# GeoIntel Kempen — Change Detection Specification v1.0

Change Detection is a major showcase workflow combining raster, vector, AI and QA/QC.

## Goal

Compare two datasets or analysis runs for the same area and detect additions, removals and significant changes.

## Supported methods

## Method A — Vector change detection V1

Compare two vector layers or two analysis outputs.

Examples:

- GRB buildings snapshot A vs snapshot B.
- AI detections from raster A vs AI detections from raster B.
- OSM buildings from run A vs OSM buildings from run B.

### Inputs

- layer A
- layer B
- area polygon
- class filter optional
- matching threshold

### Algorithm

1. Normalize CRS.
2. Clip both layers to area.
3. Match features using IoU or spatial overlap.
4. Classify:
   - added: feature in B without match in A
   - removed: feature in A without match in B
   - unchanged: matched with stable geometry
   - modified: matched but area or geometry changed above threshold

### Metrics

- added count
- removed count
- modified count
- added area m²
- removed area m²
- net area change m²
- percentage change

## Method B — Raster index change V2

Compare NDVI/NDWI/NDBI rasters.

### Inputs

- index raster A
- index raster B
- threshold

### Algorithm

```text
delta = index_B - index_A
classify pixels by threshold
polygonize changed zones
```

### Outputs

- change raster
- changed polygons
- summary statistics

## Method C — AI segmentation change V3

Run segmentation on both images and compare class polygons.

Examples:

- vegetation loss
- new buildings
- water change

## Output layers

- `change_added`
- `change_removed`
- `change_modified`
- `change_heatmap`
- `change_uncertain`

## API

```http
POST /analysis/change-detection
GET /analysis/{id}/changes
POST /analysis/{id}/exports/change-geojson
```

## UI requirements

Change Lab must support:

- dataset/layer A selector
- dataset/layer B selector
- method selector
- area selector
- threshold controls
- timeline labels
- map overlays for added/removed/modified
- metrics cards
- export

## V1 target

Implement vector change detection. Raster and AI-based change detection are later phases.