Topology authentication for piping isometric drawings

Piping isometric drawings, which feature their intrinsical topological relation rather than just geometrical shape, are important industrial art works in the field of Computer-Aided Design (CAD). This paper takes a fresh look at the topology integrity authentication of piping isometric drawings, which has not been mentioned before in the literature, from the digital watermarking perspective. A blind and semi-fragile watermarking based algorithm is proposed to address the referred interesting issue. The topology authentication problem of piping isometric drawings is investigated. In addition to the stretching operation, both global and local similarity transformation operations, which are critical problems in the case of watermarking embedding and extraction, are analyzed in detail. The topological graph is extracted and constructed from the drawing firstly. Then, similarity transformation invariants are constructed as watermarks carriers for each node. After that, the topological relation among joint components is encoded into singular watermarks for each node of the graph. These generated topology sensitive watermarks are embedded into geometrical invariants of each node via quantization index modulation. Theoretical analysis and experimental results demonstrate that our approach yields a strong ability in detecting and locating unauthorized topology attacks while achieves robustness against both global and local similarity transformations especially the stretching operation. The proposed scheme can be employed to authenticate topology integrity for each of the drawings derived from the model individually in industry practices.     

Viewpoint independent matching of planar curves in 3D space

We present a new approach to match planar curves using the weak perspective projection model. This is based on a set of shape parameters that can be extracted from a closed or open contour, derived from the original image as a θ(s) boundary code. In order to reduce the complexity and increase the robustness of the matching process, the original parameters are reduced to a set of three intermediate variables, each of which can be calculated independently. These variables are contained within a system of linear equations which define the angles and the ratio of the heights of corresponding point pairs on the two contours with respect to a floating coordinate system. The shape matching process is scale and orientation independent, and the original parameters that describe the relative pose of the two contours in 3D space can be recovered subsequently. The approach can be applied to “featured” and “featureless” contours, to whole and partial contours, and is demonstrated on images of contours and mechanical parts and tools to recover identity and pose.     

基于形状演化的线条画风格转换与变形

根据线条画和线条画中笔画的形状特征，运用平面形状演化理论对线条画和笔画的形状进行平滑或增强，并对宽度进行相应的调整，最后得到不同风格的线条画．该风格转换水需要任何样本，而且能够控制转换的程度，提高了线条画风格转换的自由度．     

基于图形识别的剪力墙标注方法

根据剪力墙施工图的特点，提出了基于图形形状识别的剪力墙尺寸标注方法。通过对剪力墙图形特点的分析，在现有图形识别方法的基础上，结合人工智能和模式识别在图形分析中的应用，提出了区域关系的图形识别方法，建立了一个可以不断学习新形状的图形模板库。通过图形间的匹配关系来进行剪力墙尺寸标注，从而大大提高了剪力墙尺寸标注的合理性。     

Para-Graph: Graph-Based Parameterization of Triangle Meshes with Arbitrary Genus

This paper describes a novel approach to the parameterization of triangle meshes representing 2‐manifolds with an arbitrary genus. A topology‐based decomposition of the shape is computed and used to segment the shape into primitives, which define a chart decomposition of the mesh. Then, each chart is parameterized using an extension of the barycentric coordinates method. The charts are all 0‐genus and can be of three types only, depending on the number of boundary components. The chart decomposition and the parameterization are used to define a shape graph where each node represents one primitive and the arcs code the adjacency relationships between the primitives. Conical and cylindrical primitives are coded together with their skeletal lines that are computed from and aligned with their parameterization. The application of the parameterization approach to remeshing guarantees that extraordinary vertices are localized only where two patches share a boundary and they are not scattered on the whole surface.     

A Generic Integrated Line Detection Algorithm and Its Object–Process Specification

A generic integrated line detection algorithm (GILDA) is presented and demonstrated. GILDA is based on the generic graphics recognition approach, which abstracts the graphics recognition as a stepwise recovery of the multiple components of the graphic objects and is specified by the object–process methodology. We define 12 classes of lines which appear in engineering drawings and use them to construct a class inheritance hierarchy. The hierarchy highly abstracts the line features that are relevant to the line detection process. Based on the “Hypothesis and Test” paradigm, lines are detected by a stepwise extension to both ends of a selected first key component. In each extension cycle, one new component which best meets the current line's shape and style constraints is appended to the line. Different line classes are detected by controlling the line attribute values. As we show in the experiments, the algorithm demonstrates high performance on clear synthetic drawings as well as on noisy, complex, real-world drawings.     

基于面形位编码的CAD模型检索

提出一种基于面形位码的模型检索方法.计算模型中任意面f的形位码分为2步.首先根据实体的B-rep结构生成属性邻接图并将图转化为以面f为中心的层状结构;然后根据图的层状结构对每一层进行递归的编码,形成一种分阶的形位码.根据模型中所有面的形位码构造一个表达模型整体形状的描述矩阵,利用该矩阵可以有效地评估模型之间不同精度要求下的相似度,从而实现模型检索.实验结果表明,该方法不但具有较高的搜索效率,并且能根据不同精度的要求搜索到合适的相似模型.     

