Animating Lava Flows

Dan Stora, Pierre-Olivier Agliati, Marie-Paule Cani , Fabrice Neyret , Jean-Dominique Gascuel


Version franšaise


Index

  Aims and Scope
  Some results

  Physically-based simulation of the flow
  Large-scale geometry of the flow surface
  Rendering lava crust

  Publications and related works




Aims and Scope

  Motivation: Natural Phenomena
  Aim: Visually-realistic animation of lava flows.
  Difficulty: Both viscosity and surface aspect depend on temperature. They should vary consistently over time.
  Our approach consists in using two completely different scales for computing large scale motion and deformation of the flow on one hand (see Physically-based simulation), and for modelling lava-crust surface details on the other hand (see Rendering lava crust).




Some Results



flow simulation using particles


Animation of a textured lava-flow

More images can be found in the rendering section.





Physically-based Animation of Lava-Flows

Dan Stora, Pierre-Olivier Agliati, Marie-Paule Cani, Jean-Dominique Gascuel.


  We use smoothed particles for computing the physically-based animation of the fluid. This model, where particles are governed by a state equation, was developped by Mathieu Desbrun during his PhD.
  We extended this model in order to introduce a temperature parameter and to model both heat transfers inside the material and transfers with the exterior (air, ground).
  Mass-density is constant, while viscosity exponentially increases when temperature decreases.
  A specific data-structure is used for computing particles interaction forces in quasi-linear time.





Large-scale geometry of the flow surface

Pierre-Olivier Agliati, Dan Stora, Fabrice Neyret, Marie-Paule Cani.


  An Implicit Surface generated by the particles is used for associating a surface to the flow.
  The implicit surface is tiled into Voronoi regions associated with the projection onto the surface of flow particles that lay near the interface with the air or with the ground.





Rendering Lava Crust

Fabrice Neyret.

The particles represent a scale about one meter or one decameter large. To represent smaller scale, we build a 3D dressing, very detailed but purely qualitative, which adds appearance realism to motion realism.

  The purpose is to figure a lava surface that is initially liquid and smooth, which becomes more rough with time. Then more rigid islands (solidified foam) progressively appear on it, and grow with time by aggregating, up to joining each others. Once the crust is solidified, these islands appear as large stones conveyed by the deep lava river, which finaly stop when the thickness of the rigid crust prevents for any motion (even if the heart is still ductile).

  We choose to associate an island to each particle of the motion simulation. As stated above, we define a flow surface, on which we project the particles of the external layer. The Voronoi diagram of these points defines the islands. An island thus corresponds to a set of triangles, whose one vertex is at the island center (i.e. on a surface particle) and the two others are on the border.

rendering of a crust island (real time)

  Thus we just have to build a single lava crust rendering primitive to draw this triangle. This primitive has an analytical component, which models an ideal stone profile (high at the center, low on the border), and a stochastic component which figures the surface roughness, obtained by the use of Perlin noise. The parameters of these two components depend of the temperature, which is known at the vertices (the roughness increase with viscosity, the stone profile appears progressively). A constraint is that these `3D' triangles have to join on a continous way for height and normals, despite they are defined using different frames.

rendering of the lava flow




Publications and Related Works

Animating Lava Flows.
D. Stora, P.O. Agliati, M.P. Cani, F. Neyret & J.D. Gascuel.
Graphics Interface'99, Kingston, Canada, jun 1999.


Related work on texturing triangular domains while ensuring continuity constraints:

Pattern-based Texturing Revisited.
F. Neyret and M.P. Cani
SIGGRAPH 99, aug 1999.


Related works on animating highly deformable materials:

Simulating Landslides for Natural Disaster Prevention.
J.D. Gascuel, M.P. Cani, M. Desbrun, E. Leroy & C. Mirgon.
9th Eurographics Workshop on Computer Animation and Simulation, sept 1998

Smoothed Particles: A new paradigm for animating highly deformable bodies.
M. Desbrun & M.P. Cani-Gascuel.
6th Eurographics Workshop on Animation and Simulation'96, Poitiers, France, sept 96.