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78
iWIRES: An analyzeandedit approach to shape manipulation
 ACM SIGGRAPH Trans. Graph
, 2009
"... Figure 1: A complex model (left) consisting of 108 components is analyzed and 250 intelligent wires (in green) are extracted. Editing a few wires induces a new wire configuration (in blue) and leads to the result on the right. Manmade objects are largely dominated by a few typical features that car ..."
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Cited by 50 (16 self)
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Figure 1: A complex model (left) consisting of 108 components is analyzed and 250 intelligent wires (in green) are extracted. Editing a few wires induces a new wire configuration (in blue) and leads to the result on the right. Manmade objects are largely dominated by a few typical features that carry special characteristics and engineered meanings. Stateoftheart deformation tools fall short at preserving such characteristic features and global structure. We introduce iWIRES, a novel approach based on the argument that manmade models can be distilled using a few special 1D wires and their mutual relations. We hypothesize that maintaining the properties of such a small number of wires allows preserving the defining characteristics of the entire object. We introduce an analyzeandedit approach, where prior to editing, we perform a lightweight analysis of the input shape to extract a descriptive set of wires. Analyzing the individual and mutual properties of the wires, and augmenting them with geometric attributes makes them intelligent and ready to be manipulated. Editing the object by modifying the intelligent wires leads to a powerful editing framework that retains the original design intent and object characteristics. We show numerous results of manipulation of manmade shapes using our editing technique.
Partial intrinsic reflectional symmetry of 3d shapes
 ACM Transactions on Graphics (TOG
"... Figure 1: Given a closed 2manifold mesh, we compute a scalar field (a), which accentuates the axes of prominent, partial intrinsic reflectional symmetries. The top few (closed) Voronoi boundaries (b) between symmetric point pairs, as induced by the scalar field, can be imperfect. We develop an iter ..."
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Cited by 22 (3 self)
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Figure 1: Given a closed 2manifold mesh, we compute a scalar field (a), which accentuates the axes of prominent, partial intrinsic reflectional symmetries. The top few (closed) Voronoi boundaries (b) between symmetric point pairs, as induced by the scalar field, can be imperfect. We develop an iterative refinement scheme to extract the final set of intrinsic reflectional symmetry axes or IRSAs (c), which can be open curves. Incorporating symmetry cues offered by IRSAs into a conventional mesh segmentation scheme leads to highly semantic results (d). While many 3D objects exhibit various forms of global symmetries, prominent intrinsic symmetries which exist only on parts of an object are also well recognized. Such partial symmetries are often seen as more natural than a global one, even when the symmetric parts are under complex pose. We introduce an algorithm to extract partial intrinsic reflectional symmetries (PIRS) of a 3D shape. Given a closed 2manifold mesh, we develop a voting scheme to obtain an intrinsic reflectional symmetry axis (IRSA) transform, which is a scalar field over the mesh that accentuates prominent IRSAs of the shape. We then extract a set of explicit IRSA curves on the shape based on a refined measure of local reflectional symmetry support along a curve. The iterative refinement procedure combines IRSAinduced region growing and regionconstrained symmetry support refinement to improve accuracy and address potential issues arising from rotational symmetries in the shape. We show how the extracted IRSA curves can be incorporated into a conventional mesh segmentation scheme so that the implied symmetry cues can be utilized to obtain more meaningful results. We also demonstrate the use of IRSA curves for symmetrydriven part repair. 1
Nonlocal Scan Consolidation for 3D Urban Scenes
"... Recent advances in scanning technologies, in particular devices that extract depth through active sensing, allow fast scanning of urban scenes. Such rapid acquisition incurs imperfections: large regions remain missing, significant variation in sampling density is common, and the data is often corrup ..."
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Cited by 20 (7 self)
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Recent advances in scanning technologies, in particular devices that extract depth through active sensing, allow fast scanning of urban scenes. Such rapid acquisition incurs imperfections: large regions remain missing, significant variation in sampling density is common, and the data is often corrupted with noise and outliers. However, buildings often exhibit large scale repetitions and selfsimilarities. Detecting, extracting, and utilizing such large scale repetitions provide powerful means to consolidate the imperfect data. Our key observation is that the same geometry, when scanned multiple times over reoccurrences of instances, allow application of a simple yet effective nonlocal filtering. The multiplicity of the geometry is fused together and projected to a basegeometry defined by clustering corresponding surfaces. Denoising is applied by separating the process into offplane and inplane phases. We show that the consolidation of the reoccurrences provides robust denoising and allow reliable completion of missing parts. We present evaluation results of the algorithm on several LiDAR scans of buildings of varying complexity and styles. 1
Symmetry factored embedding and distance
 ACM Trans. Graph. (Proc. SIGGRAPH
, 2010
"... We introduce the Symmetry Factored Embedding (SFE) and the Symmetry Factored Distance (SFD) as new tools to analyze and represent symmetries in a point set. The SFE provides new coordinates in which symmetry is “factored out, ” and the SFD is the Euclidean distance in that space. These constructions ..."
