7 research outputs found
3D Mesh Simplification. A survey of algorithms and CAD model simplification tests
Simplification of highly detailed CAD models is an important step when CAD
models are visualized or by other means utilized in augmented reality applications.
Without simplification, CAD models may cause severe processing and storage is-
sues especially in mobile devices. In addition, simplified models may have other
advantages like better visual clarity or improved reliability when used for visual pose
tracking. The geometry of CAD models is invariably presented in form of a 3D
mesh. In this paper, we survey mesh simplification algorithms in general and focus
especially to algorithms that can be used to simplify CAD models. We test some
commonly known algorithms with real world CAD data and characterize some new
CAD related simplification algorithms that have not been surveyed in previous mesh
simplification reviews.Siirretty Doriast
A Constrained Resampling Strategy for Mesh Improvement
In many geometry processing applications, it is required to improve an initial mesh in terms of multiple quality objectives. Despite the availability of several mesh generation algorithms with provable guarantees, such generated meshes may only satisfy a subset of the objectives. The conflicting nature of such objectives makes it challenging to establish similar guarantees for each combination, e.g., angle bounds and vertex count. In this paper, we describe a versatile strategy for mesh improvement by interpreting quality objectives as spatial constraints on resampling and develop a toolbox of local operators to improve the mesh while preserving desirable properties. Our strategy judiciously combines smoothing and transformation techniques allowing increased flexibility to practically achieve multiple objectives simultaneously. We apply our strategy to both planar and surface meshes demonstrating how to simplify Delaunay meshes while preserving element quality, eliminate all obtuse angles in a complex mesh, and maximize the shortest edge length in a Voronoi tessellation far better than the state-of-the-art
Segmentation and Deformable Modelling Techniques for a Virtual Reality Surgical Simulator in Hepatic Oncology
Liver surgical resection is one of the most frequently used curative therapies. However,
resectability is problematic. There is a need for a computer-assisted surgical planning and
simulation system which can accurately and efficiently simulate the liver, vessels and
tumours in actual patients. The present project describes the development of these core
segmentation and deformable modelling techniques.
For precise detection of irregularly shaped areas with indistinct boundaries, the
segmentation incorporated active contours - gradient vector flow (GVF) snakes and level sets.
To improve efficiency, a chessboard distance transform was used to replace part of the GVF
effort. To automatically initialize the liver volume detection process, a rotating template was
introduced to locate the starting slice. For shape maintenance during the segmentation
process, a simplified object shape learning step was introduced to avoid occasional
significant errors. Skeletonization with fuzzy connectedness was used for vessel
segmentation.
To achieve real-time interactivity, the deformation regime of this system was based
on a single-organ mass-spring system (MSS), which introduced an on-the-fly local mesh
refinement to raise the deformation accuracy and the mesh control quality. This method was
now extended to a multiple soft-tissue constraint system, by supplementing it with an
adaptive constraint mesh generation. A mesh quality measure was tailored based on a wide
comparison of classic measures. Adjustable feature and parameter settings were thus
provided, to make tissues of interest distinct from adjacent structures, keeping the mesh
suitable for on-line topological transformation and deformation.
More than 20 actual patient CT and 2 magnetic resonance imaging (MRI) liver
datasets were tested to evaluate the performance of the segmentation method. Instrument
manipulations of probing, grasping, and simple cutting were successfully simulated on
deformable constraint liver tissue models. This project was implemented in conjunction with
the Division of Surgery, Hammersmith Hospital, London; the preliminary reality effect was
judged satisfactory by the consultant hepatic surgeon