Topological Errors Research Articles

A method for verification of computer-aided design model errors

Computer-aided design (CAD) models have errors that originate from data loss during the data conversion process or the technical weakness of the neutral format. Error recovery requires an increase in lead-time and additional expenses for product development. The serious problem is that errors in a CAD model are not found until after downstream development processes. In this paper, we propose a method to identify CAD model errors that are contained in a neutral format. Considering different topological and geometrical characteristics in the exchange of product model data (STEP) and initial graphics exchange specification (IGES) formats, our method includes a verification process to check a CAD model error step by step without wasting resources. To test the idea, we have implemented a verification system that checks topological and geometrical errors of 19 items in the STEP format and 12 items in the IGES format.

Physics-based protein-structure prediction using a hierarchical protocol based on the UNRES force field: Assessment in two blind tests

Recent improvements in the protein-structure prediction method developed in our laboratory, based on the thermodynamic hypothesis, are described. The conformational space is searched extensively at the united-residue level by using our physics-based UNRES energy function and the conformational space annealing method of global optimization. The lowest-energy coarse-grained structures are then converted to an all-atom representation and energy-minimized with the ECEPP/3 force field. The procedure was assessed in two recent blind tests of protein-structure prediction. During the first blind test, we predicted large fragments of alpha and alpha+beta proteins [60-70 residues with C(alpha) rms deviation (rmsd) <6 A]. However, for alpha+beta proteins, significant topological errors occurred despite low rmsd values. In the second exercise, we predicted whole structures of five proteins (two alpha and three alpha+beta, with sizes of 53-235 residues) with remarkably good accuracy. In particular, for the genomic target TM0487 (a 102-residue alpha+beta protein from Thermotoga maritima), we predicted the complete, topologically correct structure with 7.3-A C(alpha) rmsd. So far this protein is the largest alpha+beta protein predicted based solely on the amino acid sequence and a physics-based potential-energy function and search procedure. For target T0198, a phosphate transport system regulator PhoU from T. maritima (a 235-residue mainly alpha-helical protein), we predicted the topology of the whole six-helix bundle correctly within 8 A rmsd, except the 32 C-terminal residues, most of which form a beta-hairpin. These and other examples described in this work demonstrate significant progress in physics-based protein-structure prediction.

Including Ampere Measurements in Generalized State Estimators

Conventional state estimators (SEs) cannot take advantage of all available measurements, like currents flowing through circuit breakers and individual external injections. Current measurements are frequent at the lower voltage levels and their loss implies a reduction of the global redundancy and hence a deterioration of the SE filtering capability. In this paper, a methodology is presented allowing all current measurements to be included in the model. A generalized state estimator is used in which substations are compactly represented by means of an implicit model. To illustrate the performance of the proposed formulation, several simulations are presented. Results are validated by checking the accuracy of the estimated states and by showing the improved ability to detect and identify bad data and topology errors.

Identification of analog and topological measurement errors in generalized state estimation

This paper presents a method for analog and topological measurement error identification in generalized state estimation. Errors of analog measurements depend on measurement equipment accuracy. Errors of topological measurements (switching device statuses) result in erroneous network models. In generalized state estimation, analog and topological data are processed as a single interacting information set. The conventional measurement model is extended by incorporating the breaker statuses (open or closed) and the active and reactive power flows as continuous state variables. Depending on breaker statuses, additional pseudomeasurements are introduced. The method treats the analog and status measurements as regular measurements. Hypothesis testing for detection and identification of bad analog and topological measurements is used ( J ( x ˆ ) and r ˆ N , test respectively). Test results for the RTS substation system are reported.

Approximating centroids for the maximum intersection of spherical polygons

This paper considers the problem of investigating the spherical regions owned by the maximum number of spherical polygons. We present a practical O( n( v+ I)) time algorithm for finding the approximating centroids for the maximum intersection of spherical polygons, where n, v, and I are, respectively, the numbers of polygons, all vertices, and intersection points. In order to elude topological errors and handle geometric degeneracies, our algorithm takes the approach of edge-based partitioning of the sphere. Furthermore, the numerical complexity is avoided since the algorithm is completely spherical.

