Global localization for mobile robots using reference scan matching

This paper presents a new approach based on scan matching for global localization with a metric-topological hybrid world model. The proposed method aims to estimate relative pose to the most likely reference site by matching an input scan with reference scans, in which topological nodes are used as reference sites for pose hypotheses. In order to perform scan matching we apply the spectral scan matching (SSM) method that utilizes pairwise geometric relationships (PGR) formed by fully interconnected scan points. The SSM method allows the robot to achieve scan matching without using an initial alignment between two scans and geometric features such as corners, curves, or lines. The localization process is composed of two stages: coarse localization and fine localization. Coarse localization with 2D geometric histogram constructed from the PGR is fast, but not precise sufficiently. On the other hand, fine localization using the SSM method is comparatively slow, but more accurate. This coarse-to-fine framework reduces the computational cost, and makes the localization process reliable. The feasibility of the proposed methods is demonstrated by results of simulations and experiments.     

一种基于Morlet小波变换的虹膜识别算法

虹膜识别包括虹膜定位、特征提取以及模式匹配几个步骤。文章提出了基于虹膜灰度梯度分析的新定位算法和基于Morlet小波变换的特征提取算法。首先对沿瞳孔半径方向展开的虹膜图像通过寻找灰度梯度最大值位置的方法进行虹膜定位;然后根据虹膜生理的特点对虹膜图像进行分区,对不同的虹膜区域采用一维和二维Morlet复小波变换相结合的特征提取算法,并用二比特格雷编码来表征提取的虹膜纹理的相位信息;最后通过计算虹膜间的Hamming距进行匹配,最终实现虹膜识别。实验结果表明,与现有算法相比,该算法识别速度快,提取特征的效果好,在实验室身份认证系统中表现出很好的识别效果。     

虹膜定位

为了提高虹膜定位的速度以及虹膜定位算法的健壮性,提出了一种粗定位与精定位相结合的两步定位法,用以进行虹膜定位,并对现有的虹膜定位算法进行了一些改进,实验结果表明,用两步法进行虹膜定位可以加快定位速度,减少搜索计算的盲目性。     

机械臂视觉伺服系统中的高精度实时特征提取

以机械臂视觉伺服系统为背景,立体视觉所需要的特征点为目标,提出一种基于颜色块的实时特征提取方法．特征点的定位分为粗定位和精定位两个过程,粗定位用来跟踪目标颜色块,精定位在粗定位的基础上,切出小图像并提取目标轮廓,利用犓犔变换对轮廓点进行分类,并通过最小二乘法对边缘点进行拟合．根据直线方程计算顶点的亚像素精度坐标,为下一步的目标位姿测量提供基础．实验结果验证了该方法的有效性．     

Observation‐driven Bayesian Filtering for Global Location Estimation in the Field Area

Global localization has long been considered one of the most important but also one of the most challenging localization problems for mobile robots. Current studies of global localization in the literature are mainly based on the Bayesian filtering technique, which can provide an elegant statistical framework for uncertainty management and multisensory fusion. However, the majority of implementations of Bayesian filters for global localization obey the same update rules in such a location‐driven sense that they guess the robot location first and then adjust the guess by incorporating the current observation data. This leads to some problematic consequences in that the system suffers from great computational load in a large application area and it cannot recover from localization failure. To overcome the above limitations, this paper deviates from the conventional update rules of Bayes filters and proposes a new approach: the observation‐driven Bayes filters (OD‐BFs). As the name implies, OD‐BFs estimate the robot state just according to the most recent observations and then adjust the estimate by incorporating the dead‐reckoning information. We further implement an observation‐driven Bayes filter to globally estimate the robot pose in the field area. This global localization system features an effective pose estimation framework that can operate with a large amount of point data in a coarse‐to‐fine manner. Sufficient experiments were carried out to determine both the advantages and the disadvantages of our OD‐BF localization approaches compared with previous ones.     

Hand-held 3D scanning based on coarse and fine registration of multiple range images

A hand-held 3D scanning technique is proposed to reconstruct 3D models of real objects. A sequence of range images captured from a hand-held stereo camera is automatically registered to a reference coordinate system. The automated scanning process consists of two states, coarse and fine registration. At the beginning, scanning process starts at the fine registration state. A fast and accurate registration refinement technique is used to align range images in a pair-wise manner. If the refinement technique fails, the process changes to the coarse registration state. A feature-based coarse registration technique is proposed to find correspondences between the last successful frame and the current frame. If the coarse registration successes, the process returns to the fine registration state again. A fast point-to-plane refinement technique is employed to do shape-based registration. After the shape-based alignment, a texture-based refinement technique matches texture features to enhance visual appearance of the reconstructed models. Through a graphic and video display, a human operator adjusts the pose of the camera to change the view of the next acquisition. Experimental results show that 3D models of real objects are reconstructed from sequences of range images.     

