# About Tessellation

> What tessellation is and how it works in Asset Transformer Studio

> **Note:**
>
> Have a look at [About 3D Models Types](/asset-transformer-studio/2026.5.0/manual/data-preparation-fundamentals/about-3d-models-types.md) to understand the difference between CAD models and polygonal models.

To be displayed in a 3D application, **CAD models' faces need to be translated into tessellated surfaces, also called meshes**.

A mesh is composed of multiple connected polygons, or triangles (1 polygon generally equals 2 coplanar triangles), forming a discretized geometry that is understandable by a [GPU](https://en.wikipedia.org/wiki/Graphics_processing_unit), to be rendered in a 3D application.

The more triangles used to represent a surface, the more realistic the rendering, but the more computation is required.

![Tessellation example](/api/media?file=/asset-transformer-studio/2026.5.0/media/ALGO_Tessellate.jpg)

The tessellation step is very important in data preparation as it defines the maximum quality of the CAD model. The tessellation algorithm [has proven to be very efficient](https://create.unity3d.com/benchmark-report-pixyz) at transforming any CAD model into meshes, ready to be displayed and exported, with a **perfect balance between visual quality and polygon count**.

The **Tessellate** function is available from the [CAD](/asset-transformer-studio/2026.5.0/manual/user-interface/menu-bar/cad-menu.md) menu.

> **Note:**
>
> Want to learn more about the process of tessellating CAD models? Have a look at [this keynote](https://youtu.be/BNUZLnhCR2Q?t=156)!

![Tessellation result](/api/media?file=/asset-transformer-studio/2026.5.0/media/NewItem8.png)

## Parameters

Several parameters are used to control the tessellation, the most important ones being:

| Parameter      | Description                                                                                                                                                                                                                                                                                                                                                                  |
| -------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Max Sag**    | The maximum distance between the geometry and the tessellation (also called "Chord error"). This parameter ensures that the mesh is similar enough to the original analytical CAD surface (exact geometry). A low value means that a very fine mesh is created. The distance values are expressed in millimeters.                                                            |
| **Max Angle**  | The maximum angle allowed between normals of two adjacent polygons (on the same face). This provides more precision on small radius fillets. Adjust the `Max angle` parameter to keep enough polygons in high curvature areas whose radius is lower than the `Max Sag` value, like fillets for example.                                                                      |
| **Max Length** | Used to control the maximum length of a polygon (edge). For rendering, it is often recommended not to use the `Max Length` parameter. It increases the polygon count without significant improvement on the visual aspect. But in case of very long objects (a plane body, a train cabin…), this setting can avoid lighting artifacts caused by too long/stretched polygons. |

![Tessellation parameters](/api/media?file=/asset-transformer-studio/2026.5.0/media/NewItem406.png)

## Example

In the example below, reducing the `Max Sag` value from 0.2mm to 0.1mm made the mesh less rough and more realistic:

![Sag parameter effect](/api/media?file=/asset-transformer-studio/2026.5.0/media/ALGO_Tessellate_ParameterSag.gif)

Then, adding the `Max angle` parameter (with a 20° value) has improved fillet precision by adding a row of polygons without increasing the polygon count for the yellow piece contour:

![Angle parameter effect](/api/media?file=/asset-transformer-studio/2026.5.0/media/ALGO_Tessellate_ParameterAngle.gif)

## Presets

The **Tessellate** function comes with 4 default presets:

![Tessellation presets](/api/media?file=/asset-transformer-studio/2026.5.0/media/NewItem26.png)

| Preset               | Description                                                                                                                                                                        |
| -------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Low**              | Delivers less accurate meshes. Use this preset for objects that will be seen from a distance, or for large objects with no details that need to be seen.                           |
| **Medium** (default) | Delivers well-balanced meshes. It is the default preset that will give the best result in most situations, **a good average between polycount and visual quality**.                |
| **High**             | Delivers more detailed meshes. Use this preset for objects that will be observed more closely (close to the virtual camera), or for objects that have small and important details. |
| **Very High**        | Delivers super-detailed meshes. Use for objects that have small details that are important, or for very small objects, like rings, microchips…                                     |

![Presets comparison](/api/media?file=/asset-transformer-studio/2026.5.0/media/ALGO_Tessellate_Presets.gif)

The difference of quality is very hard to distinguish, especially between `Medium` and `High` presets. With `Low` preset, the lack of polygons is starting to show.

This demonstrates that **using the `Medium` preset is most of the time the best solution**, especially if you do not need to zoom closely on the model's details.

> **Note:**
>
> Once you have found the perfect set of tessellation parameters that gives the quality you need, save them in a new preset!

## Tessellation and Part size

The `Max Sag` is a distance criterion: a smaller value is necessary to guarantee a sufficient quantity of polygons on small parts.

A bigger [Part](/asset-transformer-studio/2026.5.0/manual/data-preparation-fundamentals/about-occurrences/occurrence-types.md) in terms of scale does not mean that this part does not contain some potentially important details.

So, a small Sag value can also be used to maintain quality on detailed areas of bigger parts.

In the below example, the red beam (way bigger than the yellow ring) was tessellated with a *5 mm* Sag, and *0.1 mm* for the ring.

The result is that the hole in the beam was turned into a square: details on a big part were lost.

![Tessellation and size](/api/media?file=/asset-transformer-studio/2026.5.0/media/NewItem75.jpg)

In a general approach, the best strategy is to find criteria (size, material, any metadata…) to perform a targeted tessellation, with different settings, based on these criteria.

## About Re-tessellate

Models that contain BRep surfaces (CAD models) can be retessellated directly in the scene without having to import the model all over again. [Re-Tessellate](/asset-transformer-studio/2026.5.0/manual/data-preparation-fundamentals/about-tessellation/re-tessellate.md) allows you to fine-tune tessellation quality of entire models or individual parts in the scene.

## Related topics

* [About 3D Models Types](/asset-transformer-studio/2026.5.0/manual/data-preparation-fundamentals/about-3d-models-types.md)
* [Re-Tessellate](/asset-transformer-studio/2026.5.0/manual/data-preparation-fundamentals/about-tessellation/re-tessellate.md)
* [About Decimation](/asset-transformer-studio/2026.5.0/manual/data-preparation-fundamentals/about-decimation.md)