> For the complete documentation index, see [llms.txt](https://cityweft.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cityweft.gitbook.io/docs/basics/coordinate-systems-crs.md).

# Coordinate Systems (CRS)

| CRS                                                                                                                | Description                   | Use Case                                 | Coordinates          |
| ------------------------------------------------------------------------------------------------------------------ | ----------------------------- | ---------------------------------------- | -------------------- |
| <p>local<br><br><a data-mention href="#local-coordinate-system">#local-coordinate-system</a></p>                   | Relative to origin point      | Small sites, game engines, visualization | Meters from origin   |
| <p>EPSG:3857<br><br><a data-mention href="#web-mercator-epsg-3857">#web-mercator-epsg-3857</a></p>                 | Web Mercator                  | Web mapping, global applications         | Global Web Mercator  |
| <p>UTM<br><br><a data-mention href="#universal-transverse-mercator-utm">#universal-transverse-mercator-utm</a></p> | Universal Transverse Mercator | GIS, surveying, precise mapping          | UTM zone coordinates |

## Local Coordinate System

Parameter: `crs: "local"`  (default)

#### Description

The local coordinate system positions all geometry relative to a specified origin point. This creates a localized coordinate space with the origin at (0,0,0).

#### Characteristics

* Origin: User-defined point or first polygon vertex
* Units: Meters
* Coordinate Space: X-right, Y-forward/back, Z-up (depending on upAxis parameter)
* Range: Suitable for sites up to \~10km radius

#### When to Use

* ✅ Game engines (Unity, Unreal)
* ✅ 3D visualization applications
* ✅ Small to medium-sized sites
* ✅ When you need simple, relative coordinates
* ❌ Large geographical areas (>10km)
* ❌ When integrating with GIS systems

#### Output format:

```json
{
  "spatialReference": {
    "crs": "local",
    "origin": [52.5200, 13.4050]
  },
  "geometry": [...] // Coordinates relative to origin
}
```

### Web Mercator (EPSG:3857)

Parameter: `crs: "EPSG:3857"`&#x20;

#### Description

Web Mercator is the standard projection used by most web mapping services (Google Maps, OpenStreetMap, Mapbox). Coordinates are in the global Web Mercator coordinate system.

#### Characteristics

* Origin: Global (0,0) at the intersection of the equator and the prime meridian
* Units: Meters (keep in mind the Mercator distortion)
* Projection: Spherical Mercator

#### When to Use

* ✅ Web mapping applications
* ✅ Integration with web map services
* ✅ Global or continental-scale projects
* ✅ When working with existing Web Mercator data
* ❌ High-precision surveying
* ❌ Polar regions (>85° latitude)

#### Output format:

```json
{
  "spatialReference": {
    "crs": "EPSG:3857"
  },
  "geometry": [...] // Global Web Mercator coordinates
}
```

### Universal Transverse Mercator (UTM)

Parameter:  `crs:"UTM"`&#x20;

#### Description

UTM divides the world into 60 zones, each 6° wide (with some exceptions like Norway mainland and Svalbard). The system automatically detects the appropriate UTM zone based on your polygon's location and provides high-precision coordinates.

#### Characteristics

* Origin: Zone-specific (500,000m Easting, 0m or 10,000,000m Northing)
* Units: Meters
* Projection: Transverse Mercator per zone
* Accuracy: Sub-meter precision within zone
* Auto-detection: Zone calculated from the polygon center

#### When to Use

* ✅ GIS applications (QGIS, ArcGIS)
* ✅ Surveying and engineering
* ✅ High-precision mapping
* ✅ CAD integration
* ✅ Construction and infrastructure projects
* ❌ Cross-zone projects (spanning >6° longitude)
* ❌ Simple visualization needs

\
**Output format**

```json
{
  "spatialReference": {
    "crs": "UTM",
    "utmZoneEPSG": "EPSG:32633",
    "zoneString": "33N",
    "hemisphere": "N",
    "zone": 33,
    "letter": "N"
  },
  "geometry": [...] // UTM zone coordinates
}
```

## Integration Compatibility

| Software Type | Recommended CRS |
| ------------- | --------------- |
| Game Engines  | local           |
| Web Maps      | EPSG:3857       |
| GIS Software  | UTM             |
| CAD Software  | UTM or local    |
| 3D Modeling   | local           |

#### Error Handling

* Invalid CRS values default to 'local'
* UTM zones are auto-calculated; manual specification is not required
* Cross-zone polygons use the zone of the polygon centroid

#### Performance Notes

* Local & EPSG:3857: Fastest processing, minimal coordinate transformations
* UTM: Slightly slower, requires zone calculation and transformation


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