Internal organ
animation
SC 24 WG 9 & Web3D Meeting
Jung-Ju Choi
Ajou University
Motion of internal organs
Objectives
To represent the motion of internal organs such as a heart, lungs, a
liver, and so on.
Internal organs
Some move likely by themselves, such as a heart
• Cardiac muscles are involuntary muscles
Some move only likely by means of external force, such as a liver
• A liver does not seem to move autonomic
All respond to the external force
• Because they are basically soft
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 2
Motion of internal organs
Representation
High-resolution 3D mesh
Physically-based deformation simulation for soft objects
• Multiresolution editing
Region-based animation for autonomic organs
• Partition a heart, for e.g., into several regions
• Collect the time-series representative poses and define them as
keyframes
• Represent the poses by means of regions
- Details are very similar to the facial animation of H-Anim
Should be physically plausible and look natural
• May not be physically correct
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 3
Physically-based Deformation
Elastic energy
How much the object is deformed from its initial configuration
Stretching and bending energy for thin shell objects
Can be measured by the first and second fundamental forms
S: 2-manifold surface in R^3 parameterized by x in R^2 such that
•
S’: a deformed surface from S by adding a displacement d(u,v) to each
point x(u,v)
• S’ = x’(U) with x’(u,v) = x(u,v) + d(u,v)
The elastic energy E of S’ is defined by
•
, where
• I and II are the first and second fundamental forms, and
•
and
are stretch and bending resistance coefficients
For physically plausible deformation, we try to minimize E(S’) at every
frame with a fixed part (handle) of S’
Linearization and triangulation techniques for the elastic energy
computation makes physically plausible deformation done in real-time
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 4
Multi-resolution Deformation
Multi-resolution techniques are required to achieve detail
preservation while using a linear deformation technique
Partition the surface S into a base surface B and a detail surface D
B is deformed to B’
S’ is composed by B’+D
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 5
Animating Internal organs
In order to animate autonomic internal organs such as a
heart,
Taking representative poses as keyframes from real motion examples,
• Where poses can be represented by positions of handles (a part of organs)
Animating by interpolation of handles in keyframes
• The other part of organs (except of handles) can be computed by
physically-based deformation or other techniques
We can adopt the basic idea of facial animation in H-Anim
• A preliminary experiment is shown in the next slide
We need to partition an organ into several parts so as to
define handles
Anatomy-based partition and anatomist’s consultation may be
required for the modeling and animation of internal organs
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 6
Preliminary experiment
Ground truth motion Reconstructed motion
For a ball-shaped soft object, we adopt the same approach
to the facial animation in H-Anim.
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Preliminary experiment
Information of geometry and motion
Size: 6.62381 x 6.81732 x 6.623381
Number of frames: 360
Number of vertices: 1562
Number of regions: 58
Number of region boundary vertices: 477
Number of internal vertices: 1085
Average RMSE for all vertices: 0.00308823
Average RMSE for internal vertices: 0.00360652
Average RMSE for boundary vertices: 0.00086921
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 8
Preliminary experiments
Some artifacts are observed when an object deforms big
Source
Reconstruction
Source
Reconstruction
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 9
More Experiments
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 10
Silicon Studio, Korea https://www.youtube.com/watch?v=g81AEvfxMiA
Things to do for internal organs
Reference implementation of physically-based deformation
Applying region-based animation for internal organs
Partition (or partition hierarchy) of internal organs in order
for
Realistic modeling,
Physically plausible deformation, and
Naturally looking animation
Biometry-based deformation and animation, for e.g.
Animation of a heart motion (cardiomotility) based on heart rate
Deformation of a liver based on liver hardening (hepacirrhosis)
......
We may use measured bio-signal for the animation and deformation
of internal organs
Jan. 16, 2017 SC 24 WG 9 & Web3D Meeting, Seoul, Korea 11