Shape-similarity search of 3D models by using enhanced shape functions

We propose a pair of shape features for searching surface-based 3D shape models based on their shape similarity. Either of the features is computed by first converting an input surface based model into an oriented point set model and then computing a joint 2D histogram of distance and orientation of pairs of points. Advantages of the shape features are: they can be computed for non-solid or non-manifold models; they are invariant to similarity transformation; and they are tolerant of topological and geometrical errors and degeneracies. Experiments showed that, with only a modest increase in computational cost, our shape features achieved significant performance improvement over Osada's D2, on which our features are based.

時点の異なる二つの領域分割図間から領域の変化を検出する一連の方法

This paper proposes methods for detecting the changes between spatial tessellations at two different points in time. First, we classify changes of sub-regions into categories and then mathematically formulate the detection of changes of sub-regions. Second, we eliminate systematic positional displacement. Third, we match sub-regions between two tessellations using a representative point of each sub-region. Fourth, we match boundaries between the tessellations and also detect topological errors. Fifth, we judge whether or not matched boundaries should be considered the same. Sixth, we detect the changes of sub-regions by eliminating matched boundaries which are considered different at the previous step. Last, we apply the proposed methods to the U.S. Census data, and conclude with future work.

A procedural approach of inspecting CAD model errors

Neutral format translators such as STEP and IGES have been used to exchange CAD model between the various CAD systems in the product development process. But imperfect interoperability imposes costs on the industry due to higher costs of design and production and slower implementation of design changes. In this paper, we propose a procedural approach to inspect the CAD model's errors that occur in a neutral format. We employed two separate inspection processes for checking CAD model errors without wasting excessive resources: the topological data structure and the geometrical data structure. We developed the 3D CAD model inspection system to check the topological and geometrical errors and applied it to case study. An inspection record can be edited in HTML, and thus can be shared by any designer at any time.

An algebraic approach to practical and scalable overlay network monitoring

Overlay network monitoring enables distributed Internet applications to detect and recover from path outages and periods of degraded performance within seconds. For an overlay network with n end hosts, existing systems either require O ( n 2 ) measurements, and thus lack scalability, or can only estimate the latency but not congestion or failures. Our earlier extended abstract [1] briefly proposes an algebraic approach that selectively monitors k linearly independent paths that can fully describe all the O ( n 2 ) paths. The loss rates and latency of these k paths can be used to estimate the loss rates and latency of all other paths. Our scheme only assumes knowledge of the underlying IP topology, with links dynamically varying between lossy and normal.In this paper, we improve, implement and extensively evaluate such a monitoring system. We further make the following contributions: i) scalability analysis indicating that for reasonably large n ( e.g. , 100), the growth of k is bounded as O ( n log n ), ii) efficient adaptation algorithms for topology changes, such as the addition or removal of end hosts and routing changes, iii) measurement load balancing schemes, and iv) topology measurement error handling. Both simulation and Internet experiments demonstrate we obtain highly accurate path loss rate estimation while adapting to topology changes within seconds and handling topology errors.

Interactive 3D segmentation using connected orthogonal contours

This paper describes a new method for interactive segmentation that is based on cross-sectional design and 3D modelling. The method represents a 3D model by a set of connected contours that are planar and orthogonal. Planar contours overlayed on image data are easily manipulated and linked contours reduce the amount of user interaction.1 This method solves the contour–to–contour correspondence problem and can capture extrema of objects in a more flexible way than manual segmentation of a stack of 2D images. The resulting 3D model is guaranteed to be free of geometric and topological errors. We show that manual segmentation using connected orthogonal contours has great advantages over conventional manual segmentation. Furthermore, the method provides effective feedback and control for creating an initial model for, and control and steering of, (semi-)automatic segmentation methods.

