[Back to Blog](/blog) # Teigha BIM: Faceted Topologies

Ivan Shulga December 21, 2017 [\#rvt](/blog/tag/rvt) [\#rfa](/blog/tag/rfa) [\#getting started](/blog/tag/getting-started)

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There are several types of faceted topology objects in Teigha BIM. Each type has four different parameters:

- Max points
- Precision
- Presence of offset
- Flags

The following is a table of facet topology differences:

| Type | Max points | Precision | Offset | Edge visibility flags |
| :---: | :---: | :---: | :---: | :---: |
| FacetedTopology0 | 64K | Single | - | - |
| FacetedTopology1 | 4M | Single | - | - |
| FacetedTopology2 | 64K | Single | + | - |
| FacetedTopology3 | 4M | Single | + | - |
| FacetedTopology4 | 64K | Double | - | - |
| FacetedTopology5 | 4M | Double | - | - |
| FacetedTopology8 | 64K | Single | - | + |
| FacetedTopology9 | 4M | Single | - | + |
| FacetedTopology10 | 64K | Single | + | + |
| FacetedTopology11 | 4M | Single | + | + |
| FacetedTopology12 | 64K | Double | - | + |
| FacetedTopology13 | 4M | Double | - | + |

As you can see, there are pros and cons to these types of facet topologies:

- Max Points — A container for faceted topologies with 4M points occupies more memory, but it can represent a more detailed model (up to 4 million points can be used).
- Precision — A container with double precision values (“double”) is more precise but takes two times the memory than single-precision (“float”): 8 bytes instead of 4 bytes for each point.
- Offset — An additional 3D-based value allows for the possibility to add the object’s offset, but it allocates more memory.
- Edges visibility flags — More memory is needed for these flags, but it gives additional advantages in special cases.

To create various faceted topologies, the Teigha BIM “BmMasterImportSymbolGPolyMesh\_20009\_ISH“ test was created (you can find it in \\Bim\\Tests\\TB\_UnitTests\\BmMasterImportSymbolGPolyMesh\_20009.cpp). It demonstrates the creation of different faceted topologies, including import from an .stl file.

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