Hierarchical palmprint identification via multiple feature extraction

Biometric computing offers an effective approach to identify personal identity by using individual's unique, reliable and stable physical or behavioral characteristics. This paper describes a new method to authenticate individuals based on palmprint identification and verification. Firstly, a comparative study of palmprint feature extraction is presented. The concepts of texture feature and interesting points are introduced to define palmprint features. A texture-based dynamic selection scheme is proposed to facilitate the fast search for the best matching of the sample in the database in a hierarchical fashion. The global texture energy, which is characterized with high convergence of inner-palm similarities and good dispersion of inter-palm discrimination, is used to guide the dynamic selection of a small set of similar candidates from the database at coarse level for further processing. An interesting point based image matching is performed on the selected similar patterns at fine level for the final confirmation. The experimental results demonstrate the effectiveness and accuracy of the proposed method.     

Detection of microaneurysms using multi-scale correlation coefficients

This paper presents a new approach to the computer aided diagnosis (CAD) of diabetic retinopathy (DR)—a common and severe complication of long-term diabetes which damages the retina and cause blindness. Since microaneurysms are regarded as the first signs of DR, there has been extensive research on effective detection and localization of these abnormalities in retinal images. In contrast to existing algorithms, a new approach based on multi-scale correlation filtering (MSCF) and dynamic thresholding is developed. This consists of two levels, microaneurysm candidate detection (coarse level) and true microaneurysm classification (fine level). The approach was evaluated based on two public datasets—ROC (retinopathy on-line challenge, http://roc.healthcare.uiowa.edu) and DIARETDB1 (standard diabetic retinopathy database, http://www.it.lut.fi/project/imageret/diaretdb1). We conclude our method to be effective and efficient.     

Deep Deformation Detail Synthesis for Thin Shell Models

In physics-based cloth animation, rich folds and detailed wrinkles are achieved at the cost of expensive computational resources and huge labor tuning. Data-driven techniques make efforts to reduce the computation significantly by utilizing a preprocessed database. One type of methods relies on human poses to synthesize fitted garments, but these methods cannot be applied to general cloth animations. Another type of methods adds details to the coarse meshes obtained through simulation, which does not have such restrictions. However, existing works usually utilize coordinate-based representations which cannot cope with large-scale deformation, and requires dense vertex correspondences between coarse and fine meshes. Moreover, as such methods only add details, they require coarse meshes to be sufficiently close to fine meshes, which can be either impossible, or require unrealistic constraints to be applied when generating fine meshes. To address these challenges, we develop a temporally and spatially as-consistent-as-possible deformation representation (named TS-ACAP) and design a DeformTransformer network to learn the mapping from low-resolution meshes to ones with fine details. This TS-ACAP representation is designed to ensure both spatial and temporal consistency for sequential large-scale deformations from cloth animations. With this TS-ACAP representation, our DeformTransformer network first utilizes two mesh-based encoders to extract the coarse and fine features using shared convolutional kernels, respectively. To transduct the coarse features to the fine ones, we leverage the spatial and temporal Transformer network that consists of vertex-level and frame-level attention mechanisms to ensure detail enhancement and temporal coherence of the prediction. Experimental results show that our method is able to produce reliable and realistic animations in various datasets at high frame rates with superior detail synthesis abilities compared to existing methods.     

一种改进的虹膜定位方法

如何有效地确定虹膜在图象中的位置，是虹膜识别中需要解决的关键问题之一，在以前的粗定位与精定位相结合的两步虹膜定位方法的研究基础上，提出了一种改进的虹膜定位方法，它集中体现在虹膜粗定位方法的改进上，改进后的虹膜粗定位的基本思想为：首先在虹膜图像中选择互不相邻的若干行，求得每行的灰度差分曲线；然后根据灰度差分曲线上相邻几个点的累加和的大小，寻找虹膜或瞳孔的边界点；最后，由这些边界点拟合出虹膜及瞳孔的边界，实验结果表明，改进的虹膜定位方法更为快速、稳健。     