Bayesian-Based Hypothesis Testing for Topology Error Identification in Generalized State Estimation

This paper develops a Bayesian-based hypothesis testing procedure to be applied in conjunction with topology error processing via normalized Lagrange multipliers. As an advantage over previous methods, the proposed approach eliminates the need of repeated state estimator runs for alternative hypothesis evaluation. The identification process assumes that the set of switching devices is partitioned into suspect and true subsets. A geometric test is devised to ensure that all devices with wrong status are included in the suspect set. In addition, the results of criticality analysis performed at substation physical level prevents the occurrence of matrix singularities, which otherwise would degrade the performance of topology error identification. The IEEE 24-bus test system represented at physical level is employed to evaluate the proposed approach, considering diverse substation layouts and distinct types of topology errors.

Interactive 3D segmentation using connected orthogonal contours

This paper describes a new method for interactive segmentation that is based on cross-sectional design and 3D modelling. The method represents a 3D model by a set of connected contours that are planar and orthogonal. Planar contours overlayed on image data are easily manipulated and linked contours reduce the amount of user interaction.1 This method solves the contour–to–contour correspondence problem and can capture extrema of objects in a more flexible way than manual segmentation of a stack of 2D images. The resulting 3D model is guaranteed to be free of geometric and topological errors. We show that manual segmentation using connected orthogonal contours has great advantages over conventional manual segmentation. Furthermore, the method provides effective feedback and control for creating an initial model for, and control and steering of, (semi-)automatic segmentation methods.

Removing excess topology from isosurfaces

Many high-resolution surfaces are created through isosurface extraction from volumetric representations, obtained by 3D photography, CT, or MRI. Noise inherent in the acquisition process can lead to geometrical and topological errors. Reducing geometrical errors during reconstruction is well studied. However, isosurfaces often contain many topological errors in the form of tiny handles. These nearly invisible artifacts hinder subsequent operations like mesh simplification, remeshing, and parametrization. In this article we present a practical method for removing handles in an isosurface. Our algorithm makes an axis-aligned sweep through the volume to locate handles, compute their sizes, and selectively remove them. The algorithm is designed to facilitate out-of-core execution. It finds the handles by incrementally constructing and analyzing a Reeb graph. The size of a handle is measured by a short nonseparating cycle. Handles are removed robustly by modifying the volume rather than attempting "mesh surgery." Finally, the volumetric modifications are spatially localized to preserve geometrical detail. We demonstrate topology simplification on several complex models, and show its benefits for subsequent surface processing.

Matching of 3D tree structures using association graphs

AbstractMatching of tree structures is equivalent to the problem of searching for maximum cliques in tree association graphs. Pelillo and colleagues have recently proposed a method for searching for maximum weight cliques that gives weight to association graphs on the basis of similarities of the attributes of tree nodes. Here, the obtained maximum weight clique corresponds to the maximum similarity subtree isomorphism. This paper proposes a tree structure‐matching scheme using tree association graphs, as a general scheme for performing nonrigid body registration of tree structures in three‐dimensional medical images. Matching of tree structures of three‐dimensional medical images of bronchi, blood vessels, and the like must be capable of handling changes in body positions accompanying their changes as well as physiological changes due to breathing exercises etc. In addition, it needs to recognize topology errors of pseudo or false branches occurring during image processing. This study, as attributes of tree nodes, constructs similarities using body volume change rates extending over the parents, children and siblings, focusing on the positional relations of the nodes of the parents, children, and siblings. The similarities proposed are those having high general properties that can be applied to changes in positions and shapes that occur inside a body since they focus on their general properties. In addition, as a method for avoiding mismatches due to topology errors, changing the weights of neighboring edges on the basis of similarities is added. The proposed scheme has been confirmed to show a high correct solution rate or true positive fraction regardless of high degree changes in positions and shapes when applied to a bronchial model generated inside a computer. It has also been confirmed that mismatches due to topology errors occur at a very low rate with the proposed scheme. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(2): 59–72, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10216

Approximating Centroids for the Maximum Intersection of Spherical Polygons

AbstractThis paper considers the problem of investigating the spherical regions owned by the maximum number of spherical polygons. We present a practical O(n(v+I)) time algorithm for finding the approximating centroids for the maximum intersection of spherical polygons, where n, v, and I are, respectively, the numbers of polygons, all vertices, and intersection points. In order to elude topological errors and handle geometric degeneracies, our algorithm takes the approach of edge-based partitioning of the sphere. Furthermore, the numerical complexity is avoided since the algorithm is completely spherical.

