Identification of faces in a 2D line drawing projection of awireframe object

An important key to reconstructing a three-dimensional object depicted by a two-dimensional line drawing projection is face identification. Identification of edge circuits in a 2D projection corresponding to actual faces of a 3D object becomes complex when the projected object is in wireframe representation. This representation is commonly encountered in drawings made during the conceptual design stage of mechanical parts. When nonmanifold objects are considered, the situation becomes even more complex. This paper discusses the principles underlying face identification and presents an algorithm capable of performing this identification. Face-edge-vertex relationships applicable to nonmanifold objects are also proposed. Examples from a working implementation are given     

智能装配机器人机械零件知识库的自动建立

为了实现智能装配机器人能够模拟人装配机械零件,系统应包含有关装配所必需的知识.利用这些知识,机器人自动编制装配工艺规程.并自动安排机器人的一系列控制命令.机械零件知识库是基于知识的智能装配机器人规划系统中不可缺少的知识.本文介绍了由机器人的视觉系统摄入机械零件图纸后,如何由摄入的二值化图形自动建立机械零件知识库.     

Multi-scale 2D tracking of articulated objects using hierarchical spring systems

This paper presents a flexible framework to build a target-specific, part-based representation for arbitrary articulated or rigid objects. The aim is to successfully track the target object in 2D, through multiple scales and occlusions. This is realized by employing a hierarchical, iterative optimization process on the proposed representation of structure and appearance. Therefore, each rigid part of an object is described by a hierarchical spring system represented by an attributed graph pyramid. Hierarchical spring systems encode the spatial relationships of the features (attributes of the graph pyramid) describing the parts and enforce them by spring-like behavior during tracking. Articulation points connecting the parts of the object allow to transfer position information from reliable to ambiguous parts. Tracking is done in an iterative process by combining the hypotheses of simple trackers with the hypotheses extracted from the hierarchical spring systems.     

A 3D shape segmentation approach for robot grasping by parts

Neuro-psychological findings have shown that human perception of objects is based on part decomposition. Most objects are made of multiple parts which are likely to be the entities actually involved in grasp affordances. Therefore, automatic object recognition and robot grasping should take advantage from 3D shape segmentation. This paper presents an approach toward planning robot grasps across similar objects by part correspondence. The novelty of the method lies in the topological decomposition of objects that enables high-level semantic grasp planning.In particular, given a 3D model of an object, the representation is initially segmented by computing its Reeb graph. Then, automatic object recognition and part annotation are performed by applying a shape retrieval algorithm. After the recognition phase, queries are accepted for planning grasps on individual parts of the object. Finally, a robot grasp planner is invoked for finding stable grasps on the selected part of the object. Grasps are evaluated according to a widely used quality measure. Experiments performed in a simulated environment on a reasonably large dataset show the potential of topological segmentation to highlight candidate parts suitable for grasping.     

Reprint of: Multi-scale 2D tracking of articulated objects using hierarchical spring systems

This paper presents a flexible framework to build a target-specific, part-based representation for arbitrary articulated or rigid objects. The aim is to successfully track the target object in 2D, through multiple scales and occlusions. This is realized by employing a hierarchical, iterative optimization process on the proposed representation of structure and appearance. Therefore, each rigid part of an object is described by a hierarchical spring system represented by an attributed graph pyramid. Hierarchical spring systems encode the spatial relationships of the features (attributes of the graph pyramid) describing the parts and enforce them by spring-like behavior during tracking. Articulation points connecting the parts of the object allow to transfer position information from reliable to ambiguous parts. Tracking is done in an iterative process by combining the hypotheses of simple trackers with the hypotheses extracted from the hierarchical spring systems.     

