Progressive Combined BReps

We present the Combined BRep as a multiresolution data structure suitable for interactive modeling and visualization of models composed of both free-form and polygonal parts. It is based on a half-edge data structure combined with Catmull/Clark subdivision surfaces. In addition to displaying the curved parts of the surface at an adaptive levelof-detail, the control mesh itself can be changed interactively at runtime using Euler operators. The tesselation of changed parts of the mesh is incrementally updated online. All changes in the mesh are logged, so that a complete undo and redo mechanism can be provided. We introduce Euler macros as a grouping mechanism for Euler operator sequences. The macro dependency graph, a directed acyclic graph, can be used for creating progressively increasing resolutions of the control mesh, and to guide the view-dependent refinement. We consider Combined BReps to be of use for data visualization and interactive 3D modeling, as well as a compact representation of synthetic 3D models.