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Cited by 20 (4 self)
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We introduce the Symmetry Factored Embedding (SFE) and the Symmetry Factored Distance (SFD) as new tools to analyze and represent symmetries in a point set. The SFE provides new coordinates in which symmetry is “factored out, ” and the SFD is the Euclidean distance in that space. These constructions characterize the space of symmetric correspondences between points – i.e., orbits. A key observation is that a set of points in the same orbit appears as a clique in a correspondence graph induced by pairwise similarities. As a result, the problem of finding approximate and partial symmetries in a point set reduces to the problem of measuring connectedness in the correspondence graph, a wellstudied problem for which spectral methods provide a robust solution. We provide methods for computing the SFE and SFD for extrinsic global symmetries and then extend them to consider partial extrinsic and intrinsic cases. During experiments with difficult examples, we find that the proposed methods can characterize symmetries in inputs with noise, missing data, nonrigid deformations, and complex symmetries, without a priori knowledge of the symmetry group. As such, we believe that it provides a useful tool for automatic shape analysis in applications such as segmentation and stationary point detection. 1
SmartBoxes for Interactive Urban Reconstruction
"... We introduce an interactive tool which enables a user to quickly assemble an architectural model directly over a 3D point cloud acquired from largescale scanning of an urban scene. The user loosely defines and manipulates simple building blocks, which we call SmartBoxes, over the point samples. T ..."
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Cited by 17 (1 self)
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We introduce an interactive tool which enables a user to quickly assemble an architectural model directly over a 3D point cloud acquired from largescale scanning of an urban scene. The user loosely defines and manipulates simple building blocks, which we call SmartBoxes, over the point samples. These boxes quickly snap to their proper locations to conform to common architectural structures. The key idea is that the building blocks are smart in the sense that their locations and sizes are automatically adjusted onthefly to fit well to the point data, while at the same time respecting contextual relations with nearby similar blocks. SmartBoxes are assembled through a discrete optimization to balance between two snapping forces defined respectively by a datafitting term and a contextual term, which together assist the user in reconstructing the architectural model from a sparse and noisy point cloud. We show that a combination of the user’s interactive guidance and highlevel knowledge about the semantics of the underlying model, together with the snapping forces, allows the reconstruction of structures which are partially or even completely missing from the input.
Completion and Reconstruction with Primitive Shapes
 Computer Graphics Forum (Proc. of Eurographics
, 2009
"... Figure 1: Reconstruction of the fandisk model. Orange color signifies completed surface parts. (a) The input pointcloud with holes (b) Final result (c) Result without the connectivity enforcement algorithm of Sec. 5. The disconnected primitive highlighted in red cuts off part of the model. (d) Clos ..."
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Cited by 17 (0 self)
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Figure 1: Reconstruction of the fandisk model. Orange color signifies completed surface parts. (a) The input pointcloud with holes (b) Final result (c) Result without the connectivity enforcement algorithm of Sec. 5. The disconnected primitive highlighted in red cuts off part of the model. (d) Closeup views of result without consistent edge labels and final result (see Sec. 7) We consider the problem of reconstruction from incomplete pointclouds. To find a closed mesh the reconstruction is guided by a set of primitive shapes which has been detected on the input pointcloud (e.g. planes, cylinders etc.). With this guidance we not only continue the surrounding structure into the holes but also synthesize plausible edges and corners from the primitives ’ intersections. To this end we give a surface energy functional that incorporates the primitive shapes in a guiding vector field. The discretized functional can be minimized with an efficient graphcut algorithm. A novel greedy optimization strategy is proposed to minimize the functional under the constraint that surface parts corresponding to a given primitive must be connected. From the primitive shapes our method can also reconstruct an idealized model that is suitable for use in a CAD system. Categories and Subject Descriptors (according to ACM CCS): Computer Graphics [I.3.5]: Curve, surface, solid, and object representations— 1.
StyleContent Separation by Anisotropic Part Scales
"... We perform coanalysis of a set of manmade 3D objects to allow the creation of novel instances derived from the set. We analyze the objects at the part level and treat the anisotropic part scales as a shape style. The coanalysis then allows style transfer to synthesize new objects. The key to coa ..."
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Cited by 16 (11 self)
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We perform coanalysis of a set of manmade 3D objects to allow the creation of novel instances derived from the set. We analyze the objects at the part level and treat the anisotropic part scales as a shape style. The coanalysis then allows style transfer to synthesize new objects. The key to coanalysis is part correspondence, where a major challenge is the handling of large style variations and diverse geometric content in the shape set. We propose stylecontent separation as a means to address this challenge. Specifically, we define a correspondencefree style signature for style clustering. We show that confining analysis to within a style cluster facilitates tasks such as cosegmentation, content classification, and deformationdriven part correspondence. With part correspondence between each pair of shapes in the set, style transfer can be easily performed. We demonstrate our analysis and synthesis results on several sets of manmade objects with style and content variations.
