Jean-Philippe Pernot

3D sketching with fully free form deformation features (δ-F 4 ) for aesthetic design

This paper addresses the designers activity and in particular the way designers express an object shape in 2D sketches through character lines. The tools currently available in commercial CAS/CAD systems to manipulate the digital models are still not sufficiently suited to support design. In this paper, we introduce the so-called Fully Free Form Deformation Features (δ-F4), able to take into account the curve-oriented stylists way of working. Both the advantages of a free form surfaces deformation method and a feature-based approach are merged to define highlevel modelling entities allowing for a direct manipulation of surfaces through a restricted number of intuitive parameters. In addition, a δ-F4 classification is proposed to permit a fast access to the desired shape according to its semantics. The proposed approach is illustrated with some examples.

Parameterised free-form feature templates

Even if todays CAD systems can easily represent free-form shapes by means of NURBS surfaces, their definition and modification still require a deep knowledge and a great skill in the manipulation of the underlying mathematical models. This paper presents an attempt to bring the feature concepts, well-known in the classical mechanical domain, to the free-form domain. The paper extends our previous work on fully free-form features to include parameterised feature templates. The free-form shapes are obtained by deformation according to specific constraint lines taking part to the feature templates definition. The feature template is adapted to the user-specified parameter values by our deformation engine, which can applied either to surfaces and curves. The method is illustrated with examples obtained with our prototype software.

Multi-minimisations for shape control of fully free-form deformation features (/spl delta/-F/sup 4/)

Fully free form deformation features (/spl delta/-F/sup 4/) have been proposed to overcome the limits of low-level manipulations of free form surfaces. They correspond to shapes obtained by deformation of a surface part according to geometric constraints. In our approach, a /spl delta/-F/sup 4/ is a result of the indirect manipulation of external forces applied to the nodes of a bar network coupled to the control polyhedron of a B-spline surface. The solution of the equation system corresponding to the constraint specifications, often under-constrained, requires the definition of an optimisation problem where an additional objective function has to be minimised. In this paper, we propose a new formulation of this optimisation problem where the proposed objective functions can be defined as a multiple combination of various local quantities. They can be related either to the geometry of the bar network (e.g. the length of a bar or the displacement of a node), or to its mechanical magnitudes (e.g. the external force applied at a node or a bar deformation energy). Different types of combinations are also proposed and classified according to the induced level of multi-minimisations. In this way, the shape of a /spl delta/-F/sup 4/ can be controlled globally, with a unique minimisation, or locally with different minimisations applied to sub-domains of the surface.

Polyhedral simplification preserving character lines extracted from images

Visualisation, assembling/disassembling simulation, reverse engineering, or finite element analyses are so many applications where a polyhedral simplification can be mandatory. In most of the configurations, such an operation must preserve the significant shapes of the original model. This paper addresses the way these simplifications can be performed while preserving character lines, i.e. those lines which affect significantly the object visual appearance. The proposed simplification process is based on a vertex removal algorithm that uses a heterogeneous map of sizes computed with information extracted from 2D images of the object. The farther the vertices are from the character lines, the more the simplification is important. The geodesic distances are estimated while using a new algorithm based on the analysis of multiple filtering of the images. This method might reduce the computational time since there is no need to compute either the curvature or the saliency. Thus, a first attempt to enrich a polyhedral model with semantic information extracted from images is proposed.