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Localized Verlet Integration Framework for Facial Models

Ozan Cetinaslan, Veronica Orvalho

AMDOAcademic6 citesFacialRigging

Confines Verlet integration to a selected patch of the face, picked by geodesic distance from a heat kernel, so a local deformation does not ripple through the whole model.

Abstract

Traditional Verlet integration frameworks have been successful with their robustness and efficiency to simulate deformable bodies ranging from simple cloth to geometrically complex solids. However, the existing frameworks deform the models as a whole. We present a Verlet integration framework which provides local surface deformation on the selected area of the mesh without giving any global deformation impact to the whole model. The framework is specifically designed for facial surfaces of the cartoon characters in computer animation. Our framework provides an interactive selection of the deformation influence area by using geodesic distance computation based on heat kernel. Additionally, the framework exploits the geometric constraints for stretching, shearing and bending to handle the environmental interactions such as collision. The proposed framework is robust and easy to implement since it is based on highly accurate geodesic distance computation and solving the projected geometric constraints. We demonstrate the benefits of our framework with the results obtained from various facial models to present its potential in terms of practicability and effectiveness.

How to read this

Category
Physically based deformation framework for facial surfaces, aimed at stylised characters.
Contributions
  • A Verlet integration framework that deforms a selected area of the mesh instead of the model as a whole.
  • Interactive selection of the influence region using geodesic distance computed from a heat kernel.
  • Geometric constraints for stretching, shearing and bending, which lets the framework handle collisions and other environmental interaction.
  • A specific target of cartoon character faces rather than photoreal ones.
Context
Follows cetinaslan-sketch-controllers-2015 in the same programme: find ways to edit a face locally. Where the 2015 paper localises the interface, this one localises the solver. The geodesic locality machinery introduced here is the same idea that later bounds the blendshape edits in cetinaslan-sketching-manipulators-2020.Builds on: Sketch-Based Controllers for Blendshape Facial Animation
Correctness
The framework rests on the accuracy of the geodesic computation, which the paper says plainly, and on projected geometric constraints, which are fast but not physically exact. That trade is fine for cartoon faces and would not survive a photoreal soft tissue comparison. The results are qualitative, across various facial models, so read them as evidence of practicability rather than of accuracy.
Clarity
Straightforward once you know Verlet integration and position based dynamics. If you do not, read a position based dynamics primer first or the constraint section will feel like a list.
How to read it
First pass: abstract and results, to see what local deformation buys. Second pass: the geodesic influence region, which is the transferable idea and the one that recurs in the 2020 papers. Third pass: the constraint projection, only if you intend to implement it.

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