Gérard Hégron

Computer Animation and Simulation 96

The simulation of landslide hazards is a key point in the prevention of natural disasters, since it enables to compute risk maps and helps to design protection works. We present a 3D simulator that handles both rock-falls and mud-flows. The terrain model is built from geological and vegetation maps, superimposed on a DEM. Since the exact elevation of the terrain is unknown at the rocks scale, the simulator uses a series of stochastic simulations, where low scale geometry is slightly randomized at each impact, to compute an envelop of risk areas. Computations are optimized using an implicit formulation of surfaces and a space-time adaptive algorithm for animating the particle system that represents the mud flow.

A Declarative Design Method for 3D Scene Sketch Modeling

In this paper, we present a dynamic model associated with an intelligent CAD system aiming at the modeling of an architectural scene sketch. Our design methodology has been developed to simulate the process of a user who tries to give a description of a scene from a set of mental images. The scene creation is based on a script which describes the environment from the point of view of an observer who moves across the scene. The system is based on a declarative method viewed as a stepwise refinement process. For the scene representation, a qualitative model is used to describe the objects in terms of attributes, functions, methods and components. The links between objects and their components are expressed by a hierarchical structure, and a description of spatial configurations is given by using locative relations. The set of solutions consistent with the description is usually infinite. So, either one scene consistent with this description is calculated and visualized, or reasons of inconsistency are notified to the user. The resolution process consists of two steps: firstly a logical inference checks the consistency of the topological description, and secondly an optimization algorithm deals with the global description and provides a solution. Two examples illustrate our design methodology and the calculation of a scene model.