图线与X轴夹角,获取了线画图外围轮廓线,并按照标记规则进行标记.线画图外围轮廓线的标记过程如下首先确定线画图外围轮廓线的起始点,由起始点开始进行查找与之相连的边;接着计算该相邻的边与X轴夹角,最大夹角所对应的边即为轮廓线;最后当终点和起点重合时,整个搜索过程结束并完成外轮廓线的标记.用实验进行验证,结果表明该方法是有效的.     

基于面向对象的线画图立体图形的实体模型设计

文中应用面向对象的设计方法，针对消除隐藏线算法，为由点，直线段，多边形构成的立体图形设计了一种实体模型，该实体模型具有封装性和可维护性等面向对象设计方法的优点，同时由于记录了大量的立体图形的点、边、面的拓扑关系，使消除隐藏线算法减少很多已知点，边、面查找相关的点、边、面的运算，从而提高了算法的效率，使在显示进行平移，放缩，旋转等变换的立体图形时，可较好地满足消除隐藏线的实时性的要求。     

基于优化算法的从线画图精确重构三维物体

现有的基于优化算法的三维物体重构方法只能将线画图重构为“粗糙”的三维物体,从而限制了这些方法的实际应用.为此提出一种基于优化算法的改进方法,该方法分2个阶段实现:第一阶段通过在目标函数中引入膨胀-规整平衡因子λ,利用λ的变化渐近优化得到线画图的初步重构结果;第二阶段重构使用不等式约束逐步逼近平行、垂直、共面的等式约束,利用非线性约束优化算法首先精确地重构出三维物体的主平面,然后得到其他非主平面顶点的精确三维坐标,完成整个线画图的精确重构.实验结果表明,文中方法有效和稳定,其重构结果的精度明显优于现有方法.     

叶片截面不规则叶轮零件的反求设计

一、引言叶轮是压力集中的关键零件，其工作转速高，零件形状复杂，特别是它的流道型面的形状及精度对提高增压器的性能具有决定性的影响。其设计的先进性直接影响整机性能。叶轮叶片的曲面形状多由反复实验确定，叶轮批量生产之前，必须将试验样品反求成三维实体。复杂叶轮零件对曲面要求较高，要求至少保证叶片曲面空间一阶连续（相切）。小型叶轮为保证工作效率，大小叶片间隔排列，且叶片不等厚，大小叶片形状不一致（变化规律不同），叶片的厚度随叶片的延伸相应变化。叶片曲面构成主要有两种方式，一种是直纹面，截面线是直线（如图1…     

结合分类卷积神经网络和形状上下文的线画图检索

传统线画图检索中仅仅利用线画图形状特征信息导致检索准确率不高,为了高效、准确地从线画图数据集中检索相似的线画图,提出一种结合分类卷积神经网络和形状上下文的线画图检索方法.首先利用大卷积核的分类卷积神经网络对线画图像数据集进行分类训练任务得到神经网络权值参数,使用该网络结构提取数据集中每张线画图的卷积特征信息;然后根据用户在画图板上绘制得到的简单线画图输入,利用卷积神经网络进行二次分类得到前15种最相似的分类,并结合形状上下文算法对15种分类匹配相似度并取前8种分类;最后使用卷积神经网络提取用户输入的线画图特征信息并与8种分类中的线画图特征信息进行匹配,根据相似度大小排序得到线画图匹配结果.基于Caffe卷积神经网络开发框架,采用TU-Berlinsketchbenchmark线画图数据集进行实验的结果表明,该方法能高效、准确地从数据集中检索得到相似线画图,同时能保证检索结果集中于最相似的几种类别且同类型中能有更多的选择.     

基于画图算法的WSN节点定位算法

针对无线传感器网络的节点定位问题,提出一种新的基于类Kamada Kawai画图算法的无线传感器网络节点定位算法,将无线传感器网络节点定位问题转化成画图问题,用经典的画图算法求得问题的最优解,从而实现对节点的定位。仿真实验结果表明,该算法收敛速度快、定位精度高、能够获得较好的效果。     

圆柱与圆锥轴线相交时左侧相贯线上最右点的解析证明与图解

轴线相交的圆柱、圆锥两曲面立体相贯时,产生左右两条空间相贯线曲线。该文以左侧相贯线为研究对象,用数学方法证明圆柱立体的半径在一定范围内变化时,左侧相贯线上最右点的变化规律,由此提出了准确绘制左侧相贯线上最右点的图解方法。左侧相贯线上的最右点在两条特殊相贯线上,分别在锥和与锥相切的球的相贯线上及在柱和与锥相切的球的相贯线上。     

