Billboard Clouds for Extreme Model Simplification

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Billboard Clouds for Extreme Model
Simplification Décoret, Durand, Sillion
Dorsey In Proceedings of SIGGRAPH 2003
Billboard clouds bridge the gap between
polygon-based and image-based representations.
They afford a high fidelity at extreme levels of
simplification and provide significant rendering
acceleration.
Billboard clouds are novel general primitives
that consist in a set of rectangles with texture
and alpha (transparency) masks.
Texture transparency maps for the rectangles
Input model
Optimal set of rectangles
Billboard cloud rendering
Billboard Cloud Construction
Simplifying a model into a billboard cloud
reduces to the choice of a set of planes that
best approximate the input.
Face
Traditional simplification cannot handle an
object as complex as the Eiffel tower.
Valid plane
Dinosaur simplified to 110 billboards
The planes going through a sphere corresponds to
the envelope between two sheets (in yellow for
the red sphere)
Discretization of the set of planes that are
valid for triangle F
A plane is valid for a face if it goes through
spheres centered on its vertices
Input simplified to 4 planes
Curve of the number of rectangles needed for a
given maximum error (in log-log).
We use a dual space where planes are transformed
into points.
For each point in the dual plane space, we
compute how many triangles it can approximate.
This provides a density in plane space, which we
use to pick the best planes in a greedy fashion.
Castle simplified to 167 billboards
Madcat simplified to 171 billboards
F
dual of F
Dual plane space
Primal space
The set of planes through a point is a sheet in
the dual space. Note that the dual f of f is at
the intersection of the sheets of its vertices
The relighting of a Billboard cloud is enabled by
the storage of normal maps.
Density in plane space. Note the maxima
corresponding to the faces of the house.