API documentation

Fix antimeridian crossings in GeoJSON objects and shapely geometries.

FixWindingWarning

Bases: AntimeridianWarning

The input shape is wound clockwise (instead of counter-clockwise), so this package is reversing the winding order before fixing the shape.

Source code in src/antimeridian/_implementation.py

class FixWindingWarning(AntimeridianWarning):
    """The input shape is wound clockwise (instead of counter-clockwise), so
    this package is reversing the winding order before fixing the shape.
    """

    MESSAGE = (
        "The exterior ring of this shape is wound "
        "clockwise. Since this is a common error in real-world "
        "geometries, this package is reversing the exterior coordinates of the "
        "input shape before running its algorithm. If you know that your input "
        "shape is correct (i.e. if your data encompasses both poles), pass "
        "`fix_winding=False`."
    )

    @classmethod
    def warn(cls) -> None:
        warnings.warn(cls.MESSAGE, cls, stacklevel=2)

GeoInterface

Bases: Protocol

A simple protocol for things that have a __geo_interface__ method.

The __geo_interface__ protocol is described here, and is used within shapely to extract geometries from objects.

Source code in src/antimeridian/_implementation.py

class GeoInterface(Protocol):
    """A simple protocol for things that have a `__geo_interface__` method.

    The `__geo_interface__` protocol is described
    [here](https://gist.github.com/sgillies/2217756>), and is used within
    [shapely](https://shapely.readthedocs.io/en/stable/manual.html) to extract
    geometries from objects.
    """

    @property
    def __geo_interface__(self) -> Dict[str, Any]: ...

bbox

bbox(shape: Dict[str, Any] | GeoInterface, force_over_antimeridian: bool = False) -> List[float]

Calculates a GeoJSON-spec conforming bounding box for a shape.

Per the GeoJSON spec, an antimeridian-spanning bounding box should have its larger longitude as its first bounding box coordinate.

Parameters:

• shape (Dict[str, Any] | GeoInterface) –

  The polygon or multipolygon for which to calculate the bounding box.

• force_over_antimeridian (bool, default: False ) –

  Force the bounding box to be over the antimeridian.

Returns:

• List[float] –

  List[float]: The bounding box.

Source code in src/antimeridian/_implementation.py

def bbox(
    shape: Dict[str, Any] | GeoInterface, force_over_antimeridian: bool = False
) -> List[float]:
    """Calculates a GeoJSON-spec conforming bounding box for a shape.

    Per the [GeoJSON
    spec](https://datatracker.ietf.org/doc/html/rfc7946#section-5.2), an
    antimeridian-spanning bounding box should have its larger longitude as its
    first bounding box coordinate.

    Args:
        shape: The polygon or multipolygon for which to calculate the bounding box.
        force_over_antimeridian: Force the bounding box to be over the antimeridian.

    Returns:
        List[float]: The bounding box.
    """
    geom = shapely.geometry.shape(shape)
    if geom.geom_type == "Polygon":
        return list(geom.bounds)
    elif geom.geom_type == "MultiPolygon":
        crosses_antimeridian = False
        xmins = list()
        ymin = 90
        xmaxs = list()
        ymax = -90
        for polygon in geom.geoms:
            bounds = polygon.bounds
            xmins.append(bounds[0])
            if bounds[1] < ymin:
                ymin = bounds[1]
            xmaxs.append(bounds[2])
            if bounds[3] > ymax:
                ymax = bounds[3]
            if is_coincident_to_antimeridian(polygon) and not (
                bounds[0] == -180 and bounds[2] == 180
            ):
                crosses_antimeridian = True

        if crosses_antimeridian or force_over_antimeridian:
            return [max(xmins), ymin, min(xmaxs), ymax]
        else:
            return [min(xmins), ymin, max(xmaxs), ymax]
    else:
        raise ValueError(
            f"unsupported geom_type for bbox calculation: {geom.geom_type}"
        )

centroid

centroid(shape: Dict[str, Any] | GeoInterface) -> Point

Calculates the centroid for a polygon or multipolygon.