叶片截面不规则叶轮零件的反求设计

一、引言 　　叶轮是压力集中的关键零件,其工作转速高,零件形状复杂,特别是它的流道型面的形状及精度对提高增压器的性能具有决定性的影响.其设计的先进性直接影响整机性能.叶轮叶片的曲面形状多由反复实验确定,叶轮批量生产之前,必须将试验样品反求成三维实体.复杂叶轮零件对曲面要求较高,要求至少保证叶片曲面空间一阶连续(相切).……     

叶片截面不规则叶轮零件的反求设计

一、引言 叶轮是压力集中的关键零件,其工作转速高,零件形状复杂,特别是它的流道型面的形状及精度对提高增压器的性能具有决定性的影响.其设计的先进性直接影响整机性能.叶轮叶片的曲面形状多由反复实验确定,叶轮批量生产之前,必须将试验样品反求成三维实体.复杂叶轮零件对曲面要求较高,要求至少保证叶片曲面空间一阶连续(相切).     

Labeling Line Drawings with Hidden-Part-Drawn of Planar Object with Trihedral Vertices

Although line drawings consist of only line segments on a plane, they convey much information about the three-dimensional object structures. For a computer interpreting line drawings, some intelligent mechanism is required to extract three-dimensional information from the two-dimensional line drawings. In this paper, a new labeling theory and method are proposed for the two-dimensional line drawing with hidden-part-draw of a three-dimensional planar object with trihedral vertices. Some rules for labeling line drawing are established. There are 24 kinds of possible junctions for line drawing with hidden-part-draw, in which there are 8 possible Y and 16 W junctions. The three problems are solved that Sugihara's line drawing labeling technique exists. By analyzing the projections of the holes in manifold planar object, we have put forward a labeling method for the line drawing. Our labeling theory and method can discriminate between correct and incorrect hidden-part-draw natural line drawings. The hidden-part-draw natural line drawings can be labeled correctly by our labeling theory and method, whereas the labeling theory of Sugihara can only label the hidden-part-draw unnatural line drawings in which some visible lines must be drawn as hidden lines, and some invisible lines must be drawn as continuous lines.     

基于点线关系从透视画隐线图重构三维平面立体

提出了一种基于点与直线关系从透视投影画隐线图建立平面立体线框模型的新方法。给出了基于点线关系的基本约束,根据透视投影画隐线图中隐含的点与直线位置关系建立约束方程,建立一个线性系统,通过求解该线性系统得到平面立体的三维信息。用算例进行验证,得到了平面立体的三维信息。     

基于约束关系的平面立体三维重建

提出一种基于约束的平面立体三维重建算法。该算法采用参数化方式来表示空间直线及其投影,这种参数化方式能满足数字图像中直线提取所需的唯一性、有界性及均匀性条件。依据平面立体投影线图的拓扑结构隐含的三维信息,建立平面立体上棱线、表面空间位置参数之间的约束方程,联立约束方程组求其最小二乘解,恢复出平面立体的三维结构。研究成果可用于计算机视觉和智能CAD系统。     

Line drawing via saliency map and ETF

Line drawing is a means of superior visual communication which can effectively convey useful information to viewers. Artists usually draw what they see rather than what exists, which means the most attractive object is emphasized while the rest are inhibited. Moreover, artists draw the whole object with coherent lines instead of fractured lines, which also contribute to the outstanding visual effect. From these perspectives, generating line drawings with saliency and coherence remains a great challenge. Existing line drawing generation methods ignore these important properties and cannot generate coherent lines in some cases since they do not take into account how artists draw a picture. To this end, a novel saliency-aware line drawing method was proposed to better grasp the viewer’s attention on an image. First, a saliency enhanced line extraction method combining saliency map and edge tangent flow was proposed to ensure the saliency and coherence of lines, especially in salient but low contrast areas. Then, the salient information was highlighted while irrelevant details were eliminated by inhibiting lines in less salient areas to enhance the saliency of the line drawing. Finally, the transparency of lines was adjusted to further emphasize important information. Various results showed that our method can generate line drawings with better visual saliency and coherence than the state-of-the-art methods.     

Interpreting line drawings of curved objects

In this paper, we study the problem of interpreting line drawings of scenes composed of opaque regular solid objects bounded by piecewise smooth surfaces with no markings or texture on them. It is assumed that the line drawing has been formed by orthographic projection of such a scene under general viewpoint, that the line drawing is error free, and that there are no lines due to shadows or specularities. Our definition implicitly excludes laminae, wires, and the apices of cones.A major component of the interpretation of line drawings is line labelling. By line labelling we mean (a) classification of each image curve as corresponding to either a depth or orientation discontinuity in the scene, and (b) further subclassification of each kind of discontinuity. For a depth discontinuity we determine whether it is a limb—a locus of points on the surface where the line of sight is tangent to the surface—or an occluding edge—a tangent plane discontinuity of the surface. For an orientation discontinuity, we determine whether it corresponds to a convex or concave edge. This paper presents the first mathematically rigorous scheme for labelling line drawings of the class of scenes described. Previous schemes for labelling line drawings of scenes containing curved objects were heuristic, incomplete, and lacked proper mathematical justification.By analyzing the projection of the neighborhoods of different kinds of points on a piecewise smooth surface, we are able to catalog all local labelling possibilities for the different types of junctions in a line drawing. An algorithm is developed which utilizes this catalog to determine all legal labellings of the line drawing. A local minimum complexity rule—at each vertex select those labellings which correspond to the minimum number of faces meeting at the vertex—is used in order to prune highly counter-intuitive interpretations. The labelling scheme was implemented and tested on a number of line drawings. The labellings obtained are few and by and large in accordance with human interpretations.     