Features extraction from hand images based on new detection operators

Human hand shape features extraction from image frame sequences is one of the key steps in human hand 2D/3D tracking system and human hand shape recognition system. In order to satisfy the need of human hand tracking in real time, a fast and accurate method for acquirement of edge features from human hand images without consideration of hand over face is put forward in this paper. The proposed approach is composed of two steps, the coarse location phase (CLP) and the refined location phase (RLP) from coarseness to refinement. In the phase of CLP, the hand contour is approximately described by a polygon with concave and convex, an approach to obtaining hand shape polygon using locating points and locating lines is meticulously discussed. Then, a coarse location (CL) algorithm for extraction of interested hand shape features, such as contour, fingertips, roots of fingers, joints and the intersection of knuckle on different fingers, is proposed. In the phase of RLP, a multi-scale approach is introduced into our study to refine the features obtained by the CL algorithm. By means of defining the response strength of different types of features, a refined location (RL) algorithm is proposed. The major contribution of this paper is that the novel detection operators for features of hand images are presented in the above two steps, which have been successfully applied to our 3D hand shape tracking system and 2D hand shape recognition system. A number of comparative studies with real images and online videos demonstrate that the proposed method can extract the three defined human hand image features with high accuracy and high speed.     

CustomCut: On‐demand Extraction of Customized 3D Parts with 2D Sketches

Several applications in shape modeling and exploration require identification and extraction of a 3D shape part matching a 2D sketch. We present CustomCut, an on‐demand part extraction algorithm. Given a sketched query, CustomCut automatically retrieves partially matching shapes from a database, identifies the region optimally matching the query in each shape, and extracts this region to produce a customized part that can be used in various modeling applications. In contrast to earlier work on sketch‐based retrieval of predefined parts, our approach can extract arbitrary parts from input shapes and does not rely on a prior segmentation into semantic components. The method is based on a novel data structure for fast retrieval of partial matches: the randomized compound k‐NN graph built on multi‐view shape projections. We also employ a coarse‐to‐fine strategy to progressively refine part boundaries down to the level of individual faces. Experimental results indicate that our approach provides an intuitive and easy means to extract customized parts from a shape database, and significantly expands the design space for the user. We demonstrate several applications of our method to shape design and exploration.     

Scalable protection for MPEG-4 fine granularity scalability

The newly adopted MPEG-4 fine granularity scalability (FGS) video coding standard offers easy and flexible adaptation to varying network bandwidths and different application needs. Encryption for FGS should preserve such adaptation capabilities and enable intermediate stages to process encrypted data directly without decryption. In this paper, we propose two novel encryption algorithms for MPEG-4 FGS that meet these requirements. The first algorithm encrypts an FGS stream (containing both the base and the enhancement layers) into a single access layer and preserves the original fine granularity scalability and error resilience performance in an encrypted stream. The second algorithm encrypts an FGS stream into multiple quality layers divided according to either peak signal-to-noise ratio (PSNR) or bit rates, with lower quality layers being accessible and reusable by a higher quality layer of the same type, but not vice versa. Both PSNR and bit-rate layers are supported simultaneously so a layer of either type can be selected on the fly without decryption. The base layer for the second algorithm may be unencrypted to allow free view of the content at low-quality or content-based search of a video database without decryption. Both algorithms are fast, error-resilient, and have negligible compression overhead. The same approach can be applied to other scalable multimedia formats.     

改进的快速虹膜定位算法

针对虹膜的灰度分布特点,提出了一种粗定位和精定位相结合的虹膜定位算法。首先,通过k-mans聚类算法对图像进行动态阈值分割,分离出瞳孔区域,利用圆的几何特性进行粗定位;然后运用Gauss滤波降低噪声干扰和Canny算子进行边缘检测,结合粗定位的结果,应用Hough变换进行精定位,以快速提取虹膜内外边缘。实验表明,该方法能准确快速地定位虹膜的边界以满足实时性要求。     

测量用视觉传感器的自动聚焦

研究了一种新型测量用视觉传感器自动聚焦的实现,采用灰度变化率之和清晰度评价函数对被测物体进行大范围的粗聚焦,利用Roberts梯度函数实现在峰值附近的精确聚焦,并由计算机串口发控制命令驱动电机转动镜头至对焦清楚的位置。该系统具有简单实用、可靠等优点。仿真实验结果表明:自动聚焦的效果具有很好的准确度,能够满足系统的要求。     

利用众包更新Wi-Fi室内定位指纹库的方法研究

Wi-Fi定位是目前较为主流的室内定位方法,而位置指纹库的建立和维护对Wi-Fi定位至关重要。Wi-Fi信号时变性强要求指纹库及时更新。针对由专业人员更新指纹库的人力耗费问题,提出利用众包更新指纹库的方法,允许用户对定位结果进行评价和修正,使得用户在享受定位结果的同时参与到指纹库的维护更新中,特别针对用户的错误修正提出了基于聚类的错误检测方法,能有效避免指纹库被错误指纹污染。开发了室内定位系统,通过在真实室内环境的实验验证了本文提出的方法可以长时间保持较高的定位性能。     