Polygons are easy, we just use shapely.centroid. For multi-polygons, the antimeridian is taken into account by calculating the centroid from an identical multi-polygon with coordinates in [0, 360).

Parameters:

• shape (Dict[str, Any] | GeoInterface) –

  The polygon or multipolygon for which to calculate the centroid.

Returns:

• Point ( Point ) –

  The centroid.

Source code in src/antimeridian/_implementation.py

def centroid(shape: Dict[str, Any] | GeoInterface) -> Point:
    """Calculates the centroid for a polygon or multipolygon.

    Polygons are easy, we just use [shapely.centroid][]. For
    multi-polygons, the antimeridian is taken into account by calculating the
    centroid from an identical multi-polygon with coordinates in [0, 360).

    Args:
        shape: The polygon or multipolygon for which to calculate the centroid.

    Returns:
        Point: The centroid.
    """
    # Inspired by
    # https://github.com/stactools-packages/sentinel2/blob/f90f5fa006459e9bb59bfd327d9199e5259ec4a7/src/stactools/sentinel2/stac.py#L192-L208
    geom = shapely.geometry.shape(shape)
    if geom.geom_type == "Polygon":
        return cast(Point, geom.centroid)
    elif geom.geom_type == "MultiPolygon":
        geoms = list()
        for component in geom.geoms:
            if any(c[0] < 0 for c in component.exterior.coords):
                geoms.append(shapely.affinity.translate(component, xoff=+360))
            else:
                geoms.append(component)
        centroid = cast(
            Point, shapely.validation.make_valid(MultiPolygon(geoms)).centroid
        )
        if centroid.x > 180:
            centroid = Point(centroid.x - 360, centroid.y)
        return centroid
    else:
        raise ValueError(
            f"unsupported geom_type for centroid calculation: {geom.geom_type}"
        )

fix_geojson

fix_geojson(geojson: Dict[str, Any], *, force_north_pole: bool = False, force_south_pole: bool = False, fix_winding: bool = True) -> Dict[str, Any]

Fixes a GeoJSON object that crosses the antimeridian.

If the object does not cross the antimeridian, it is returned unchanged.

See antimeridian.fix_polygon for a description of the force_north_pole force_south_pole and fix_winding arguments.

Parameters:

• geojson (Dict[str, Any]) –

  A GeoJSON object as a dictionary

• force_north_pole (bool, default: False ) –

  If the polygon crosses the antimeridian, force the joined segments to enclose the north pole.

• force_south_pole (bool, default: False ) –

  If the polygon crosses the antimeridian, force the joined segments to enclose the south pole.

• fix_winding (bool, default: True ) –

  If the polygon is wound clockwise, reverse its coordinates before applying the algorithm.

Return

The same GeoJSON with a fixed geometry or geometries

Source code in src/antimeridian/_implementation.py

def fix_geojson(
    geojson: Dict[str, Any],
    *,
    force_north_pole: bool = False,
    force_south_pole: bool = False,
    fix_winding: bool = True,
) -> Dict[str, Any]:
    """Fixes a GeoJSON object that crosses the antimeridian.

    If the object does not cross the antimeridian, it is returned unchanged.

    See [antimeridian.fix_polygon][] for a description of the `force_north_pole`
    `force_south_pole` and `fix_winding` arguments.

    Args:
        geojson: A GeoJSON object as a dictionary
        force_north_pole: If the polygon crosses the antimeridian, force the
            joined segments to enclose the north pole.
        force_south_pole: If the polygon crosses the antimeridian, force the
            joined segments to enclose the south pole.
        fix_winding: If the polygon is wound clockwise, reverse its
            coordinates before applying the algorithm.

