# needInterpolation ([`Case`](index.md))

Controls how FELiCS imports the mean-flow fields onto the computational mesh.

<dl>
  <dt><strong>Type</strong></dt>
  <dd><em>boolean</em></dd>

  <dt><strong>Default</strong></dt>
  <dd><code>true</code></dd>
</dl>

### Example
```json
"Case": {
    "needInterpolation": true
}
```

**When `needInterpolation` is set to `true`:** FELiCS assumes that the mean flow is provided on a grid that differs from the degrees of freedom of the computational mesh. The mean-flow fields are then imported using linear interpolation onto the FEM domain defined by the [`mesh file`](../../gmsh_files.md).

➡️ This is typically used when loading mean-flow files defined on CFD grids, such as `.fel` files.

**When `needInterpolation` is set to `false`:** FELiCS assumes that the mean flow was already exported by FELiCS from the same computational grid as the current run. In this case, FELiCS maps the degrees of freedom of the imported fields, stored with the exported FELiCS mesh, to the current FEM spaces. This skips the interpolation step, which can significantly reduce preprocessing time for large 3D cases.

➡️ This is typically used when reloading `MeanFlow.h5` files generated by a previous FELiCS run.