Manifold Geometry // Многообразная Геометрия

Hidden Line Removal / Comparative Study

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One of the upcoming articles will touch on the subject of generating technical drawings. In a typical OpenCascade-based workflow, to generate a PDF drawing, you have to do something like this:

  1. Load a CAD model of interest to a 3D viewer.
  2. Apply hidden line removal (HLR) algorithm that turns the exact 3D shape into a precise projection outline.
  3. Add supplementary labels, tables, annotations and decorations.
  4. Export this whole thing into PDF.

In FreeCAD, this process is handled by the TechDraw workbench. The central bottleneck in the workflow is the HLR algorithm. Since long before I started at OCC 15 years ago, this algorithm has been constantly updated and improved leaving the impression of a never-ending story. With this brief note I want to share a small (and a little outdated) Comparative Study on the OpenCascade's HLR and its quality w.r.t. the commercial products. The conclusion of this study is that OpenCascade's HLR is quite Okay for small assemblies and single parts. We will elaborate on per-part drawing generation in the future series.

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