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Direct Manipulation of Free-Form Deformations

William M. Hsu, John F. Hughes, Henry Kaufman

SIGGRAPHAcademicSkinning

Lets the user drag points on the model directly and solves for the lattice control points that achieve it, making FFD usable without manipulating the cage by hand.

Abstract

Makes free-form deformation directly manipulable. Instead of moving lattice control points and watching the embedded model follow, the user picks and drags points on the object itself, and the system solves, via a least-squares pseudo-inverse, for the control-point movements that best produce the requested surface motion. This turns FFD from an indirect lattice-first tool into one where the artist edits the shape directly, a key step toward practical deformation interfaces.

How to read this

Category
Method: direct-manipulation interface for free-form deformation
Contributions
  • Lets the user drag points on the model rather than lattice control points
  • Solves for the control-point motion via a least-squares pseudo-inverse
  • Turns FFD into a direct shape-editing tool
Context
Builds on Free-Form Deformation and Extended FFD, fixing their main usability problem: editing the cage instead of the shape.Builds on: Free-Form Deformation of Solid Geometric Models · Extended Free-Form Deformation: A Sculpturing Tool for 3D Geometric Modeling
Correctness
Correct and practical; the pseudo-inverse gives a least-norm solution, so edits can be under-determined and need sensible point choices.
Clarity
Readable; the manipulation idea is intuitive and the math is compact.
How to read it
First pass: the drag-the-surface idea and why it matters. Second pass: the least-squares solve mapping surface motion back to control points.

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