    Return:
        The same GeoJSON with a fixed geometry or geometries
    """
    type_ = geojson.get("type", None)
    if type_ is None:
        raise ValueError("no 'type' field found in GeoJSON")
    elif type_ == "Feature":
        geometry = geojson.get("geometry", None)
        if geometry is None:
            raise ValueError("no 'geometry' field found in GeoJSON Feature")
        geojson["geometry"] = fix_shape(
            geometry,
            force_north_pole=force_north_pole,
            force_south_pole=force_south_pole,
            fix_winding=fix_winding,
        )
        return geojson
    elif type_ == "FeatureCollection":
        features = geojson.get("features", None)
        if features is None:
            raise ValueError("no 'features' field found in GeoJSON FeatureCollection")
        for i, feature in enumerate(features):
            features[i] = fix_geojson(
                feature,
                force_north_pole=force_north_pole,
                force_south_pole=force_south_pole,
                fix_winding=fix_winding,
            )
        geojson["features"] = features
        return geojson
    else:
        return fix_shape(
            geojson,
            force_north_pole=force_north_pole,
            force_south_pole=force_south_pole,
            fix_winding=fix_winding,
        )

fix_line_string

fix_line_string(line_string: LineString) -> Union[LineString, MultiLineString]

Fixes a shapely.LineString.

Parameters:

• line_string (LineString) –

  The input line string

Returns:

• Union[LineString, MultiLineString] –

  The fixed line string, either as a single line string or a multi-line

• Union[LineString, MultiLineString] –

  string (if it was split)

Source code in src/antimeridian/_implementation.py

def fix_line_string(line_string: LineString) -> Union[LineString, MultiLineString]:
    """Fixes a [shapely.LineString][].

    Args:
        line_string: The input line string

    Returns:
        The fixed line string, either as a single line string or a multi-line
        string (if it was split)
    """
    segments = segment(list(line_string.coords))
    if not segments:
        return line_string
    else:
        return MultiLineString(segments)

fix_multi_line_string

fix_multi_line_string(multi_line_string: MultiLineString) -> MultiLineString

Fixes a shapely.MultiLineString.

Parameters:

• multi_line_string (MultiLineString) –

  The input multi line string

Returns:

• MultiLineString –

  The fixed multi line string

Source code in src/antimeridian/_implementation.py

def fix_multi_line_string(multi_line_string: MultiLineString) -> MultiLineString:
    """Fixes a [shapely.MultiLineString][].

    Args:
        multi_line_string: The input multi line string

    Returns:
        The fixed multi line string
    """
    line_strings = list()
    for line_string in multi_line_string.geoms:
        fixed = fix_line_string(line_string)
        if isinstance(fixed, LineString):
            line_strings.append(fixed)
        else:
            line_strings.extend(fixed.geoms)
    return MultiLineString(line_strings)

fix_multi_polygon

fix_multi_polygon(multi_polygon: MultiPolygon, *, force_north_pole: bool = False, force_south_pole: bool = False, fix_winding: bool = True) -> MultiPolygon

Fixes a shapely.MultiPolygon.

See antimeridian.fix_polygon for a description of the force_north_pole force_south_pole and fix_winding arguments.

Parameters:

• multi_polygon (MultiPolygon) –

  The multi-polygon

• force_north_pole (bool, default: False ) –

  If the polygon crosses the antimeridian, force the joined segments to enclose the north pole.

• force_south_pole (bool, default: False ) –

  If the polygon crosses the antimeridian, force the joined segments to enclose the south pole.

• fix_winding (bool, default: True ) –

  If the polygon is wound clockwise, reverse its coordinates before applying the algorithm.

Returns:

• MultiPolygon –

  The fixed multi-polygon

Source code in src/antimeridian/_implementation.py

def fix_multi_polygon(
    multi_polygon: MultiPolygon,
    *,
    force_north_pole: bool = False,
    force_south_pole: bool = False,
    fix_winding: bool = True,
) -> MultiPolygon:
    """Fixes a [shapely.MultiPolygon][].

    See [antimeridian.fix_polygon][] for a description of the `force_north_pole`
    `force_south_pole` and `fix_winding` arguments.

    Args:
        multi_polygon: The multi-polygon
        force_north_pole: If the polygon crosses the antimeridian, force the
            joined segments to enclose the north pole.
        force_south_pole: If the polygon crosses the antimeridian, force the
            joined segments to enclose the south pole.
        fix_winding: If the polygon is wound clockwise, reverse its
            coordinates before applying the algorithm.

