Real-time Simulation of Self-Collisions for Virtual Intestinal - - PowerPoint PPT Presentation

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Real-time Simulation of Self-Collisions for Virtual Intestinal - - PowerPoint PPT Presentation

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Real-time Simulation of Self-Collisions for Virtual Intestinal Surgery Laks Raghupathi Vincent Cantin Franois Faure Marie-Paule Cani GRAVIR / IMAG, Grenoble, FRANCE A joint lab of CNRS, INPG, INRIA and UJF June 12, 2003 IS4TM,

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GRAVIR / IMAG, Grenoble, FRANCE A joint lab of CNRS, INPG, INRIA and UJF

June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Real-time Simulation of Self-Collisions for Virtual Intestinal Surgery

Laks Raghupathi Vincent Cantin François Faure Marie-Paule Cani

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Overview

  • Scope

– Surgical trainer for colon cancer removal – Issues: Intestine modeling & collision processing

  • Related Work
  • Contribution

– Geometric and mechanical modeling – Efficient collision processing

  • Results, Demos & Discussion
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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Intestinal Surgery

Laparoscopic technique

Critical task

  • move the small intestine aside

Surgery objective

  • remove cancerous colon tissues

Aim: Train the surgeons to do this task

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Challenges

  • Model the complex anatomy
  • Detect multiple self-collisions
  • Provide a stable collision response

Small l Intestine ine 4 m length, 2 cm thick Mesentery Folded surface 15 cm width Connects intestine with main vessels

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Related Work

Real-time deformable models

  • Multiresolution models [Capell02, Debunne01, Grinspun02]
  • Soft-tissue models [Cotin00, James99, James02, Meseure00]

Objects in isolation or interacting with a rigid tool => Different Situation Skeletal model for intestine [France02]

  • Chain of masses and springs
  • Implicit surface representation for smooth rendering
  • 3D grids for self-collision and collision with environment

Not applicable for mesentery Hierarchical BV detection [Bradshaw02, Cohen95, Gottschalk96, van den Bergen97]

  • Sphere-trees, OBBs, AABBs, etc.

Expensive tree updates for large-scale deformation

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Geometric model

  • Collision-free initial position

M esentery Intestine (4 m ) 10 cm 15 cm Vessel

  • Mesentery surface

– suspends from the vessel

  • Intestine

– borders the mesentery – skinning at rendering

Vessel Mesentery Intestine

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Mechanical model

  • Mass-spring model
  • 100 fixed particles representing vessels
  • 300 animated particles

– 200 particles for the mesentery – 100 particles with modified mass for intestine

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Collision Detection (Intestine)

Aim: Find colliding segments Inspiration

  • Temporal coherence

– Track pairs of closest features

[Lin-Canny92]

  • Handle non-convex objects

– Stochastic sampling [Debunne02]

  • Maintain list of active pairs
  • For each segment-pair
  • Update by local search

M ultiple self-collisions

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Algorithm

  • At each step

– Compute new positions and velocities – Add n pairs by random selection – For each pair:

  • Propagate to a smaller distance

– Remove unwanted pairs – For each pair:

  • if dmin < radius_sum

– Expand to local collision area – Apply collision response

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Collision adapted to mesentery

  • Thin mesentery will have little impact on simulation

 Neglect mesentery-mesentery interaction

  • Mesentery-Intestine: Two-step pair propagation

– Find nearest intestine segment (3 distance computations) – Find nearest mesentery segment (11 distance computations) O(n+m) complexity instead of O(n*m)

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Collision Response

(2) New velocities in terms of unknown f:

' . ) (

new new

r r    u x' x . ) (

new new

  u v' v u f

1

K   v v

new

u f

2

K   v' v'

new

(1) Condition for velocity correction: (3) Solve for f and determine vnew and v’new (4) Similarly, position correction using:

u direction

  • f collision

(x, v) (x’, v’) radius r radius r’

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Validation

O(n²) Stochastic 50 30 10 100 120 17 200 473 27 Number of segments Computation time (ms)

  • Correctness
  • No theoretical proof that all collisions detected
  • Good experimental results for intestine
  • Efficiency
  • Intestine in isolation
  • Intestine + Mesentery: 30 fps with 400 particles on standard PC
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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Demo 1*

*captured at the prototype simulator at LIFL, Lille Skinning based-on [Grisoni03] Hardware: Bi-Athlon 1.2 GHz 512MB with nVIDIA GeForce 3

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Demo 2*

*captured at the prototype simulator at LIFL, Lille

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Conclusions

  • Real-time simulation of complex organs
  • Efficient self-collision detection
  • Work-in-progress

– Optimization of the update algorithm – Use triangles for mesentery collision detection – Handling fast motion for thin objects

  • Continuous-time collision detection
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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Acknowledgements

INRIA ARC SCI Grant

(action de recherche coopérative – Simulateur de Chirurgie Intestinale )

Luc Soler (IRCAD) for anatomical information Laure France (LIFL) for research data Collaborator LIFL, Lille for prototype simulator

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Thank You

http://www-evasion.imag.fr

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June 12, 2003 IS4TM, Juan-Les-Pins, FRANCE

Questions / Comments ?