Paneling Architectural Freeform Surfaces
"... The emergence of largescale freeform shapes in architecture poses big challenges to the fabrication of such structures. A key problem is the approximation of the design surface by a union of patches, socalled panels, that can be manufactured with a selected technology at reasonable cost, while meet ..."
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Cited by 15 (8 self)
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The emergence of largescale freeform shapes in architecture poses big challenges to the fabrication of such structures. A key problem is the approximation of the design surface by a union of patches, socalled panels, that can be manufactured with a selected technology at reasonable cost, while meeting the design intent and achieving the desired aesthetic quality of panel layout and surface smoothness. The production of curved panels is mostly based on molds. Since the cost of mold fabrication often dominates the panel cost, there is strong incentive to use the same mold for multiple panels. We cast the major practical requirements for architectural surface paneling, including mold reuse, into a global optimization framework that interleaves discrete and continuous optimization steps to minimize production cost while meeting userspecified quality constraints. The search space for optimization is mainly generated through controlled deviation from the design surface and tolerances on positional and normal continuity between neighboring panels. A novel 6dimensional metric space allows us to quickly compute approximate interpanel distances, which dramatically improves the performance of the optimization and enables the handling of complex arrangements with thousands of panels. The practical relevance of our system is demonstrated by paneling solutions for real, cuttingedge architectural freeform design projects.
RepFinder: Finding Approximately Repeated Scene Elements for Image Editing
"... Figure 1: Repeated element detection and manipulation. (Lefttoright) Original image with user scribbles to indicate an object template (red) and background (green); repeated instances detected, completed, dense correspondence established, and ordered in layers; fish in the original image replaced ..."
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Cited by 14 (9 self)
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Figure 1: Repeated element detection and manipulation. (Lefttoright) Original image with user scribbles to indicate an object template (red) and background (green); repeated instances detected, completed, dense correspondence established, and ordered in layers; fish in the original image replaced by a different kind of fish from a reference image (topright inset); rearranged fishes. Repeated elements are ubiquitous and abundant in both manmade and natural scenes. Editing such images while preserving the repetitions and their relations is nontrivial due to overlap, missing parts, deformation across instances, illumination variation, etc. Manually enforcing such relations is laborious and errorprone. We propose a novel framework where user scribbles are used to guide detection and extraction of such repeated elements. Our detection process, which is based on a novel boundary band method, robustly extracts the repetitions along with their deformations. The algorithm only considers the shape of the elements, and ignores similarity based on color, texture, etc. We then use topological sorting to establish a partial depth ordering of overlapping repeated instances. Missing parts on occluded instances are completed using information from other instances. The extracted repeated instances can then be seamlessly edited and manipulated for a variety of high level tasks that are otherwise difficult to perform. We demonstrate the versatility of our framework on a large set of inputs of varying complexity, showing applications to image rearrangement, edit transfer, deformation propagation, and instance replacement. image editing, shapeaware manipulation, edit propaKeywords: gation
Robust Voronoibased Curvature and Feature Estimation
 SIAM/ACM JOINT CONFERENCE ON GEOMETRIC AND PHYSICAL MODELING
, 2009
"... Many algorithms for shape analysis and shape processing rely on accurate estimates of di erential information such as normals and curvature. In most settings, however, care must be taken around nonsmooth areas of the shape where these quantities are not easily de ned. This problem is particularly pr ..."
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Cited by 12 (2 self)
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Many algorithms for shape analysis and shape processing rely on accurate estimates of di erential information such as normals and curvature. In most settings, however, care must be taken around nonsmooth areas of the shape where these quantities are not easily de ned. This problem is particularly prominent with pointcloud data, which are discontinuous everywhere. In this paper we present an e cient and robust method for extracting principal curvatures, sharp features and normal directions of a piecewise smooth surface from its point cloud sampling, with theoretical guarantees. Our method is integral in nature and uses convolved covariance matrices of Voronoi cells of the point cloud which makes it provably robust in the presence of noise. We show analytically that our method recovers correct principal curvatures and principal curvature directions in smooth parts of the shape, and correct feature directions and feature angles at the sharp edges of a piecewise smooth surface, with the error bounded by the Hausdor distance between the point cloud and the underlying surface. Using the same analysis we provide theoretical guarantees for a modi cation of a previously proposed normal estimation technique. We illustrate the correctness of both principal curvature information and feature extraction in the presence of varying levels of noise and sampling density on a variety of models.