Structure-oriented contour representation and matching for engineering shapes

Conventional shape matching for engineering models primarily considers rigid shape similarity. They do not seek global shape similarity while considering large local deformations. However, engineering models created by some parametric-based design can involve large parametric changes. As a result, they do not share similarity in their global shape. Hence our goal is to develop shape representations for global matching of part models that can have large dissimilarity through stretching and/or bending.This paper presents a strategy of an integrated shape matching for contours of engineering drawings inspired by the divide-and-conquer paradigm. The original shape is decoupled into two levels of shape representations namely, higher-level structure and lower-level geometry. The higher-level structure matching is then achieved driven by optimal integrated solutions from matching of lower-level local geometry. Feature points are first extracted using curve evolution to attain the two levels of representations. In order to suit engineering semantics, a new significance function for a point is defined to suppress small features using discrete curve evolution. To conduct the integrated shape matching, a mechanism of using lookup tables is employed to associate these two levels of representations. Dynamic Time Warping and Elastic Matching are employed at different levels of shape representations in order to achieve the optimal integration.To demonstrate the advantages of the proposed work for engineering shapes, experiments for contour evolution, feature point registration, and shape-based similarity for retrieval are conducted. They are also compared with the existing methods. The experimental results show that the structure-oriented contour representation and matching are more meaningful and consistent from an engineering perspective.     

Interpretation of an axonometric projection of a polyhedron

This paper addresses some problems in interpretation of axonometric line drawings of polyhedrons, especially the problems of how much and what kind of further information is necessary to reconstruct uniquely the shape of objects from their axonometric line drawings. For line drawings which are precise, in the sense that vertices are drawn in correct position, the problems can be treated in terms of linear algebra, and a method for solving them is established. When line drawings are roughly drawn, on the other hand, the problems are much more difficult; a solution based on some combinatorial technique is given to a restricted object world in which each vertex lies on exactly three faces.     

T形汉字码输入法

T形汉字码输入法的提出,目的是提供一种易学易用、汉字部件规范直观、取码规则合理、重码率低、能够高速盲打或听打的计算机汉字编码输入法。它由拼音码和形部编码两部分组成,形部编码优选28个左右的多笔画部件和5种基本笔画,形部编码的取码规则规定为:左右结构的汉字,分别按书写顺序取该汉字的左部和右部的第一个基本部件的代码进行编码;非左右结构的汉字,按书写顺序取该汉字的第一个和最末一个基本部件的代码编码。     

基于径向基概率神经网络的工程图纸图形符号识别

基于径向基概率神经网络，提出一种扫描工程图纸图像分割后的图形符号识别方法，针对已分割的扫描工程图纸图形符号图像，首先进行二值化处理，然后对二值图形符号图像进行Hu不变矩特征提取，再使用一种新型的径向基概率神经网络进行分类，从而实现图像识别．为加快径向基概率神经网络的收敛速度，采用递归最小二乘算法进行训练．实验结果表明，径向基概率神经网络在识别性能与速度等方面非常适合于工程图纸的图形符号识别。     

Eliminate flowchart drawings

The difficulties in creating clean programming flowcharts and of generating good code from them are reviewed, and the line of thought is shown which leads to the elimination of drawings from the programming process. Benefits are cited.     

工程图扫描图象中交叉区域识别处理方法的研究

利用工程图样扫描图象的整体形状特性及图面在内容关联性的特点,深入分析了基于条块图的结点的形态结构,阐述了扫描图象线条交叉区域的识别处理方法。     

基于面域理解的多面体三维重建

已有的三维重建算法一般是从点线或体的角度来理解视图,实际上,视图中的环包含了 大量的形体面信息,可以直接从中间层次的面理解形体的投影。文中根据实体构成和平面投影的约束和规则重建显式表达的面,并进一步推导出隐式表达的面,从而得到完整的形体边界模型,本算法适用于平面多面体,通过面域作为中介,容易实现与模型引导方法的融合,从而拓展到二次曲面体的重建。     

On-Line Shape recognition with incremental training using binary synaptic weights algorithm

Recognition of hand drawn shapes is beneficial in drawing packages and automated sketch entry in handheld computers. In this paper, we propose a new approach to on-line geometric shape recognition with incremental training function, which utilizes a heuristic function to reduce noise and a neural network for classification and on-line training. Instead of recognizing segments of a drawing and then performing syntactical analysis to match with a predefined shape, which is weak in terms of generalization and dealing with noise, we examine the shape as a whole. The main concept of the recognition method is derived from the fact that internal angles are very important in the perceived shape of outlines. Our application's aim is to recognize elliptic, rectangular, and triangular shapes in a way similar to human cognition of these shapes. Human beings recognize such basic shapes regardless of the variations in size, noise on the shape border, rotation and in the case of triangles, regardless of the type of the triangle. The key concept is that the neural network learns the relationships between the internal angles of a shape and its classification, therefore only a few training samples which represent the class of the shape are sufficient. Fast meremental training, which is performed on-line, is accomplished by the use of the Binary Synaptic Weights algorithm, a one pass, feedforward neural network training algorithm. Incremental training offers the advantage of adjusting the recognition capability of the system to the user's drawings. the results are very successful, such that the neural network correctly classified shapes that did not have any resemblance to the shapes in the initial training set.     

3D reconstruction of complex curved objects from line drawings

An active research topic in computer vision and graphics is developing algorithms that can reconstruct the 3D surface of curved objects from line drawings. There are a number of algorithms have been dedicated to solve this problem, but they can't solve this problem when the geometric structure of a curved object becomes complex. This paper proposes a novel approach to reconstructing a complex curved 3D object from single 2D line drawings. Our approach has three steps:(1) decomposing a complex line drawing into several simpler line drawings and transforming them into polyhedron;(2) reconstructing the 3D wireframe of curved object from these simpler line drawings and generating the curved faces;(3) combining the 3D objects into the complete objects. A number of examples are given to demonstrate the ability of our approach to successfully perform reconstruction of curved objects which are more complex than previous methods.     

量点法做透视图规律的提出

透视图是描述工程形体的一种立体图。透视图画法很多,但它的画法一般来说都比较繁琐,不宜掌握,量点法作为透视图最常用的基本画法之一,也是如此。本文作者结合多年的教学经验,总结出根据透视要素按所属量点去画透视图中基透视的规律,以便大家能更好、更快地掌握透视图的画法。