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. Input model Optimal set of rectangles 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 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 A plane is valid for a face if it goes through spheres centered on its vertices Input simplified to 4 planes We use a dual space where planes are transformed into points. F Primal space The planes going through a sphere corresponds to the envelope between two sheets (in yellow for the red sphere) Dinosaur simplified to 110 billboards Discretization of the set of planes that are valid for triangle F 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. Curve of the number of rectangles needed for a given maximum error (in log-log). Castle simplified to 167 billboards Madcat simplified to 171 billboards dual of F Dual plane 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.
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