Research Topics – Alla Sheffer
Published results can be downloaded (PDF) via publications list.
Recent Research Results (2003-present):
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Template-Based
Mesh Completion (with V. Kraevoy, SGP 05)
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Meshes generated by range scanners and other acquisition tools are often incomplete and typically contain multiple connected components with irregular boundaries and complex holes. This paper introduces a robust algorithm for completion of such meshes using a mapping between the incomplete mesh and a template model. The mapping is computed using a novel framework for bijective parameterization of meshes with gaps and holes. We employ this mapping to correctly glue together the components of the input mesh and to close the holes. The template is used to fill in the topological and geometric information missing in the input. As part of our completion method we propose a boundary-mapping technique useful for mesh editing operations such as merging, blending, and detail transfer. We demonstrate that by using this technique we can automatically perform complex editing operations that previously required a large amount of user interaction. |
D-Charts: Quasi-Developable
Mesh Segmentation
(with
D. Julius and V. Kraevoy, EG 05)
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Quasi-developable mesh
segmentation is necessary for many applications in graphics and CAD, including
texture atlas generation and the design of patterns for model fabrication
from sheets of material. In this work we introduce D-chars, a simple and
robust algorithm for mesh segmentation into (nearly) developable charts.
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Mesh Editing and Motion
Reconstruction from Mocup Data
(with V. Kraevoy)
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Geometry editing operations commonly use mesh encodings which capture the shape properties of the models. Given modified positions for a set of anchor vertices, the encoding is used to compute the positions for the rest of the mesh vertices, preserving the model shape as much as possible. In this work we introduce a new shape preserving and rotation invariant mesh encoding. We use this encoding for a variety of mesh editing applications: deformation, morphing, blending and motion reconstruction from Mocap data. The editing algorithms based on our encoding and decoding mechanism generate natural looking models that preserve the shape properties of the input. |
Cross-Parameterization &
Compatible Remeshing
(with V.
Kraevoy,
SIGGRAPH 2004) |
Many geometry processing applications, such as morphing, shape blending, transfer of texture or material properties, and fitting template meshes to scan data, require a bijective mapping between two or more models. This mapping, or cross-parameterization, typically needs to preserve the shape and features of the parameterized models, mapping legs to legs, ears to ears, and so on. Most of the applications also require the models to be represented by compatible meshes, i.e. meshes with identical connectivity, based on the cross-parameterization. We introduce novel methods for shape preserving cross-parameterization and compatible remeshing. Our cross-parameterization method computes a low-distortion bijective mapping between models that satisfies user prescribed constraints. Using this mapping, the remeshing algorithm preserves the user-defined feature vertex correspondence and the shape correlation between the models. The remeshing algorithm generates output meshes with significantly fewer elements compared to previous techniques, while accurately approximating the input geometry. |
Virtual Woodwork
(with
R. Raab & C.Gotsman)
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Shape idealization techniques provide a simplified description of a geometric model. Often idealized models are visually interesting and provide an appealing artistic impression of the models.We developed an algorithm for automatic generation of idealized bead figures from recognizable 3D models (animals, humans, etc…). The bead figures approximate the model by a set of cylindrical shapes threaded onto a skeleton of the model. The bead figures can be used by applications requiring a simple and compact description of the shapes. They also provide a visually appealing, toy-like description which can be used in artistic applications. In addition to the generation of the beaded figures our work also introduces a novel skeleton construction algorithm with several advantages over existing methods. |
Geodesic based surface remeshing
(with
O. Sifri & C.Gotsman,
IMR 2003) |
Generation of surface meshes remains an active research problem despite the many publications addressing this topic. The main issues which must be treated by a good remeshing algorithm are: element quality, sizing control, approximation accuracy, robustness and efficiency. One reason surface meshing is such a challenging problem is the fact that using the Euclidean metric to measure distances between points on the surface can generate large discrepancies between the original surface and the constructed mesh. We solve this problem by using geodesic distances on the surface. The ability to accurately and efficiently compute geodesic distances, and propagate them across the mesh, permits us to generate quality surface meshes which closely approximate the input without using costly parameterization techniques. |
Matchmaker: Constrained
parameterization with applications in texture mapping and morphing
(with
V. Kraevoy & C.Gotsman,
SIGGRAPH 2003) |
Adding constraints to 3D mesh parameterization in the plane is beneficial for many parameterization applications. One application we focused on is texture mapping. Texture mapping enhances the visual realism of 3D models by adding fine details. To achieve the best results, it is often necessary to force a correspondence between some of the details of the texture and the features of the model. The algorithm we work on forces feature correspondence for planar parameterization of meshes. This is achieved by adding positional constraints to the planar parameterization. The method allows users to introduce scores of constraints while maintaining a valid one-to-one mapping between the embedding and the 3D surface. |
Spherical Parameterization
(with C.Gotsman & X. Gu,
SIGGRAPH 2003)
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Closed manifold genus-0 meshes are
topologically equivalent to a sphere, hence this is the natural parameter
domain for them. Parameterizing a triangle mesh onto the sphere means
assigning a 3D position on the unit sphere to each of the mesh vertices, such
that the spherical triangles induced by the mesh connectivity do not overlap.
Satisfying the non-overlapping requirement is the most difficult and critical
component of this process. We developed a generalization of the method of
barycentric coordinates for planar parameterization which solves the
spherical parameterization problem. We prove its correctness by establishing
a connection to spectral graph theory and describe efficient numerical
methods for computing these parameterizations. New: Public domain fast implementation available at www.cs.technion.ac.il/~shadis |
As
part of our method we introduce a new metric of developability for mesh
surfaces. Thanks to this metric, using our segmentation for texture atlas
generation we are able to bound the distortion of the atlas directly during
the segmentation stage. We demonstrate that by using this bound we generate
more isometric atlases for the same number of charts compared to existing
state of the art techniques. Using our segmentation algorithm we also develop
a technique for automatic pattern design. To demonstrate the practicality
technique we use the patterns produced by our algorithm to make real fabric
and paper copies of popular computer graphics models.
The research topics I worked on in the past are divided into two lists:
1999-2002
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