# Clip Worker

Processes clip operations to extract features within a boundary.

## Overview

The clip worker extracts features from a dataset that intersect with a clipping boundary geometry.

## Job Type

`clip`

## Input Parameters

```json
{
  "dataset_id": 123,
  "clip_geometry": {
    "type": "Polygon",
    "coordinates": [ ... ]
  },
  "output_dataset_id": 124
}
```

### Parameters

- `dataset_id` (required): Source dataset ID
- `clip_geometry` (required): GeoJSON geometry for clipping boundary
- `output_dataset_id` (required): Output dataset ID

## Output

Creates a new dataset with clipped features:

- Features that intersect the clipping boundary
- Geometry clipped to boundary
- Original attributes preserved

## Algorithm

The worker uses PostGIS `ST_Intersection` to:

1. Transform clipping geometry to dataset SRID
2. Find features that intersect the boundary
3. Clip geometries to boundary
4. Store results in output table

## Example

```bash
# Enqueue a clip job via API
curl -X POST "https://example.com/api/datasets_clip_run.php" \
  -H "Content-Type: application/json" \
  -d '{
    "dataset_id": 123,
    "clip_geometry": {
      "type": "Polygon",
      "coordinates": [[[-180, -90], [180, -90], [180, 90], [-180, 90], [-180, -90]]]
    },
    "output_dataset_id": 124
  }'
```

## Background Jobs

This analysis runs as a background job. The worker:

1. Fetches queued `clip` jobs
2. Validates input parameters
3. Executes PostGIS clip queries
4. Creates output dataset
5. Marks job as completed

## Performance Considerations

- Processing time depends on dataset size and boundary complexity
- Complex clipping boundaries may slow processing
- Spatial indexes improve intersection performance
- Consider simplifying geometries before clipping

## Related Documentation

- [Clip Analysis Tool](../analysis-tools/clip.md)
- [Analysis API](../api/analysis.md)
- [Workers Overview](index.md)