三维物体识别研究进展

出于工业和医疗等领域大量现实应用的需要,如今三维物体识别已成为一个很活跃的研究领域。一般来说,三维物体识别系统可以通过两个阶段的处理来完成三维物体的识别和定位,首先用传感器获取的场景输入数据来得到场景的表达;然后将它与数据库中存储的物体表达相匹配。为了推动该领域研究进一步发展,因而对近１０ａ年中该识别过程中必须解决的感传器类型、三维物体表达方法和匹配策略等３个方面问题的研究成果进行了综述,对主要方法进行分类和总结;并提出了一些三维视觉系统中还需要深入研究的问题,包括对所研究物体形状的限制、复杂背景的影响和表达以及识别中的“整体和局部”的矛盾等。     

Acquisition of 2D Shape Models from Scenes with Overlapping Objects using String Matching

In this paper we describe a system that is able to acquire models of 2D shapes from cluttered scenes. The input of the system is a sequence of images, each of which shows an unknown number of overlapping unknown 2D objects. The system identifies matching partial shapes across different images and combines them into complete 2D shape models, thus giving a complete interpretation of the input scenes. The identification of partial shapes is based on string matching, whereas a graph search procedure is used for shape model generation. The system has been fully implemented and tested on images containing parts of a jigsaw puzzle. Received: 20 November 1998?Received in revised form: 24 December 1998?Accepted: 4 January 1999     

BONSAI: 3D object recognition using constrained search

BONSAI, a model-based 3D object recognition system, is described. It identifies and localizes 3D objects in range images of one or more parts that have been designed on a computer-aided-design (CAD) system. Recognition is performed via constrained search of the interpretation tree, using unary and binary constraints (derived automatically from the CAD models) to prune the search space. Attention is focused on the recognition procedure, but the model-building, image acquisition, and segmentation procedures are also outlined. Experiments with over 200 images demonstrate that the constrained search approach to 3D object recognition has an accuracy comparable to that of previous systems     

Strategies of Multi-view and Multi-matching for 3D Object Recognition

A multi-view representation scheme and a multi-matching strategy for 3D object recognition are described; 3D objects are represented in terms of their 2D appearances so that 2D techniques can be applied to 3D recognition. Appearances of objects in the representation scheme are further organized in a hierarchical manner so that the matching process can reduce its search space by examining only the optimal view at every level of the representation scheme. In our multi-matching strategy, the matching module is composed of four components: point matcher, string matcher, vector matcher, and chamfer matcher. Each matcher is associated with a termination rule so that impossible views can be rejected at the early stages of the matching process. Experimental results reveal that the proposed strategies are feasible for 3D object recognition.     

二维空间对象空间关系的定性表示

主要研究了二维空间中空间对象间关系的定性表示。介绍了基于RCC的拓扑关系定性表示,讨论了方向关系的定性表示,给出了一个将拓扑关系定性表示和方向关系定性表示相结合的定性表示模型——SR表示模型。     

3D C-string: a new spatio-temporal knowledge representation for video database systems

In video database systems, one of the most important methods for discriminating the videos is by using the objects and the perception of spatial and temporal relations that exist between objects in the desired videos. In this paper, we propose a new spatio-temporal knowledge representation called 3D C-string. The knowledge structure of 3D C-string, extended from the 2D C⁺-string, uses the projections of objects to represent spatial and temporal relations between the objects in a video. Moreover, it can keep track of the motions and size changes of the objects in a video. The string generation and video reconstruction algorithms for the 3D C-string representation of video objects are also developed. By introducing the concept of the template objects and nearest former objects, the string generated by the string generation algorithm is unique for a given video and the video reconstructed from a given 3D C-string is unique too. This approach can provide us an easy and efficient way to retrieve, visualize and manipulate video objects in video database systems. Finally, some experiments are performed to show the performance of the proposed algorithms.     

