Methodology for Tessellation Segmentation

You will find below some information on the methodology of Tessellation Segmentation.

This page discusses:

How to Proceed

Below are listed the recommended steps.

Notes:

Analysis and Healing of the Tessellation

A tessellation of good quality is required.

To achieve this quality:

  • Check the dimensions of the tessellation: Too small a tessellation may lead to segmentation problems.
  • Use Mesh Cleaner in Digitized Shape Preparation to detect and fix irregularities and structural faults.
  • Faults linked to the quality of the emitting system require a visual analysis of the tessellation. We recommend you switch to Flat display mode for a better visualization of faults or to detect overlapping triangles.
    • Example of a bad quality torus

    • Example of a bad quality cone

    • Example of a bad quality area

Note: Healing the tessellation is not compulsory. However, we strongly recommend you heal the tessellation to minimize the need for manual edition, and to improve the BRep quality. For example, this area

leads to a poor quality BRep

These cones

require manual corrections.

Areas Edition

A visual analysis of the segmentation will show you the areas with problems.



Below are listed some solutions:

  • In the dialog box, each area is associated with a green/red diagnostic patch. A red patch indicates a possible problem, such as:
    • A very small area (the three dimensions of the containment box are less than 1mm)
    • Several connex sub-areas within the area
    • An area containing non manifold elements or corrupted or duplicated triangles.
  • Still in the dialog box, order the list by the number of triangles, to detect and analyze areas with few triangles.
  • Propagation by type let you better analyze undefined areas.
  • Do try to recognize basic shapes such as plane, cylinder, torus

    sphere

    and fillets.

  • Do not use the fillet type propagation (shown below)

    on areas corresponding to cylinders (red arrows below) or tori (orange arrow below).

  • Use the brush to merge, separate or define areas more precisely.

  • Use Render Style to navigate inside the tessellation and edit non visible areas.
  • Use Display Edges and Nodes to detect areas with potential problems.

Below are a few edition results:

  • Merging of areas with the interactive brush + CTRL

  • Edition of an edge with the interactive brush

  • Recognition by propagation:
    • Sphere recognition

    • Fillet recognition

  • Manual segmentation of an area in sub-areas, using the interactive brush

Edition of Types

Visualization by type lets you detect areas with an inappropriate type, especially when coupled with Display Edges and Nodes (as you can see the areas topology).

Below are a few tips:

  • Use Fillet for rough fillets.
  • Use FreeSurf for rough surfaces.

Analysis and Edition of the BRep

To assess the quality of the BRep, check that the exact basic shapes are true to the tessellation, and that there are no free edges for connex areas of the tessellation.

When areas do not comply with these criteria, check the segmentation locally:

  • Check the segmentation quality (repartition and typing of the triangles in neighbor areas).
  • Look for possible faults in the tessellation (superimposed triangles, twisted areas).
  • Look for thin triangles.

Even after several re-definitions and typings of the areas, free edges may still be found in the BRep. In such cases, consider going to Generative Shape Design and using Healing to remove them, before generating the solid with Close Surface. For some intricate configurations, consider extracting the invalid faces, to reconstruct them with standard surface creation commands (Fill, Blend,...).

Example

You will find below an example of segmentation.

The input tessellation looks like this:

Analysis of the tessellation
  • The Triangles display mode lets you check that the mesh is indeed a tessellation.

  • Mesh Cleaner does not show irregularities or structural problems.
  • Information lets you check that the tessellation has no free edges.
Automatic Segmentation
Some areas require a manual edition.

Result after:

  • Searching tori and fillets by propagation
  • Merging areas
  • Manual edition with the brush.


Edition of Types


Two areas that are clearly tori have been typed as FreeSurf. Their type must be switched to Torus.

Generation of the BRep
The result can be improved:
  • This is not a solid: the surface cannot be closed because of free edges.
  • The segmentation can be improved.



Edition of Areas and Types
  • Edition near the free edges areas:



  • Modification of the type from Sphere to FreeSurf

Generation of the BRep
Expected result: A solid.