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How do the other kernels e.g. Parasolid work without seam edges? Without a seam the 2D parametric boundary is not closed.
by loftsy 10mo ago
How do the other kernels e.g. Parasolid work without seam edges? Without a seam the 2D parametric boundary is not closed.
- throwup238 10mo agoIt’s not about seams in 2d but 3d curved surfaces. OpenCascade’s kernel forces you to deal with periodicity in topology (the shape structure), while Parasolid handles it in geometry (the math). A cylinder is mathematically continuous because there's no actual "seam" where it starts and ends. But in OpenCascade there’s a seam from 0 to 2π and this seam edge becomes a real topological entity that every algorithm has to deal with. In Parasolid the cylinder is periodic so when you query a point at U=2.1π, the kernel just knows that's equivalent to U=0.1π. The periodicity is a property of the surface math, not the shape structure. It’s not using polygons/edges/vertexes but a system of equations to calculate the surfaces. This is why boolean ops fail so often in FreeCAD: it’s asking the kernel to intersect with an artificial edge that shouldn't exist. The seam creates edge cases in intersection calculations, makes filleting near seams a nightmare, and complicates things. Parasolid's implicit handling requires smarter surface evaluation code upfront, but then everything else just works.
- thenobsta 10mo agoIs there any canonical literature on this? I've been interested in what's inside the brep kernels recently.
- throwup238 10mo agoBoundary Representation Modelling Techniques by Stroud is probably the most popular one. It's expensive but Anna has it in her archive.
- thenobsta 10mo agoThanks!