# Loft

The **Loft** module is used to extend the geometry of the terrain, used in CFD Simulations.
The loft extension is essential to guarantee that the terrain starts from a straight line.
Otherwise it would affect the wind flow.

## Use Case

The loft geometry is generated in the **pre-processing** step of the CFD simulations.
In order to use the loft module, the **terrain surface artifact**, from the landscaping project must be generated beforehand.

The process of loft generation and the rotation of the domain to simulate other **wind source directions**
is simplified if the terrain surface has a **cirular shape**, but other shapes can be used.
An example of the shape of the input terrain surface is shown below:

```{image} /_static/loft/terrain.png
:width: 90%
:align: center
```

:::{important}
The user must guarantee that the terrain surface **does not have a hole** in it.
Otherwise, the **border detection will fail!**
:::

## Artifacts

The loft module also has to receive a configuration file containing the **loft parameters**.
The loft parameters define the **geometric properties** of the output surfaces.
An example of the configuration file is shown below:

```{literalinclude} /_static/loft/loft_params.yaml
:language: yaml
```

Calling the loft module will generate the following files:

1. **Upwind and downwind lofts**: Untreated generated loft surfaces.
2. **Upwind and downwind remeshed lofts**: Remeshed loft surfaces with target element size.
3. **Terrain remeshed**: Remeshed terrain surface with target element size.

An example of the expected output file is shown below:

```{image} /_static/loft/loft.png
:width: 90%
:align: center
```

## Usage

To invoke and generate loft surfaces, the following command can be used:

```Bash
uv run python -m cfdmod.loft \
   --config  {CONFIG_PATH}
   --surface {TERRAIN_PATH} \
   --output  {OUTPUT_PATH} \
```

Another way to run the generation, is through the [notebook](generate_loft.ipynb)

```{toctree}
:maxdepth: -1
:hidden:

Loft use case<generate_loft.ipynb>
```