Abstract:
The complexity of animating trees, shrubs and foliage is an
impediment to the efficient and realistic depiction of natural
environments. This paper presents an algorithm to extract, from a
single video sequence, motion fields of real shrubs under the
influence of wind, and to transfer this motion to the animation of
complex, synthetic 3D plant models. The extracted motion is
retargeted without requiring physical simulation. First, feature
tracking is applied to the video footage, allowing the 2D position
and velocity of automatically identified features to be clustered. A
key contribution of the method is that the hierarchy obtained
through statistical clustering can be used to synthesize a 2D
hierarchical geometric structure of branches that terminates
according to the cut-off threshold of a classification algorithm.
This step extracts both the shape and the motion of a hierarchy of
features groups that are identified as geometrical branches. The 2D
hierarchy is then extended to three dimensions using the estimated
spatial distribution of the features within each group. Another key
contribution is that this 3D hierarchical structure can be
efficiently used as a motion controller to animate any complex 3D
model of similar but non-identical plants using a standard skinning
algorithm. Thus, a single video source of a moving shrub becomes an
input device for a large class of virtual shrubs. We illustrate the
results on two examples of shrubs and one outdoor tree. Extensions
to other outdoor plants are discussed.
Reference:
Diener, J., Reveret, L., Fiume, E."
Hierarchical retargetting of 2D
motion fields to the animation of 3D plant models",
2006
ACM SIGGRAPH/Eurographics Symposium on Computer Animation, SCA'06,,
Vienna, Austria, September 2006.
Paper [PDF,
1.6Mb]
Video [MPEG
29Mb]
