# GeoIntel Kempen — Vector Operations Specification v1.0

Vector operations are implemented with GeoPandas/Shapely in the backend and optionally accelerated through PostGIS.

## Global requirements

- Always validate CRS before spatial operations.
- Use metric CRS for area, length and distance calculations.
- Repair invalid geometries before operations.
- Return operation metadata with input dataset ids and parameters.
- Persist important outputs as derived layers.

## Required V1 operations

## 1. Metadata extraction

Input: vector dataset.

Output:

```json
{
  "feature_count": 1234,
  "geometry_types": ["Polygon"],
  "crs": "EPSG:31370",
  "bounds": [xmin, ymin, xmax, ymax],
  "columns": [{"name":"type","dtype":"str"}]
}
```

## 2. Reproject

Input:

- vector dataset
- target CRS

Output:

- reprojected layer
- operation log

## 3. Clip

Input:

- vector dataset
- area polygon

Output:

- clipped layer
- metrics: before/after feature count, retained area/length

## 4. Buffer

Input:

- vector dataset
- distance in meters
- dissolve boolean

Output:

- buffer polygon layer

## 5. Intersect

Input:

- layer A
- layer B

Output:

- intersection layer
- area/length metrics

## 6. Difference

Input:

- layer A
- layer B

Output:

- geometries in A not covered by B

Use case: changed features, missing reference coverage.

## 7. Spatial join

Input:

- target layer
- join layer
- predicate: intersects, within, contains, nearest

Output:

- joined attributes
- match count

## 8. Dissolve

Input:

- vector layer
- optional group field

Output:

- dissolved geometries

Use case: combine green patches, merge detection masks.

## 9. Polygonize from raster mask

Input:

- binary or class raster mask

Output:

- polygon layer with class values

This is technically raster-to-vector but must produce vector layers compatible with all vector operations.

## API shape

Vector operations should be available as jobs:

```http
POST /vector/operations/clip
POST /vector/operations/buffer
POST /vector/operations/intersect
POST /vector/operations/difference
POST /vector/operations/spatial-join
POST /vector/operations/dissolve
```

Each returns a job id and later a derived dataset/layer id.

## Error handling

Return clear validation errors for:

- missing CRS
- unsupported geometry type
- invalid geometry repair failure
- empty output after clipping
- projection failure

## Test fixtures

Create small fixture GeoJSON files for:

- building polygons
- road lines
- area polygon
- reference/prediction polygons for QA