Line Drawing Vectorization via Coarse-to-Fine Curve Network Optimization

Vectorizing line drawings is a fundamental component of the workflow in various applications such as graphic design and computer animation. A practical vectorization tool is desired to produce high-quality curves that are faithful to the original inputs and close to the connectivity of human drawings. The existing line vectorization approaches either suffer from low geometry accuracy or incorrect connectivity for noisy inputs or detailed complex drawings. We propose a novel line drawing vectorization framework based on coarse-to-fine curve network optimization. Our technique starts with an initial curve network generated by an existing tracing method. It then performs a global optimization which fits the curve network to image centrelines. Finally, our method performs a finer optimization in local junction regions to achieve better connectivity and curve geometry around junctions. We qualitatively and quantitatively evaluate our system on line drawings with varying image quality and shape complexity, and show that our technique outperforms existing works in terms of curve quality and computational time.     

Frontal geometry from sketches of engineering objects: is line labelling necessary?

A tool which can quickly interpret line drawings (with hidden lines removed) of engineering objects as boundary representation CAD models would be of significant benefit in the process of engineering design. Inflation of the drawing to produce a frontal geometry, a geometric realisation of that part of the object visible in the drawing, is an important stage of this process.Previous methods of producing frontal geometries have relied on the technique of line labelling (labelling edges as convex, concave or occluding). Although restricted subsets of the line-labelling problem have known solutions, reliable methods have not been found for the general line-labelling problem, and traditional methods, when adapted to drawings with non-trihedral junctions, are unacceptably slow.Many other papers assume that line labelling is an essential step. Here, we show this is not necessarily true, and that comparable results can be obtained by a novel alternative approach. Firstly, we consider what outputs from line labelling are essential to the production of frontal geometry. Secondly, we investigate by what other means these outputs can be produced.Our work indicates that the only essential output from line labelling for frontal geometry is the determination of which T-junctions in a drawing are occluding and which are non-occluding. This information is required for inflation, and also for detection of symmetry and for constructing hidden topology.Thus, we propose and analyse a new method which, in the absence of line labels, simultaneously inflates a drawing to produce the frontal geometry and attempts to determine whether each T-junction is occluding or not. For drawings of objects with holes or pockets, and for cases where line labelling is particularly unreliable, our new method can provide a better alternative.     

The Interpretation of Line Drawings with Contrast Failure and Shadows

In line drawings derived from real images, lines may be missing due to contrast failure and objects with curved surfaces may cast shadows from multiple light sources.This paper shows that it is the presence of shadows, rather than contrast failure, that renders the line drawing labelling problem NP-complete. However, shadows are a valuable visual cue, since their presence is formally shown to reduce the average ambiguity of drawings. This is especially true when constraints concerning shadow formation are employed to differentiate shadow and non-shadow lines.The extended junction constraint, concerning straight lines colinear with junctions, compensates the loss of information caused by contrast failure. In fact, we observe the contrast failure paradox: a drawing is sometimes less ambiguous when lines are partly missing due to contrast failure.It is known that the coplanarity of sets of object vertices can be deduced from the presence of straight lines in the drawing. This paper shows that these coplanarity constraints are robust to the presence of contrast failure.     

On the complexity of labeling perspective projections of polyhedral scenes

This paper investigates the computational time complexity of the labeling problem for line drawings of trihedral scenes. It is shown that the class of problems having polynomial complexity is larger than the simple case of line drawings of Legoland scenes (Kirousis and Papadimitriou, 1988). Once the location of the vanishing points in the image plane is known, the labeling problem can be solved in time O(Nn) where N is the number of segments and n is the number of vanishing points. The vanishing points can be given a priori, otherwise can, in many cases, be detected by standard techniques from the line drawing itself. The NP-completeness of the labeling problem for line drawings of trihedral scenes (Kirousis and Papadimitriou, 1988) is then due to the lack of knowledge about the vanishing points. which is equivalent to the knowledge of the possible directions for the edges. These results help draw a more accurate boundary between the problems in the interpretation of line drawings that are polynomially solvable and those that are NP-complete.