Multi-database exploration of large design spaces in the framework of cascade evolutionary structural sizing optimization

In discrete sizing optimization of truss and frame structures the design variables take values from databases, which are usually populated with a relatively small number of cross-section types and sizes. The aim of this work is to allow the use of large-size databases in discrete structural sizing optimization problems, in order to enrich the set of design variable options and increase the potential of achieving high-quality optimal designs. For this purpose, the concept of coarse database is introduced, according to which smaller-size versions of an appropriately ordered large database can be constructed. This concept is combined with the idea of cascading, which allows a single optimization problem to be tackled with a number of autonomous optimization stages. Under this context, several coarse versions of the same full-size database are formed, in order to utilize a different database in each cascade stage executed with an evolutionary optimization algorithm. The first optimization stages of the resulting multi-database cascade procedure make use of the coarsest database versions available and serve the purpose of basic design space exploration. The last stages exploit finer databases (including the original full-size database) and aim in fine tuning the achieved optimal solution. Based on the reported numerical results, multi-database cascading proves to be an effective tool for the handling of large databases and corresponding extensive design spaces in the framework of discrete structural sizing optimization applications.     

绝对式圆感应同步器粗精数据融合

为了在测角系统中获得绝对角度,需要对绝对式圆感应同步器的粗通道和精通道数据进行融合.提出了一种粗精数据融合方法,具体阐述了粗通道的角度补偿和精通道的周期修正,相对于传统的不对粗通道进行补偿的方式,该方法可以使得测角系统适应更加恶劣的环境,拥有更高的可靠性,试验结果表明,数据融合算法正确可靠,在高低温真空条件下仍然可以获得准确的绝对角度.     

基于循环显著性校准网络的胰腺分割方法

胰腺的准确分割对于胰腺癌的识别和分析至关重要. 研究者提出通过第一阶段粗分割掩码的位置信息缩小第二阶段细分割网络输入的由粗到细分割方法, 尽管极大地提升了分割精度, 但是在胰腺分割过程中对于上下文信息的利用却存在以下两个问题: 1) 粗分割和细分割阶段分开训练, 细分割阶段缺少粗分割阶段分割掩码信息, 抑制了阶段间上下文信息的流动, 导致部分细分割阶段结果无法比粗分割阶段更准确; 2) 粗分割和细分割阶段单批次相邻预测分割掩码之间缺少信息互监督, 丢失切片上下文信息, 增加了误分割风险. 针对上述问题, 提出了一种基于循环显著性校准网络的胰腺分割方法. 通过循环使用前一阶段输出的胰腺分割掩码作为当前阶段输入的空间权重, 进行两阶段联合训练, 实现阶段间上下文信息的有效利用; 提出卷积自注意力校准模块进行胰腺预测分割掩码切片上下文信息跨顺序互监督, 显著改善了相邻切片误分割现象. 提出的方法在公开的数据集上进行了验证, 实验结果表明其改善误分割结果的同时提升了平均分割精度.     

Multiscale video sequence matching for near-duplicate detection and retrieval

As one of key technologies in content-based near-duplicate detection and video retrieval, video sequence matching can be used to judge whether two videos exist duplicate or near-duplicate segments or not. Despite a lot of research efforts devoted in recent years, how to precisely and efficiently perform sequence matching among videos (which may be subject to complex audio-visual transformations) from a large-scale database still remains a pretty challenging task. To address this problem, this paper proposes a multiscale video sequence matching (MS-VSM) method, which can gradually detect and locate the similar segments between videos from coarse to fine scales. At the coarse scale, it makes use of the Maximum Weight Matching (MWM) algorithm to rapidly select several candidate reference videos from the database for a given query. Then for each candidate video, its most similar segment with respect to the given query is obtained at the middle scale by the Constrained Longest Ascending Matching Subsequence (CLAMS) algorithm, and then can be used to judge whether that candidate exists near-duplicate or not. If so, the precise locations of the near-duplicate segments in both query and reference videos are determined at the fine scale by using bi-directional scanning to check the matching similarity at the segments’ boundaries. As such, the MS-VSM method can achieve excellent near-duplicate detection accuracy and localization precision with a very high processing efficiency. Extensive experiments show that it outperforms several state-of-the-art methods remarkably on several benchmarks.