Marc Neveu

Curvilinear displacement of free-form-based deformation

This paper presents an extension of a freeform deformation method. This method can be used on any object, whatever its geometrical description. It consists in fixing displacement constraint on an object and ensuring their satisfaction through the deformation. The final object is a blend of the deformation functions linked with the constraint. The user can also modify the extent of the constraints influences and the displacement of the constraint points to obtain a desired shape. This method keeps its initial properties and enables the deformation of the whole space.

Extended constrained deformations: a new sculpturing tool

Modelling tools tend to virtual sculpturing, in which a basic object is deformed by user supplied actions. The model we present aims to be generic: whatever the geometric description of the object, we can deform it to satisfy location constraints. Our model deforms the whole space, the image of a point is a blend of deformation functions with a projection matrix which allows the satisfaction of the constraints. The user can define the extent of the deformation (i.e. the part of the object to be deformed), the shape of the deformation function to create profiles and the displacement of the constraint points to be satisfied.

Field-of-view tests for a virtual cockpit application

The virtual cockpit application aims to perform ergonom- ics studies on future aircraft cockpits, directly from digital mock-ups. This is made possible by immersing a user in a digital mock-up with the help of virtual reality devices. The challenge is then to reproduce a realistic and exact visual environment. To do that, some visual criteria have to be determined: the necessary values of visual acuity, temporal resolution, and field of view. Some of them are easy to find, but the field-of-view requirement is far more subjective and complex to evaluate. We present tests which have helped us to determine the necessary and sufficient values of field of view for such an ap- plication. We advise then to use a field of view higher than 75 deg, for ergonomic studies and good performances of the users, and up to 133 deg to increase visual comfort. These results will be used for the specification of a head-mounted display for the application.

Conversion d'un carreau de Bézier rationnel biquadratique en un carreau de cyclide de Dupin quartique

Dupin cyclides were introduced in 1822 by the French mathematician C-P. Dupin. They are algebraic surfaces of degree 3 or 4. The set of geometric properties of these surfaces has encouraged an increasing interest in using them for geometric modeling. A couple of algorithmes is already developed to convert a Dupin cyclide patch into a rational biquadratic Bezier patch. In this paper, we consider the inverse problem: we investigate the conditions of convertibility of a Bezier patch into a Dupin cyclide one, and we present a conversion algorithm to compute the parameters of a Dupin cyclide with the boundary of the patch that corresponds to the given Bezier patch.

Virtual immersive review for car design

In this paper, a method to link CAD models to an immersive virtual environment is proposed. CAD models cannot be viewed directly in a real-time visualization environment. CAD models have to be adapted to be viewed in an immersive environment with high quality rendering. The proposed method allows design review in application requesting high quality complex scene visualization in immersive virtual environment. Our application is dedicated to an immersive room called the MoVE (Mobile Virtual Environment). This display offers a particular place to the user. User is inside the virtual world. This position allows us to take care of the peripheral.

Curvilinear constraints for free form deformations on subdivision surfaces

This paper presents a method to deform a subdivision surface with curvilinear constraints. It combines an intuitive free form deformation with a Loop subdivision algorithm. The main advantage of this method of deformation is that it uses only vertices of an object and satisfies the geometrical constraints provided by the user. It permits us to control the final shape of the deformed object, defining the range (i.e. the impact) of the deformation before applying it. The deformation takes into account the Loop properties to follow the subdivision scheme, allowing the user to fix some curvilinear constraints at the subdivision level he works on and to render the final object at the level he wants to. As the deformation uses an influence area defined by the user, we have implemented an adaptive object subdivision driven by the deformation influence.

The Local Fractional Derivative of Fractal Curves

Fractal curves described by iterated function system (IFS) are generally non-integer derivative. For that we use fractional derivative to investigate differentiability of this curves. We propose a method to calculate local fractional derivative of a curve from IFS property. Also we give some examples of IFS representing the slopes of the right and left half-tangent of the fractal curves.

A graph based algorithm for intersection of subdivision surfaces

Computing surface intersections is a fundamental problem in geometric modeling. Any boolean operation can be seen as an intersection calculation followed by a selection of the parts necessary for building the surface of the resulting object. A robust and efficient algorithm to compute intersection on subdivision surfaces (surfaces generated by the Loop scheme) is proposed here. This algorithm relies on the concept of a bipartite graph which allows the reduction of the number of faces intersection tests. Intersection computations are accelerated by the use of the bipartite graph and the neighborhood of intersecting faces at a given level of subdivision to deduce intersecting faces at the following levels of subdivision.

Toward a real-time tracking of dense point-sampled geometry

In this paper, we address the problem of tracking temporal deformations between two arbitrary densely sampled point-based surfaces. We propose an intuitive and efficient resolution to the point matching problem within two frames of a sequence. The proposed method utilizes two distinct space partition trees, one for each point cloud, which both are defined on a unique discrete space. Our method takes advantage of multi-resolution concerns, voxel adjacency relations, and a specific distance function. Experimental results obtained from both simulated and real reconstructed data sets demonstrate that the proposed method can handle efficiently the tracking process even for very large point clouds. Moreover, our method is easy to implement and very fast, which provides possibilities for real-time tracking applications.

A Geometric Algorithm for Ray/Bézier Surfaces Intersection Using Quasi-Interpolating Control Net

In this paper, we present a new geometric algorithm to compute the intersection between a ray and a rectangular Bezier patch. The novelty of our approach resides in the use of bounds of the difference between a Bezier patch and its quasi-interpolating control net. The quasi-interpolating polygon of a Bezier surface of arbitrary degree approximates the limit surface within a precision that is function of the second order difference of the control points, which allows for very simple projections and 2D intersection tests to determine sub-patches containing a potential intersection. Our algorithm is simple, because it only determines a 2D parametric interval containing the solution, and efficient because the quasi-interpolating polygon is directly computed, which avoids both minimum or maximum evaluations of the basis functions or complex envelops construction.