# 4 - Preprocess Categrozie Wooded Area
<!-- <div class="algorithm-id">
<strong>Algorithm ID</strong>: <code>hedgetools:preprocesscwa</code>
</div> -->
```{container} algorithm-id
**Algorithm ID**: `hedgetools:preprocesscwa`
```

This tool prepares a tree cover vector layer obtained from [Generate Tree Cover](./generate_tc.md) for the [Categorize Wooded Area](./cwa.md) algorithm.  

Since vector layers created from rasters can be very large,  This tool will:  
- Simplify geometries.  
- Remove holes inside polygons and eliminate small geometries.  
- Repair invalid geometries.

## Parameters

| Label | Name | Type | Description |
|-------|------|------|-------------|
| Input tree cover layer | `INPUT` | [vector: polygon] | Polygon vector layer. |
| Area threshold for geometry deletion (square meters) | `MIN_AREA` | [numeric: double] <br> Default: 20.0 | Geometries smaller than this value will be deleted. |
| Shift tolerance for simplification (meters) | `TOLERANCE` | [numeric: double] <br> Default: 0.25 | Vertices that do not move the polygon boundary beyond this threshold will be removed during simplification. |
| Area threshold for filling polygon holes (square meters) | `HOLE_SIZE` | [numeric: double] <br> Default: 50.0 | Holes smaller than this value will be filled. |
| Output preprocessed tree cover layer | `OUTPUT` | [vector: polygon] <br> Default: `[Create temporary layer]` | Output polygon vector layer. |

```{admonition} Warning
:class: warning
Polygons with many holes can cause issues when splitting them in either [Topological Polygons](../data_preparation/topological_polygon.md) or in the [Data - Transformation](../data_transformation/index.md) module. This may result in incorrect solutions or failures during the splitting process.
```

## Outputs

| Label | Name | Type | Description |
|-------|------|------|-------------|
| Output preprocessed tree cover layer | `OUTPUT` | [vector: polygon] | Preprocessed tree cover vector layer. |