Embodied interaction with a 3D versus 2D mobile map

In comparison to 2D maps, 3D mobile maps involve volumetric instead of flat representation of space, realistic instead of symbolic representation of objects, more variable views that are directional and bound to a first-person perspective, more degrees of freedom in movement, and dynamically changing object details. We conducted a field experiment to understand the influence of these qualities on a mobile spatial task where buildings shown on the map were to be localized in the real world. The representational differences were reflected in how often users interact with the physical environment and in when they are more likely to physically turn and move the device, instead of using virtual commands. 2D maps direct users into using reliable and ubiquitous environmental cues like street names and crossings, and 2D better affords the use of pre-knowledge and bodily action to reduce cognitive workload. Both acclaimed virtues of 3D mobile maps—rapid identification of objects and ego-centric alignment—worked poorly due reasons we discuss. However, with practice, some 3D users learned to shift to 2D-like strategies and could thereby improve performance. We conclude with a discussion of how representational differences in mobile maps affect strategies of embodied interaction. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A contour tracing and coding algorithm for generating 2D contour codes from 3D classified objects

In 3D image data sets generated by voxel-based classification, each voxel is marked with a specific class label. Voxels of the same class label can form 3D objects of extremely complex shape. Interactively drawn regions are usually represented by their 2D region borders. In order to combine automatically classified with interactively drawn regions, a contour tracing and coding algorithm for generating optimized 2D contours from 3D classified objects is presented. A special conversion algorithm allows a chain or a crack code representation. An application to medical images shows the method's necessity and usefulness in dealing with highly complex regions.     

An efficient algorithm for attention-driven image interpretation from segments

In the attention-driven image interpretation process, an image is interpreted as containing several perceptually attended objects as well as the background. The process benefits greatly a content-based image retrieval task with attentively important objects identified and emphasized. An important issue to be addressed in an attention-driven image interpretation is to reconstruct several attentive objects iteratively from the segments of an image by maximizing a global attention function. The object reconstruction is a combinational optimization problem with a complexity of 2^N which is computationally very expensive when the number of segments N is large. In this paper, we formulate the attention-driven image interpretation process by a matrix representation. An efficient algorithm based on the elementary transformation of matrix is proposed to reduce the computational complexity to 3ωN(N-1)²/2, where ω is the number of runs. Experimental results on both the synthetic and real data show a significantly improved processing speed with an acceptable degradation to the accuracy of object formulation.     

Dynamic integration of height maps into a 3D world representation from range image sequences

Integration of 21/2D sketches obtained at different observation stations into a consistent world (or object) representation is one of the central issues in computer vision and robotics. The resolution and accuracy of 21/2D sketches may be different from one view point to another, and inconsistent data between different observations may occur. This article presents an approach to building a spatiotemporal representation of dynamic scenes including moving objects from a sequence of range images taken by a moving observer. A range image is transformed into a height-map representation, which is segmented into the ground plane and objects on it. In order to capture the resolution and accuracy of the range information and the consistency of the height information between different height maps, we define a reliability measure of the height information for each bucket on the height map. Using this reliability, the system finds the correspondences of both static and moving objects between different observations, and successively refines the height information and its reliability with newly acquired data, dealing with inconsistent data. Final representation of the integrated height map consists of the time stamp of the last observation, region labels of static and moving objects and their spatiotemporal properties such as height information, its reliability, and the velocities of both the observer and independently moving objects. We applied the method to road scenes physically simulated by landscape toy models and show the experimental results.     

Virtual reality movies-real-time streaming of 3D objects

Powerful servers for computation and storage, high-speed networking resources, and high-performance 3D graphics workstations, which are typically available in scientific research environments, potentially allow the development and productive application of advanced distributed high-quality multimedia concepts. Several bottlenecks, often caused by the inefficient design and software implementation of current systems, prevent utilization of the offered performance of existing hardware and networking resources. We present a system architecture, which supports streamed online presentation of series of 3D objects. In the case of expensive simulations on a supercomputer, results are increasingly represented as 3D geometry to support immersive exploration, presentation, and collaboration techniques. Accurate representation and high-quality display are fundamental requirements to avoid misinterpretation of the data. Our system consists of the following parts: a preprocessor to create a special 3D representation – optimized under transmission and streamed presentation issues in a high-performance working environment, an efficiently implemented streaming server, and a client. The client was implemented as a web browser plugin, integrating a viewer with high-quality virtual reality presentation (stereoscopic displays), interaction (tracking devices), and hyperlinking capabilities.