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Geometry

get_polygon_center

supervision.geometry.utils.get_polygon_center(polygon: npt.NDArray[np.float64]) -> Point

Calculate the center of a polygon. The center is calculated as the center of the solid figure formed by the points of the polygon

Parameters:

Name Type Description Default

polygon

NDArray[float64]

A 2-dimensional numpy ndarray representing the vertices of the polygon.

 required

Returns:

Type Description
Point

The center of the polygon, represented as a Point object with x and y attributes.

Raises:

Type Description
ValueError

If the polygon has no vertices.

Examples:

>>> import numpy as np
>>> import supervision as sv
>>> polygon = np.array([[0, 0], [0, 2], [2, 2], [2, 0]])
>>> center = sv.get_polygon_center(polygon=polygon)
>>> float(center.x)
1.0
>>> float(center.y)
1.0
Source code in src/supervision/geometry/utils.py 
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def get_polygon_center(polygon: npt.NDArray[np.float64]) -> Point:
    """
    Calculate the center of a polygon. The center is calculated as the center
    of the solid figure formed by the points of the polygon

    Args:
        polygon: A 2-dimensional numpy ndarray representing the vertices of the
            polygon.

    Returns:
        The center of the polygon, represented as a Point object with x and y
            attributes.

    Raises:
        ValueError: If the polygon has no vertices.

    Examples:
        ```pycon
        >>> import numpy as np
        >>> import supervision as sv
        >>> polygon = np.array([[0, 0], [0, 2], [2, 2], [2, 0]])
        >>> center = sv.get_polygon_center(polygon=polygon)
        >>> float(center.x)
        1.0
        >>> float(center.y)
        1.0

        ```
    """

    # This is one of the 3 candidate algorithms considered for centroid calculation.
    # For a more detailed discussion, see PR #1084 and commit eb33176

    if len(polygon) == 0:
        raise ValueError("Polygon must have at least one vertex.")

    shift_polygon = np.roll(polygon, -1, axis=0)
    signed_areas = np.cross(polygon, shift_polygon) / 2
    if signed_areas.sum() == 0:
        center = np.mean(polygon, axis=0).round()
        return Point(x=center[0], y=center[1])
    centroids = (polygon + shift_polygon) / 3.0
    center = np.average(centroids, axis=0, weights=signed_areas).round()

    return Point(x=center[0], y=center[1])

Position

supervision.geometry.core.Position

Bases: Enum

Enum representing the position of an anchor point.

Source code in src/supervision/geometry/core.py 
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class Position(Enum):
    """
    Enum representing the position of an anchor point.
    """

    CENTER = "CENTER"
    CENTER_LEFT = "CENTER_LEFT"
    CENTER_RIGHT = "CENTER_RIGHT"
    TOP_CENTER = "TOP_CENTER"
    TOP_LEFT = "TOP_LEFT"
    TOP_RIGHT = "TOP_RIGHT"
    BOTTOM_LEFT = "BOTTOM_LEFT"
    BOTTOM_CENTER = "BOTTOM_CENTER"
    BOTTOM_RIGHT = "BOTTOM_RIGHT"
    CENTER_OF_MASS = "CENTER_OF_MASS"

    @classmethod
    def list(cls) -> list[str]:
        return list(map(lambda c: c.value, cls))

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