    Returns:
        The fixed multi-polygon
    """
    polygons = list()
    for polygon in multi_polygon.geoms:
        polygons += fix_polygon_to_list(
            polygon,
            force_north_pole=force_north_pole,
            force_south_pole=force_south_pole,
            fix_winding=fix_winding,
        )
    return MultiPolygon(polygons)

fix_polygon

fix_polygon(polygon: Polygon, *, force_north_pole: bool = False, force_south_pole: bool = False, fix_winding: bool = True) -> Union[Polygon, MultiPolygon]

Fixes a shapely.Polygon.

If the input polygon is wound clockwise, it will be fixed to be wound counterclockwise unless fix_winding is False in which case it will be corrected by adding a counterclockwise polygon from (-180, -90) to (180, 90) as its exterior.

In rare cases, the underlying algorithm might need a little help to fix the polygon. For example, a polygon that just barely crosses over a pole might have very few points at high latitudes, leading to ambiguous antimeridian crossing points and invalid geometries. We provide two flags, force_north_pole and force_south_pole for those cases. Most users can ignore these flags.

If either force_north_pole or force_south_pole is True fix_winding is set to False

Parameters:

• polygon (Polygon) –

  The input polygon

• force_north_pole (bool, default: False ) –

  If the polygon crosses the antimeridian, force the joined segments to enclose the north pole.

• force_south_pole (bool, default: False ) –

  If the polygon crosses the antimeridian, force the joined segments to enclose the south pole.

• fix_winding (bool, default: True ) –

  If the polygon is wound clockwise, reverse its coordinates before applying the algorithm.

Returns:

• Union[Polygon, MultiPolygon] –

  The fixed polygon, either as a single polygon or a multi-polygon (if it

• Union[Polygon, MultiPolygon] –

  was split)

Source code in src/antimeridian/_implementation.py

def fix_polygon(
    polygon: Polygon,
    *,
    force_north_pole: bool = False,
    force_south_pole: bool = False,
    fix_winding: bool = True,
) -> Union[Polygon, MultiPolygon]:
    """Fixes a [shapely.Polygon][].

    If the input polygon is wound clockwise, it will be fixed to be wound
    counterclockwise _unless_ `fix_winding` is `False` in which case it
    will be corrected by adding a counterclockwise polygon from (-180, -90) to
    (180, 90) as its exterior.

    In rare cases, the underlying algorithm might need a little help to fix the polygon.
    For example, a polygon that just barely crosses over a pole might have very
    few points at high latitudes, leading to ambiguous antimeridian crossing
    points and invalid geometries. We provide two flags, `force_north_pole`
    and `force_south_pole` for those cases. Most users can ignore these
    flags.

    If either `force_north_pole` or `force_south_pole` is `True`
    `fix_winding` is set to `False`

    Args:
        polygon: The input polygon
        force_north_pole: If the polygon crosses the antimeridian, force the
            joined segments to enclose the north pole.
        force_south_pole: If the polygon crosses the antimeridian, force the
            joined segments to enclose the south pole.
        fix_winding: If the polygon is wound clockwise, reverse its
            coordinates before applying the algorithm.

    Returns:
        The fixed polygon, either as a single polygon or a multi-polygon (if it
        was split)
    """
    if force_north_pole or force_south_pole:
        fix_winding = False
    polygons = fix_polygon_to_list(
        polygon,
        force_north_pole=force_north_pole,
        force_south_pole=force_south_pole,
        fix_winding=fix_winding,
    )
    if len(polygons) == 1:
        polygon = polygons[0]
        if shapely.is_ccw(polygon.exterior):
            return polygon
        else:
            return Polygon(
                [(-180, 90), (-180, -90), (180, -90), (180, 90)],
                [polygon.exterior.coords],
            )
    else:
        return MultiPolygon(polygons)

fix_shape

fix_shape(shape: Dict[str, Any] | GeoInterface, *, force_north_pole: bool = False, force_south_pole: bool = False, fix_winding: bool = True) -> Dict[str, Any]

Fixes a shape that crosses the antimeridian.

See antimeridian.fix_polygon for a description of the force_north_pole force_south_pole and fix_winding arguments.

Parameters:

• shape (Dict[str, Any] | GeoInterface) –

  A polygon, multi-polygon, line string, or multi-line string, either as a dictionary or as a antimeridian.GeoInterface. Uses shapely.geometry.shape under the hood.