Identificação de erros de topologia via multiplicadores de Lagrange normalizados e testes de hipóteses

Este artigo desenvolve uma metodologia baseada em testes de hipóteses a ser associada à técnica de identificação de erros topológicos via multiplicadores de Lagrange normalizados recentemente proposta na literatura. O principal objetivo é eliminar a necessidade de re-estimação de estados a cada nova configuração a ser testada, requerida pelo método citado. As hipóteses são definidas pelos status dos disjuntores suspeitos de terem sido erroneamente modelados. Os testes de hipóteses propostos aplicam o teorema de Bayes de modo a obter como resultado probabilidades condicionais para as hipóteses. A partir destas, é possível identificar a correta configuração da rede.

The effects of increasing genetic distance on alignment of, and tree construction from, rDNA internal transcribed spacer sequences

We examined how alignment of internal transcribed spacers of rDNA in fungi and plants changes with increasing genetic distance by successive removal of sequences from each data set followed by realignment and phylogenetic analysis. Increasing genetic distance can negatively affect phylogenetic reconstruction in two ways. First, it may cause errors in the alignment and therefore the homology hypotheses of the sequence characters. Second, it may cause errors in the homology assessments of character states because of multiple hits on individual branches. These two causes of error in phylogenetic inference were distinguished from one another in our analysis. The errors in alignment caused by increasing genetic distance were primarily due to inserting too few gaps and inserting gaps at the wrong positions. Errors in tree resolution, topology, and/or branch-support values were more often caused by multiple hits than by misaligned positions. This suggests that increasing genetic distance negatively affects our primary homology assessments of character states more severely than our primary homology assessments of characters. We suggest that increasing taxon sampling with the aim of subdividing long branches is a strategy for obtaining reliable alignments.

A front tracking method on unstructured grids

A numerical method is developed for tracking discontinuities which is integrated in a generalized finite-volume solution framework for systems of conservation laws on unstructured grids of arbitrary element type. The location, geometry and the movement of the discontinuities are described by a local level set method on a restricted, dynamic definition range. Special algorithms based on least square methods are developed for handling the transport and renormalization of the level set function within the restricted range. An additional error correction is employed to minimize topological errors of the tracked front geometry. The jump conditions at the front are updated by one-sided extrapolation which define the local front velocity and the Riemann problem. A flux separation concept enables the treatment of the discontinuity within the finite-volume concept. The front tracking method is demonstrated by a number of computational examples for shock wave problems.

Extension of surface reconstruction algorithm to the global stitching and repairing of STL models

In the design of complex parts involving free-form or sculptured surfaces, the design is usually represented by a B-rep model. But in production involving rapid prototyping (RP) or solid machining, the B-rep model is often converted to the popular STL model. Due to defects such as topological and geometric errors in the B-rep model, the resulting STL model may contain gaps, overlaps, and inconsistent orientations. This paper presents the extension of a surface reconstruction algorithm to the global stitching of STL models for RP and solid machining applications. The model to be stitched may come from the digitization of physical objects by 3D laser scanners, or the triangulation of trimmed surfaces of a B-rep model. Systematic procedures have been developed for each of these two different but equally important cases. The result shows that the proposed method can robustly and effectively solve the global stitching problem for very complex STL models.

Dynamic-state-estimation scheme including nonlinear measurement function considerations

An algorithm that includes nonlinear measurement-function considerations is proposed. To enhance the robustness of the method, the exponential weight function was embedded and the nonlinear measurement function was integrated with the state-estimation model. In this way, the method can be employed in different scenarios while the estimation performance can be maintained effectively. This approach has been tested on different power systems under various operating conditions, where normal operation, bad measurement, sudden load change and topology error are all investigated. The performance indices under different test cases were also evaluated. Test results support the feasibility of the proposed method for dynamic-state-estimation applications.