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In a recent blog post (Healing and Preserving 3D Model Intent) and eBook (Healing as an Essential Function), we wrote about the healing process within the 3D ACIS Modeler and 3D InterOp on precise (B-rep) models. To recap, healing is the process of modifying model data so that it conforms to the rules of the target system, while adhering to the intent of the source.
The capabilities described in the blog dealt with healing a precise model. But what happens when all or part of the model is tessellated? What is the healing solution for a hybrid model?
Mesh/tessellated data is common to some industries, such as additive manufacturing, medicine, geology, and architecture, or for workflows operating with approximated 3D models. The data can come from LiDar, or from other modeling systems that output stereolithography (STL) files. The most common CAD export format, STL, describes a surface as a collection of connected triangles — the more complex a surface is, the larger number of triangles are needed to define that surface (for more info on STL and the issues that can arise, see the case study, Spatial SDKs: Streamlining Solutions for Metal AM in Renishaw QuantAM.
Because mesh data is an approximated representation of an object/assembly, there are often imperfections in the data which can hinder many downstream workflows, or result in a poorly printed assembly. These imperfections can include:
Because STL is an open format, and subject to interpretation, and contains no topology information (bodies, faces, etc.), exported STL data can contain additional errors:
All of these potential issues with imported tessellated data make healing mandatory.
For a tessellated model, healing involves repairing the mesh to better represent the scanned object or the original design intent. There are two possible approaches to healing:
Voxel healing, the most powerful global healing routine, creates a volumetric representation of the entire body, remeshing the model to create watertight entities. This approach repairs bad polyhedral geometry, healing improper facet intersections, overlapping facets, incorrect orientations, and degenerate geometries. CGM Polyhedra’s voxel healing provides configurability as to the voxel size and level of detail desired.
Voxel healing is the ultimate easy-button healing approach, able to resolve anomalies where all other solutions fail.
Figure: Before Voxel Healing
Figure: After Voxel Healing
For situations requiring a more hands-on approach, CGM Polyhedra provides the robust ACIS checking API to find and localize problem areas. Then the general healing tools allow a user to assign a topology to a collection of mesh components. There are additional tools that enable users to:
CGM Polyhedra brings healing to hybrid models, providing access to powerful, pushbutton voxel healing. When combined with the healing capabilities within the 3D ACIS Modeler, it provides a robust one-two punch.