• force_north_pole (bool, default: False ) –

  If the polygon crosses the antimeridian, force the joined segments to enclose the north pole.

• force_south_pole (bool, default: False ) –

  If the polygon crosses the antimeridian, force the joined segments to enclose the south pole.

• fix_winding (bool, default: True ) –

  If the polygon is wound clockwise, reverse its coordinates before applying the algorithm.

Returns:

• Dict[str, Any] –

  The fixed shape as a dictionary

Source code in src/antimeridian/_implementation.py

def fix_shape(
    shape: Dict[str, Any] | GeoInterface,
    *,
    force_north_pole: bool = False,
    force_south_pole: bool = False,
    fix_winding: bool = True,
) -> Dict[str, Any]:
    """Fixes a shape that crosses the antimeridian.

    See [antimeridian.fix_polygon][] for a description of the `force_north_pole`
    `force_south_pole` and `fix_winding` arguments.

    Args:
        shape: A polygon, multi-polygon, line string, or multi-line string,
            either as a dictionary or as a [antimeridian.GeoInterface][]. Uses
            [shapely.geometry.shape][] under the hood.
        force_north_pole: If the polygon crosses the antimeridian, force the
            joined segments to enclose the north pole.
        force_south_pole: If the polygon crosses the antimeridian, force the
            joined segments to enclose the south pole.
        fix_winding: If the polygon is wound clockwise, reverse its
            coordinates before applying the algorithm.

    Returns:
        The fixed shape as a dictionary
    """
    geom = shapely.geometry.shape(shape)
    if geom.geom_type == "Polygon":
        return cast(
            Dict[str, Any],
            shapely.geometry.mapping(
                fix_polygon(
                    geom,
                    force_north_pole=force_north_pole,
                    force_south_pole=force_south_pole,
                    fix_winding=fix_winding,
                )
            ),
        )
    elif geom.geom_type == "MultiPolygon":
        return cast(
            Dict[str, Any],
            shapely.geometry.mapping(
                fix_multi_polygon(
                    geom,
                    force_north_pole=force_north_pole,
                    force_south_pole=force_south_pole,
                    fix_winding=fix_winding,
                )
            ),
        )
    elif geom.geom_type == "LineString":
        return cast(Dict[str, Any], shapely.geometry.mapping(fix_line_string(geom)))
    elif geom.geom_type == "MultiLineString":
        return cast(
            Dict[str, Any], shapely.geometry.mapping(fix_multi_line_string(geom))
        )
    else:
        raise ValueError(f"unsupported geom_type: {geom.geom_type}")

segment_geojson

segment_geojson(geojson: Dict[str, Any]) -> MultiLineString

Segments a GeoJSON object into a MultiLineString.

If the object does not cross the antimeridian, its exterior and interior line strings are returned unchanged.

Parameters:

• geojson (Dict[str, Any]) –

  A GeoJSON object as a dictionary

Return

A MutliLineString of segments.

Source code in src/antimeridian/_implementation.py

def segment_geojson(geojson: Dict[str, Any]) -> MultiLineString:
    """Segments a GeoJSON object into a MultiLineString.

    If the object does not cross the antimeridian, its exterior and interior
    line strings are returned unchanged.

    Args:
        geojson: A GeoJSON object as a dictionary

    Return:
        A MutliLineString of segments.
    """
    type_ = geojson.get("type", None)
    if type_ is None:
        raise ValueError("no 'type' field found in GeoJSON")
    elif type_ == "Feature":
        geometry = geojson.get("geometry", None)
        if geometry is None:
            raise ValueError("no 'geometry' field found in GeoJSON Feature")
        return MultiLineString(segment_shape(geometry))
    elif type_ == "FeatureCollection":
        features = geojson.get("features", None)
        if features is None:
            raise ValueError("no 'features' field found in GeoJSON FeatureCollection")
        segments = list()
        for feature in features:
            segments.extend(segment_geojson(feature))
        return MultiLineString(segments)
    else:
        return MultiLineString(segment_shape(geojson))