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1985 - 19883
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Start date: 1985 × End date: 1989 × Author: Hegron, Gerard ×

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Now showing 1 - 3 of 3
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    An Evaluation of CSG Trees Based on Polyhedral Solids
    (Eurographics Association, 1988) Badouel, Didier; Hegron, Gerard
    Set operation on polyhedra is an important component of Geometric Modeling System (GMS) when a Constructive Solid Geometry (CSG) representation with polyhedral solid primitives is used. Output data will be the unique resulting polyhedron which provides an efficient data structure for displaying objects. With no use of spatial coherency, computational complexity of a set operation is quadratic. The new evaluation scheme called Boolean Octree limits set operation evaluation in a ‘minimal space of calculation’ where primitive boundaries intersect each other and where resulting evaluation participates in the construction of the final resulting object. Boolean Octree computes set operations in a local level providing a linear complexity for geometric calculations. During space subdivision, Boolean Octree has a global view on local CSG tree (projection of the CSG tree in local space) taking into account simplifications of the boolean expression. Set evaluation is done in the local volumes containing only two operands the configurations of which are ‘simple’, that is to say for a local description of an object there is only one vertex with any face number, one edge, or one face.
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    Dynamic Management of 3D Scenes
    (Eurographics Association, 1987) Hegron, Gerard
    When simulating a moving observer or sensor in a 3D scene which contains a large number of objects, only the objects lying in the field of view or of interaction, named the local data base, have to be taken into account in order to decrease, at each step, computation time necessary for either image generation or various processings. This paper presents an algorithm which achieves the dynamic management of the local data base, that is to say which manages the set of objects which enter or leave the field of view of an observer (camera, sensor) during its displacement. This method consists, broadly, of the following two steps: a binary space partitioning of the 3D space is performed off-line from the object bounding boxes by means of planes perpendicular to the X, Y and Z axes and a subregion adjacency graph is created; the dynamic management of the local data base is achieved on-line by modelling the bounded bearing volume of the sensor by a cube of R "radius" (half-edge), and by using the adjacency graph, and inclusion and intersection criteria in order to exploit spatial and temporal coherences between each displacement. When the scene data base is very large, the dynamic management of the RAM memory can be done simultaneously by using this method reasoning from the bounding boxes of disjoined sub - scenes.
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    GENERALIZATION OF CONTOUR TRACKING IN IMAGE SYNTHESIS, AND APPLICATION
    (The Eurographics Association, 1985) Hegron, Gerard; C.E. Vandoni
    In this report, we propose to present most of the treatments about convex and nonconvex colored shapes from a data structure of their contour which is the general approach of contour tracking . Contour filling and oblique cross-hatching take advantage of the coherence between adjacent scan lines and adjacent hatching lines. The position of a point with respect to a nonconvex polygon is solved from filling logic, and the clipping of a line segment by a nonconvex polygon uses the slant cross-hatching idea. We present the clipping of the two nonconvex polygon set. From the area filling of non polygonal blobs, contour tracking is generalized to three geometric problems : position of a point, clipping of a line segment and of a circular arc by a non-polygonal contour, Finally, we discuss the general advantages of contour tracking and application in the writing of a text in a nonconvex polygon.