Antimeridian

0.4.7 verified Mon Apr 27 auth: no python

Corrects GeoJSON geometries (Polygons, MultiPolygons, etc.) that cross the 180th meridian (antimeridian). Splits them into valid, non-wrapping geometries. Current version: 0.4.7. Release cadence: infrequent, as needed.

pip install antimeridian

Common errors

error ValueError: Expected a GeoJSON geometry object, got list ↓

cause Passed a list of coordinates instead of a geometry dict.

fix

Wrap coordinates in a valid GeoJSON structure: {'type': 'Polygon', 'coordinates': your_list}

error antimeridian.InvalidGeometryError: Geometry type not supported: LineString ↓

cause Attempted to fix a non-polygonal geometry type that antimeridian cannot handle.

fix

Only Polygon, MultiPolygon, and their derivatives (e.g., in a Feature) are supported. For other types, use other libraries or preprocess.

error TypeError: fix_geojson() missing 1 required positional argument: 'geometry' ↓

cause Called fix_geojson without arguments or with incorrect keyword.

fix

Use: fix_geojson(geometry_dict)

Warnings

gotcha fix_geojson returns a new dictionary; it does not modify the input in place. Do not assume mutation. ↓

fix Always assign the result: fixed = fix_geojson(original)

gotcha The function may raise InvalidGeometryError if the input is not a valid GeoJSON geometry object (e.g., missing 'type' or 'coordinates'). ↓

fix Validate your GeoJSON structure before passing it. Wrap in try/except if needed.

breaking Version 0.4.0 changed the internal splitting algorithm, which may produce different output shapes for edge cases (e.g., geometries that touch the antimeridian). ↓

fix Test your specific geometries after upgrading. Old behavior can't be restored.

Imports

fix_geojson
wrong
```
import antimeridian
```
correct
```
from antimeridian import fix_geojson
```
Top-level function; no more antimeridian.fix_geojson() needed; direct import recommended.
fix_polygon
```
from antimeridian import fix_polygon
```
Lower-level function for single polygons.

Quickstart

Correct a simple polygon crossing the antimeridian (180° longitude).

from antimeridian import fix_geojson
import json

geojson = {
    "type": "Polygon",
    "coordinates": [[
        [179.0, -10.0],
        [-179.0, -10.0],
        [-179.0, 10.0],
        [179.0, 10.0],
        [179.0, -10.0]
    ]]
}

# Fix the geometry
fixed = fix_geojson(geojson)
print(json.dumps(fixed, indent=2))