# VDA-FS Files: What They Are and How to Open Them Online

A .vda file is a VDA-FS surface export from the German automotive industry. Learn what VDA-FS stores, how to open one online, what the preview simplifies and when to ask for STEP instead.

A `.vda` (or `.vdafs`) file is a VDA-FS file. VDA-FS is the surface interface defined by the German automotive association VDA and standardised as DIN 66301. It was built to move free-form body and tooling surfaces between CAD systems, and suppliers still receive it from automotive and robot manufacturers alongside STEP and IGES.

You can open a VDA-FS file in [the CADProps workspace](https://www.cadprops.com/workspace/index.md). It samples the surfaces into an approximate triangle mesh, so you can rotate the model, hide groups, check the bounding box, measure point-to-point distances and export STL, OBJ, GLB, glTF, 3MF or mesh STEP after sign-in. It does not give back exact surfaces for machining or a solid model.

## What a VDA-FS file contains

VDA-FS is plain text in fixed 80-column records. The file starts with a `HEADER` block of free text, then lists named entities such as `CURVE01 = CURVE / ...`. The geometry is polynomial: a surface is a grid of patches, and each patch is a polynomial in two parameters.

| Entity | Meaning | Shown in CADProps |
|---|---|---|
| `SURF` | Polynomial surface made of patches | Yes, as triangles |
| `FACE` with `CONS` | Surface trimmed by curves on the surface | Yes, trimmed on a sampled grid |
| `CURVE` | Polynomial space curve | Yes, as lines |
| `GROUP`, `SET`, `BEGINSET`/`ENDSET` | Named collections | Yes, as parts |
| `TMAT`, `TLIST` | Transformations and placed copies | Yes |
| `POINT`, `PSET`, `MDI` | Points and point vectors | No |
| `TOP` | Adjacency between faces | No |

## Units are millimetres

The VDA-FS specification fixes coordinates in millimetres, so CADProps marks the scale as verified and does not ask you to guess it. A file whose header declares a different unit is rejected rather than rescaled. Area and bounding box come from the sampled mesh and are approximate.

Volume and calculated mass appear only when the sampled mesh is closed. Most VDA-FS exports are separate trimmed surfaces with small gaps between faces, so volume is usually unavailable; see [watertight meshes](https://www.cadprops.com/guides/watertight-cad-mesh/index.md) for why.

## What the preview simplifies

The preview is built for fast viewing, not for surface quality checks:

- Each patch is sampled on a small grid, so curvature shows as flat facets. The [tessellation guide](https://www.cadprops.com/guides/cad-tessellation/index.md) explains the trade-off.
- Trim loops are applied on that grid, so trimmed edges can look jagged and very small faces may be left out.
- When a trim cannot be applied, that face is omitted instead of showing the untrimmed surface. The model is then marked incomplete and partial properties are turned off.
- Colours, points and face adjacency are not read.

If you need exact surfaces, continuity checks or a solid, ask the sender for STEP. VDA-FS has no solid topology of its own, and a mesh made from it cannot be turned back into [B-Rep](https://www.cadprops.com/guides/what-is-brep/index.md). The [format matrix](https://www.cadprops.com/supported-formats/index.md) lists every input and its limits.

## Related reading

- [CAD Tessellation: When a Solid Becomes a Triangle Mesh](https://www.cadprops.com/guides/cad-tessellation/index.md)
- [IGES File (.igs, .iges): What It Is and How to Open It](https://www.cadprops.com/guides/iges-file-what-it-is-how-to-open/index.md)
- [Open a Rhino 3DM File Without Rhino](https://www.cadprops.com/guides/open-3dm-without-rhino/index.md)
- [Open CAD Files on Mac: STEP Viewers and Format Options](https://www.cadprops.com/guides/open-cad-files-on-mac/index.md)
- [X3D and X3DV Files: What They Are and How to Open Them Online](https://www.cadprops.com/guides/open-x3d-file-online/index.md)
- [Watertight Mesh: When an STL Can Have a Volume](https://www.cadprops.com/guides/watertight-cad-mesh/index.md)
- [What B-Rep Means in a STEP or IGES File](https://www.cadprops.com/guides/what-is-brep/index.md)

Original article: https://www.cadprops.com/guides/open-vda-file-online/

HTML page: https://www.cadprops.com/guides/open-vda-file-online/